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• POST a QUESTION or READ FAQs about Aquastats controls used on Heating Boilers

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Heating aquastat repair:

Guide to diagnostic troubleshooting for heating boiler aquastat controls: this article describes common operating problems with heating system aquastat controls and how these troubles are diagnosed and fixed.

We discuss aquastat problems such as improper adjustment, improper wiring, and relay buzzing or failures.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Aquastat Boiler Control Diagnostic Troubleshooting Guide

Shown above, a hydronic heating system circulator pump relay control with its cover removed. The basic components and connections in the circulator relay include:

• Green arrow: Line voltage in - 120VAC power to operate the circultor pump (white and black wires) usually labeled L1 and L2
• Blue arrow: thermostat wires - low voltage circuit from thermostat that operates the circulator relay usually labelled T and T1
• Yellow arrow: 24VAC transformer that operates switches and controls within the relay control assembly
• Red arrow: the circulator relay switch
• Circulator control terminals C1 and C2 are at the lower right side of the circuit board in our photo
• Burner control terminals B1 and B2 are at the upper right on the circuit board in our photo

[Click to enlarge any image]

How to Diagnose & Fix an Aquastat Control on a Heating Boiler

If you have not already done so, we suggest reviewing the basic operation of a heating boiler aquastat described

at AQUASTAT CONTROLS

Then see AQUASTAT HI LO DIFF SETTINGS to be sure your control has been set properly.

[Click to enlarge any image]

Question: what basic tests can I do to diagnos a clicking aquastat relay or other issues?

Just install a new aquastat to my gas boier it continues to click. so turn it off. - Wayne, 2017/11/29

This Q&A were posted originally at AQUASTAT CONTROLS - home

Reply: try these basic Aquastat troubleshooting steps to check for power

Wayne,

Check first for a loose wire or bad electrical connection.

If clicking continues let's look more closely at what is clicking - probably a relay switch in the aquastat.

If so, check the connections to the circulator or burner that the aquastat is trying to operate. If those were working before, and apologizing that I am shooting from the hip, let's do these basic aquastat tests. If none of those sort this out I'm left suspecting a bad relay and thus a bad control.

Tell me the control brand and model and I'll check further.

How to Conduct Basic Boiler Aquastat Controller Tests:

1. Turn thermostat down -
Turn the wall thermostat all the way down so it is not calling for heat.

2. Check incoming voltage -
Using a DMM or VOM check for line voltage (120VAC) at the power terminals to the aquastat (i.e. power is on) by finding 120VAc at the two Line-IN terminals, L1 and L3 are typical markings.

Watch out: opening the cover and / or touching electrical connections while power is on to any electrical device risks shock or death by electrocution. If you know do not know how to do this safely STOP and ask for help from a trained service technician or licensed electrician.

3. Check the low voltage transformer output:
Check for 24VAC at the T and TV terminals - you will find 24VAC at one of these and 0 VAC at the other.
If both terminals show 0 volts then the transformer is bad.

4. Check thermostat switch terminals:
Now turn the Thermostat all the way UP so that it is calling for heat (remember to set it back down later). You should see 24VAC on BOTH of the thermostat or TT terminals inside the aquastat. If you don't then the thermostat is not calling for heat and most-likely you've got an open thermostat wire or a bad thermostat itself.

5. Check burner power terminals:
Now while still calling for heat, check that the aquastat is sending 120VAC voltage to the burner (the two B terminals B1 and B2) confirming that the aquastat is trying to turn on the burner (oil burner) or trying to open the gas valve if it's a gas boiler. This should be turning on the burner.

6. Check circulator terminals:
Now while still calling for heat, check that the aquastat is also sending voltage to the circulator pump - look for 120VAC at the C1 and C2 terminals. This should be turning on the circulator.

If voltage is everywhere it should be and a relay is clicking constantly OR a transformer is buzzing, those component(s) are probably bad.

Separately at RELAY CONTROL SWITCHES using a water pump pressure control switch as an example we discuss clicking and chattering relay switches.

While it is possible to replace a bad relay switch on an aquastat few technicians do so. More often the tech replaces the entire control.

Also see CIRCULATOR PUMP RELAYS & OTHER CONTROLS.

Question: are there re-built primary controls for boilers?

i had an issue with my boiler , i figured it out it was my aquastats l8124,any I called my local place and was told a used one was 190.00 rebuilt?? i was told by another place there are no rebuilt aquastats.help!!!!!!
ptsd1969@hotmail.com - Anon 10/3/12

Reply:

Some heating equipment suppliers can provide re-built as well as new primary controls. The folks who told you there are no rebuilt aquastats - well I'm not sure if that's because they didn't know or they didn't sell.

Question: Buzzing sounds from heating controls

When my oil burner is starting up I hear a loud buzzing from the boiler room.

Reply: check for a bad relay or a relay that is being impeded by the control cover

Buzzing noisy aquastats, also any other heating controls that use relays, such as some cad cells, stack relays, and circulator relays: if you hear a buzzing sound coming from your aquastat check to see if the control cover is pressing down on one of its relays. Details, photographs, and an explanation are

at HEATING SYSTEM NOISE DIAGNOSIS.

Also check for a bad relay in the control. Often a failing relay unit will buzz in a heating system control.

Question: Boiler won't run: when one of my three thermostats calls for heat the circulator runs but the boiler does not

I have a three zone hot water baseboard heating system. I have three zone valves and only one circulator pump.

My zone valves are made by honeywell and I believe they are the newer version. When I raise the thermostat (upstairs zone) I can hear the circulator pump kick on, the switch on top of the zone valve is in open position and I can hear a click come from the boiler.

The problem is that the boiler never comes on to heat the water to a sufficient temperature. When I put my hand on the pipe directly coming out of this zone valve the it is warm at best. My baseboards upstairs never really get that hot and are unable to raise the temperature in the upstairs of the house.

When I operate the other thermostats in the other zones of the house, the furnace kicks on and heats the the water to temperature. What could be causing the furnace to not kick on in the in the one zone? - Joe.

Reply: from reader Joe P.

If it is only in the one zone you describe: it may be that the boiler is up to temperature and does not need to 'kick on'.

Observe the temperature on the gauge. Small loops/zones do not take the heat away as fast. Also, there could be blockage. I have also seen in homes that set the thermostats to low, that freezing occurs in the loop, and thus, poor heat output.

You also may have air in the lines which will have to be purged. Turn down t-stat to lower temperature so that all heating goes to the troubled loop and see what happens.

Clarification: Turn down the t-stats to the two other loops (that are working) so that all heat goes to the troubled loop that you have activated (via t-stat for troubled loop).

Reply-DF:

Joe, from your description we can exclude the case that the boiler does not run because it's already up to temperature - since you say that you feel no heat in the problem circulator piping and baseboards.

We like Joe P's advice to see what happens when you turn down or up thermostats to the other zones. Here are more diagnostics:

Heating zone air bound or stuck zone valve: Joe P. refers to a possible blockage in the problem heating zone. Indeed if the zone is air-bound.
See AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE

Or if the zone valve motor is itself stuck then even though the system circulator runs, it never pushes hot boiler water out into the problem heating zone and therefore it never pushes cold water back from the problem heating zone into the boiler where that cooler water would cause the boiler to turn on.
See ZONE VALVES, HEATING

Question: Boiler sometimes won't run': some of my zone thermostats call for heat, the circulator runs, but the boiler won't come

When one or sometimes two of my three heating zone thermostats call for heat, the circulator runs, but for two of the zones, the boiler won't come on until the third zone thermostat is also calling for heat. - DF

Reply: check for a bad control, switch, or relay

This problem could be due to a wiring error or a control problem, as we detail below.

Burn-up on Honeywell Type L8182A, C L8151A Aquastat control board leaves one or two heating zones inoperative

[Click to enlarge any image]

We recently observed the symptoms, debugging, and solution to a similar no-heat in one zone problem. The zone was not air bound. Three thermostats control three individual zone circulators (Taco brand).

The thermostat for zone 3 in a house would call for heat, trip on the circulator, but the boiler would not turn on unless one of the other zones was calling for heat.

The second service tech (from Bottini Fuel, Poughkeepsie, the first fellow said he couldn't see anything wrong), traced the problem to a burned-out circuit on the aquastat control board. We replaced the aquastat and indeed now any thermostat that calls for heat can both turn on the circulator and if appropriate (based on temperatures at the boiler) turn on the boiler's oil or gas burner when it should.

Our photo of this very Honeywell L8124A aquastat control circuit board, with the wires removed, shows brown burn marks around the ZC terminal on the device.

(Photo above). Aside from more sophisticated circuit testing, you might spot this kind of trouble by simple visual inspection of electrical controls and components. Nothing should look 'burned-up'.

Watch out: a miswired multiple zone or multiple circulator pump system can also prevent one or more of the zones from operating correctly. So can a mix of different brands of zone valves that require different wiring.

Question: temperature difference between on and off too great

I have a 17 year old Rheem boiler which works just fine. However the temperature differential between on and off has become too great despite my setting the thermostat to 5 degrees. It is time for a new thermostat, but I don't know what to buy.

The cover on my thermostat says honeywell aquastat type l8100. eco thermostat. The body says L4005A2080. another part of the body says C0704. I have a blue and white wire to connect to the gas control. There is one bare copper wire going from the center of the thermostat screw on to the left side. That's all the description I have. - Alan 8/21/12

Reply:

Take a look at our room thermostat troubleshooting information

at THERMOSTATS, HEATING / COOLING

Mann worked on production for Master P's I'm Bout It, E-40's Southwest Riders, and Mr. Brotha lynch hung youtube.

- it would be a shame to replace equipment when all that was needed was to blow or vacuum dust off of the existing unit.

Question: Boiler will run but the circulator pump(s) do not ever start.

When any of my three heating zone thermostats call for heat, the boiler will run, but it seems to take forever for the baseboards to get warm, especially on the longer runs.

I finally figured that none of the circulators is running. Because there are three circulator pumps and circulator relays, each controlled by an individual wall thermostat, it seems unlikely that all of them are bad. What should I check? - Charlie G., Calais, Maine.

Reply: check the aquastat control settings for crossed or reversed HI LO controls, then check primary control relays

The photo (above left) illustrates Charlie's aquastat with improper settings for the HI and LO. The HI is set to 180 and the LO is set to just under 200!. Sorry Charlie G. but that's not going to work right.

We have found this problem lots of times when a homeowner or someone else messed around with the HI, LO, and DIFF settings on the aquastat without having a good idea of what those dials do. Aquastat manufacturers such as Honeywell make clear that

Hb Smith G200 Manual Transfer Case

The HI should always be set at least 20 °F. above the LO.

If you 'cross the controls' - that is, if you set the LO to a temperature that is less than 20 degrees lower than the HI setting, you have basically locked out the circulators.

The oil burner runs, but the LO control is preventing the circulator from coming on. Take a look at the definitions of HI and LO above and this will be more obvious.

Our photo immediately above shows settings that OK - the HI is set to a little over 180 and the LO is set to 160.

Question: my heating boiler won't start

this morning the boiler was not heating. It worked very well during the night. No light in the furnace. I turn off and turn on the gas ignition and nothing happened. What can be the problem? has the damper related to this issue?

I change the button from one side to another side and nothing.

Also, how can I switch on the spill gas? I think that the problem is the sensor, because it was smoke near the boiler area and maybe the sensor shut off the gas but I do not know where is it. My boiler is UTICA model. - Anon 11/7/12

Reply:

Anon, with just the information you state, I'd start at the beginning of our no-heat for boilers,

see DIAGNOSE & FIX HEATING PROBLEMS-BOILER - troubleshooting. Indeed there could be a bad flue gas spill sensor, but I wouldn't start there.

Question: Indirect fired water heater operation when a tankless coil is also available

I have a strange configuraton.

My DHW tank is a zone (tank was added after the fact), but only triggers the LO setting, so it doesn't get the the hotter water that my heating zones get. To complicate things, the water still passes through the tankless and the 'Temp-A-Rator' mixing valve.

So, in effect, I pre-heat my hot water. Bypassing the tankless would be expensive and I guess I'd need to then have the tank wired so that it triggers a higher water temp (additional aquastat?). I also don't understand this [apparently obsolete] mixing valve. Is it manual? Should I replace it?

Ok, I'm rambling. Would appreciate any and all thoughts. - Chris - Chris 5/10/12

Reply:

Chris,

When domestic hot water is made by a separate tank heated by a zone on the heating boiler, we call that an indirect-fired water heater system. The LO and DIFF settings have nothing to do with that water heating method - the LO and DIFF make sense and are used when there is a tankless coil in use.

The heating zone, control, and circulator pump (or zone valve) that heats your separate hot water tank just looks like another heating zone as far as the heating boiler and its controls are concerned. Hot water from inside the boiler itself circulates through a heating coil in the bottom of the hot water tank in response to a thermostat on the hot water tank.

But if a heating boiler uses a tankless coil as a pre-heater or post-heater for the water entering the hot water tank, then indeed you've got two water heating methods in parallel - which can be confusing. In fact, you can think of them separately, and controlled separately.

Take a look at the water piping that brings cold water from the building water supply into your hot water heating tank. If the cold water runs first through the tankless coil, then yes you are pre-heating water entering the hot water heater tank.

Some plumbers pipe in the opposite direction, that is, allowing hot water leaving the hot water tank to pass through the tankless coil for a boost that takes effect when the hot water in the separate tank is nearly used up or is cool.

See INDIRECT FIRED WATER HEATERS for details of how these systems work.

Question: L4081B aquastat doesn't seem to be behaving like it should

Great information here. I had to read a few times to put it all together, but I think I finally got it. I have an L4081B aquastat and it doesn't seem to be behaving like it should.
From a cold start with no call for heat (I turned down the thermostats) the burner stayed on all the way to the HI setting (in my case 180°). Shouldn't it cut off at the upper limit of the LO setting?
My Hi is set to 180° and LO at 130 with a 20° DIFF. I have a tankless coil. - Steve 11/7/2012

Reply:

If there is no call for heat but the boiler cycles on, I'd expect that ON cycle to be driven by the LO and DIFF controls just as you describe.

Question: my heater won't turn off; replacing the thermostat did no good, what do I try next?

my heater just don't stop heating my house i tried a new thermostat what should i try next please - Frank Carr 11/12/2012

Reply: things to check when the heat won't turn off, & some Safety Warnings

Buddy said: Frank, You may have a problem with your boiler controls or a check valve in the hot water piping system.

Take a look at 'Guide to Heating System Boiler Check Valves & Flow Control Valves' [to see if this information helps you determine if a check valve is sticking open.

In any case, you will probably need the services of a service technician to check out the controls or a plumber to replace a check valve if it is sticking open. - Buddy 11/12/2012
See CHECK VALVES, HEATING SYSTEM

Daniel (Moderator) said:

Frank: in addition to Buddy's suggestion just above, some other reasons that heat may not turn off in a building include:

• The thermostat is continuing to call for heat because it is in a draft, is damaged, or stuck
• The thermostat wires are shorted together anywhere in their run - this is the same as leaving the thermostat set to its highest setting.
• The aquastat or high limit temperature sensors are not properly sensing boiler water temperature because of a bad sensor or because the sensor was not properly mounted in its well on the boiler.
  The manufacturers recommend using a temperature-conducting grease, aka thermal grease, properly also called
  AQUASTAT SENSDOR PROBE HEAT CONDUCTING COMPOUND though some techs I know like to leave the grease off in hope of avoiding
  an AQUASTAT SENSOR PROBE STUCK in the AQUASTAT WELL
• The heating system is unable to adequately warm the room where the thermostat is located
• If the heating boiler keeps running but is unable to satisfy the thermostat,
  that is it can't get the room temperature up to the thermostat SET temperature there could be other problems such as
  • An air-bound heating pipe, baseboard or radiator that is just not delivering heat to the room where the thermostat is located.
    See AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE
  • The thermostat is on a cold exterior wall or is in a cold draft and is not properly sensing room temperature.
    See THERMOSTATS, HEATING / COOLING for details on thermostat installation, wiring, and setting.
• Watch out: some safety things to check when your heat won't turn off include
  • Check the heating boiler temperature gauge
    If the boiler temperature is at or above the HI limit set on your boiler aquastat or upper limit control switch then something is abnormal and unsafe and you should turn the system OFF immediately and call for heating system service and repair.
    See GAUGES ON HEATING EQUIPMENT
  • Check for discharge, drips, leaks, or spillage at the boiler's temperature/pressure relief valve.
    If if the boiler temperature is at or above the HI limit set on your boiler aquastat or upper limit control switch and the relief valve is not dumping hot water and pressure then something is abnormal and unsafe and you should turn the system OFF immediately and call for heating system service and repair.
    See RELIEF VALVES, BOILERS
    or for steam boilers see RELIEF VALVES, STEAM BOILERS
  In any case you should call a heating service technician to inspect and repair the system promptly.

Question: how do I find a replacement Aquastat for a Honeywell L8024B1048 (triple aquastat) ?

I have a Gas Hydrotherm 86000 Model R108 furnace. I cannot find a replacement Aquastat. I have called Hydrotherm they say call Honeywell. Honeywell say its discontinued they have no information for a universal replacement.

The hot water tankless is disconnected as I have a gas hot water tank.

I heat most of the time with a coal stove so the only time the furnace runs is if I go away for a few days. I'm 73 retired firefighter (36 yrs) .

The furnace is in good shape hate to replace just because cant find aquastat. Do you have any Ideas for a replacement universal aquastat relay. attached is all I have on unit.

Any suggestion is welcome. I usually have to clean contacts to get it running when I use it. - J.M. 12/28/2012

Photo (left) of a Honeywell L8024B & the wiring diagram below were provided by reader J.M.

Reply: parts substitution & replacements for the Honeywell L80241048B,D triple aquastat, Wiring Diagram for Hydrotherm Duo-Service

J.M.

Contact your local heating supplier with the part number (inside the cover check that you correctly identified your Honeywell Aquastat as the Honeywell L8024B1048 (triple aquastat, also the L8024D) - that's probably all they need) from the original aquastat; there are tables of substitution and changeout part numbers and names for just about every control ever made.

I'm sure they'll be glad to help you select the correct one. In fact I'm confused that you report not obtaining help from Honeywell themselves; we have usually found that the company's technical support personnel to be informed and helpful.

[Click to enlarge any image]

I'm not sure about the L8024B series information you've received, and I understand that there is not necessarily 'universal' replacement for all applications, but in fact the Honeywell L8124 series (AQS8124B1039 or the Honeywell Multi Function Aquastat L8124B1039) can substitute for many of the controllers in the L8124 and L8024 aquastat line.

We regularly see that controller advertised as replacing the Aquastat models with part numbers L8124B1039, L8124B1021, L8024B, and L8024D. indeed it might work for you as well. Also check out the Honeywell, the L7224U Universal Aquastat controller.

Be sure to review your control and how it was used with your heating service supplier;

I would be quite surprised if they couldn't immediately give you the part you need, but if you don't have success let us know and we will research further.

The wiring schematic for the Honeywell L8024B triple aquastat (thanks to your photos) is reproduced at left.

Your aquastat, the L8024B controller, also sold in the L8024D model, is being used in your case to control a Hydro-Therm natural gas-fired heater and possibly a circulator pump; often a review of exactly how a controller is being used in a given application can make more clear just what replacement aquastat will work best.

If you cannot find a suitable replacement control such as the 8124B 1039, we may find a 'new old stock' (NOS) L8024B,D, etc. series control available from a reseller.

Reader question: Honeywell R8182D replaced three times

My Honeywell R8182d 1111 keeps tripping the red safe button. This is the 3rd unit installed, they seem to last about 5 years and quit. I installed a new aquastat control about two weeks ago. It worked fine for 2 days, then went away for 4 days and when we returned the Beckett oil burner afg was off.

[..]

If i knew what to replace I would. I'm concerned about the heating season. We use the furnace for heating our hot water ,Utica external 40 gal tank, (not tankless). can you help with your expert advice? thank you, J.& J. 8/24/2013

Follow-up:

The reader ultimately let us know that the new control had been defective. Details about this case are now

at HEATING SERVICE SNAGS

Reader Question: my bad heating system aquastat only runs after we give it a good smack

Thank you for a wonderful and informative website!We have an boiler for our radiator system in our home but it's notstarting up unless we smack the cover of the aquastat repeatedly .. andthen it clicks a few times the burner flames eventually starts up -after a few smacks.If you can provide any insight to our problem, we'd greatly appreciateit.Thank you, J.D. 11/27/2013

Reply: smacking the aquastat - things to check: loose wires, buzzing, overheating, burning, damaged aquastat control

Nice question.Where is the aquastat mounted? On the boiler itself or remotely say, on or next to the oil burner?

I ask because part of diagnosing why smacking or tapping on an electrical control does something involves figuring out what you may be jiggling in the control when you rap, tap, or smack it.

I suspect a loose wire, loose connection, failing aquastat relay, or possibly a bad connection between the aquastat's temperature sensor and the sides of the well into which the sensor is inserted.

Of course there may be some other issue we haven't thought-of - something that would be immediately apparent to an astute heating service technician.

Start by turning power off (watch out for fatal electrocution hazards) and checking that all of the connections are tight.

Don't forget to check the thermostat wires too. Also listen for buzzing relays in the aquastat.

In the aquastat photo above left I'm pointing to a relay that may be buzzing if it's failing.

While the cover is off of the control, look with care for evidence of overheating or burning around any of the wire connectors or contacts At below left are burn marks around the lower-left power-connection screw.

In my photo at above right I'm pointing to burn marks on the printed circuit board of a Honeywell L8124A aquastat on the reverse side of the overheated wire connection terminal shown above-left.

This aquastat was behaving erratically for a year or more before a sharp heating service tech from Bottini Oil (Poughkeepsie) spotted the damage.

We replaced the control.

Some contemporary aquastat wells are smaller in internal diameter (often 3/8' ID) than those found onsome older boilers (sometimes 1/2' or 3/4' ID) and are typically 1/2' or 3/4' in nominal spud thread or tapping diameter and in varying lengths, comprised of brass, copper or stainless steel, also referred to as insertion wells or shells.

Oil Burner Short Cycling Traced to Poor Aquastat Temperature Sensor Contact: use the heat conductive grease

We have observed occasional short or sporadic oil burner (and some gas burner) 'on' cycles that were hard to track down. Technicians even replaced aquastats on a test system we've been monitoring, only to have the problem continue.

Way back we traced the burner on cycle problem to poor contact of the aquastat's temperature sensor in the sensor well.

After assuring that the problem was not in the room thermostat, that there were no loose wires, that the aquastat relay was working normally and in fact that the whole aquastat was new, it was following the manufacturer's installation instructions to use a heat-conductive grease in the aquastat sensor well that fixed the problem.

See these additional details that could explain why your aquastat is not sensing boiler temperature properly, now found in the article listed just below - on using heat conductive compound.

Do we need that heat-conductive grease in the aquastat sensor probe well?

This topic has moved to AQUASTAT SENSOR PROBE HEAT CONDUCTING COMPOUND

Free Up Aquastat Temperature Sensor Probe Stuck in Old Thermal Grease

This discussion has moved to AQUASTAT SENSOR PROBE STUCK in the AQUASTAT WELL

..

Continue reading at AQUASTAT RESET BUTTON or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see AQUASTAT DIAGNOSTIC FAQs questions and answers about diagnosing an repairing heating boiler aquastat problems

Or see this

Article Series Contents

• AQUASTAT CONTROLS - home
  • AQUASTAT L4006, L4006E, L4007 HONEYWELL GUIDE [PDF]
  • AQUASTAT L6006A, HONEYWELL [PDF]

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Technical Reviewers & References

• Thanks to Bottini Fuel service manager Ron Thomas for discussing aquastat functions, low limit controls, oil burner short cycling causes, and boiler maintenance, reliability, and service contracts 4/13/2010. Bottini Fuel is a residential and commercial heating oil distributor and oil heat service company in Wappingers Falls, NY and with offices in other New York locations. Bottini Fuel, 2785 W Main St, Wappingers Falls NY, 12590-1576 (845) 297-5580 more contact information for Bottini Fuel
• Thanks to reader powderfinger5 for careful reading of this text and suggesting clarifications - August 2011
• Thanks to reader Gary (Buddy Cat) for careful reading & editing - November 2012
• Honeywell Corporation, control installation guides for Honeywell aquastats and other heating and cooling controls: see http://customer.honeywell.com
• Honeywell L4008E Aquastat high limit,manual reset, aquastat controller instructions
• Honeywell L4006, Manual Reset Strap-On Aquastat (high limit control, 100 to 240 °F) [we consider strap on controls less accurate and reliable than immersion type sensor controls; these were commonly found on older heating boilers including the GE series downfired boilers]
• Honeywell L4026B Aquastat control instructions (contact Honeywell Corporation) Here is some basic description of the Honeywell L4026B control, also available at www.honeywell.com
• L7224U1002- is a universal electronic aquastat (replacing over 40 other aquastat models) that provides circulator, burner and boiler temperature control with electronic temperature sensing. The L7224U1002 provides status and diagnostic information through an LED display to enhance the diagnostic process.
  In 'Run' mode the LED displays the boiler temperature followed by the ambient temperature. Buttons inside the control permit the service tech to scan through the control's settings as well as to change them, much like the functions on a programmable room thermostat. Using the 'I' button, the LED display can be cycled through: boiler temperature, high limit, low limit, high differential, low differential, local thermostat status, EnviraCOM thermostat status, Burner status, Circulator status, Zone control, Zone request, Error code, °F/degC.
  Five diagnostic LEDs inside the control provide additional diagnostic features, indicating (counterclockwise from upper left) EnviraCOM network active, Thermostat calling for heat, Burner on, Power to zone circulator interrupted (lockout), Circulator powered.
  This is a 'triple aquastat' providing High, Low, and circulator controls, as well as advanced features permitting electronic configuration and an LED display for diagnostics. This aquastat can provide multiple zone control as well. The L7224U1002 supports Honeywell's EnviraCOM™ communications that permits remote diagnosis as well as OnWatch diagnostics. The low-limit can be disabled for 'cold-start' boiler applications such as where no tankless coil is in use.
• Eight error codes: 1=sensor fault (check sensor), 2=ECOM fault, check EnviraCOM wiring, 3=Hardware fault, replace the control, 4=B1 fault, check B1 wiring/voltage, 5=Low line voltage, check L1/L2 110VAC, 6=Fuse, check ECOM wires, replace fuse, 7=EEPROM limit and differential settings, restore to desired settings, 8=Repeated B1 fault, (voltage present at B1 when output is turned off); check B1 wiring/voltage
• Honeywell link for a powerpoint training session on this aquastat: http://customer.honeywell.com/NR/rdonlyres/5C67D10A-631C-4404-9149-25BA61F5D8BB/4041/L7224UUNIVERSALAQUASTATTrainingModule.ppt

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
• Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
• National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
• The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
• Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
• The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
• Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
• 'Residential Steam Heating Systems', Instructional Technologies Institute, Inc., 145 'D' Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
• 'Residential Hydronic (circulating hot water) Heating Systems', Instructional Technologies Institute, Inc., 145 'D' Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
• 'Warm Air Heating Systems'. Instructional Technologies Institute, Inc., 145 'D' Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
• Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
• Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
• Installation Guide for Residential Hydronic Heating Systems
• ..

• Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
  • The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
    Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page 'Promo/Redemption' space.
  • TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates
    Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page 'Promo/Redemption' space.
• The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
  Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page 'Promo/Redemption' space. InspectAPedia.com editor Daniel Friedman is a contributing author.
  Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones.
  Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page 'Promo/Redemption' space.
  Building inspection education & report writing systems from Carson, Dunlop & Associates Ltd
• Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
• Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
• Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
  Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page 'Promo/Redemption' space. InspectAPedia.com editor Daniel Friedman is a contributing author.
• The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones