Heating boiler problem diagnosis and repair FAQs:

Questions & answers about first steps to take when your heating boiler is not working.

This website answers questions about all types of heating systems, advising on troubleshooting, inspection, diagnosis, and repairs. We describe how to inspect, troubleshoot and repair heating and air conditioning systems to inform home owners, buyers, and home inspectors of common heating system defects.

Heating Boiler Diagnostic FAQs

These questions & answers about troubleshooting or fixing a heating boiler (hot water heat, hydronic heat, baseboards, radiators &c) were posted originally

at DIAGNOSE & FIX HEATING PROBLEMS-BOILER - home. Be sure to review that article.

On 2017-09-11 by (mod) - should the water supply to the boiler be ON

Frank:

In most residential hot water heating systems the heating boiler has its own water supply line and control valve and pressure reducing valve to automatically feed water into the boiler should some leak out.

The boiler and its piping are a closed system that gets filled when installed and that is normally always full and should not use water (unless it's a steam system).

IF your boiler has ONLY a manual water feed valve AND PROVIDED it is a HOT WATER or HYDRONIC boiler NOT a steam boiler, then you should ask your heating company about installing a pressure regulator and water feeder.

Separate from the heating boiler that's heating your home (just described) is a tankless coil used to make domestic hot water for washing. The tankless coil has its own cold water inlet and hot water outlet that supplies water to the house.

The tankless coil absorbs HEAT from the physically separate hot water inside the boiler and transmits that heat into the water entering the coil from your building water supply system and flowing out of the coil to give hot water at plumbing fixtures.

The coil normally always has its water supply on or open - else you'd have no hot water.

Use the search box on any InspectApedia page to find our article series on TANKLESS COIL FOR HOT WATER to read details.

Watch out: most pressure/reducer - water/feeder valves come with an instruction sheet that specifically says the valve is a pressure reducer NOT an automagic water feeder even though everybody uses them for that purpose.

I have found that aftoer 20-40 years of service a typcial pressure-reducer valve like the 1960's B&G Pressure Reducer shown here become clogged and stop feeding water to the boiler.

In that case the valve won't keep the boiler at 12 psi cold and you'll need to replace the valve.

On 2017-09-11 18:42:32.938045 by Frank

I have a Peerless oil burner. it has a tankless heater. My question is is my intake water supply suppose to be turn on. and turned off when the boiler is full? Or does the water stay on all the time the boiler is on. My brother couldnt remember which level he turned for the winter.

If I leave the water on will it flood the boiler. I have forced hot water heating. And I have and electric water heater, I dont want to turn on the water and flood the boiler.If the water stays on will it damage the boiler? Boiler WB-3 Water 30psi. boiler no.wb-110-wpc

On 2017-08-08 00:40:43.330059 by Jeana

My water level in my boiler went below the low water cutoff. Now we have no hot water from the tankless water system. How do i get it fired back up? Water level is up. Circuit breaker wasnt tripped. No reset light on....

On 2017-04-01 22:57:53.007924 by (mod) -

Athens

I'm sorry I can't be of more help but I just don't understand enough about your system from your question. I've ever in the article above Iris a sequence of steps that you can follow to check a common causes for loss of heat you might take a look at the safety reset button on your burner control if it's an oil burner.

On 2017-04-01 17:07:02.279469 by Athens

Water boiler sister will not turn on. Zone valve is hot when on and the gears in the zone valve move when you turn switch on and off. Pilot light is on wires seem to all be fine and we were only working on one zone valve not 2. This is only the 5th season we have used it.

On 2017-03-20 18:10:43.775724 by (mod) -

If your hot water is made by the same boiler than we can figure the boiler runs ok - in that case the problem will be with a circulator (s) or controls or relays, or perhaps air blocked heating pipes. I'd look through the steps and suggestions in the article above; then follow-up with more detailed looks at the components those diagnostic steps suggest.

On 2017-03-20 11:17:15.074887 by amy

no heat but have hot watet olil boiler

On 2017-03-06 01:58:31.808555 by Purvishankerson@gmail.com

OK well I have hot water but no heat.i think it's propane. Not understanding why it's not heating, could it not be little?

On 2017-02-21 23:45:29.931174 by (mod) -

This sounds to me like an improperly-wired or set aquastat. Search InspectApedia.com for AQUASTAT SETTINGS to see details.

On 2017-02-21 20:24:06.620001 by Steven

I have a boiler that when thermostat calls for hear ( nothing) but when I run the hot water, heat will start circulating, but only when hot water is running.

On 2017-02-21 16:39:42.694295 by (mod) -

I think something's wrong with your heating system, Keith. Look for a loose or corroded electrical connection in the thermostat wiring.

If your system is typical it's the room thermostat that turns the circulator on or off, not the boiler water temperature.

But your guess makes sense in another vein: check that the LO on your aquastat is at least 20 degF. below the HI = otherwise cooler boiler temperature will indeed turn off the circulator. Read more details about those settings by searching inspectApedia.com for AQUASTAT SETTINGS

On 2017-02-21 12:56:11.714897 by Keith Stamper

I would like to know why when the heating cycle begins does the circulation pump cut in and out multiple times before running continuously. I t seems to me that the flow of heated water begins once operating temperature is reached and then the pump runs for about 10 seconds and stops before repeating this cycle.

Eventually after about 10 cycles the pump runs continuously. I suspect the return of cool water to the boiler causes this stop/start cycle until the heated water has completed a circuit of all radiators in the house. I am considering calling someone in but don't want to do this unless these is a fault.
Thanks,
Keith

On 2017-02-15 17:01:19.186101 by (mod) -

N Marino:

Please search InspectApedia for AIR BOUND HEATING SYSTEMS to read the probable cause, diagnosis, and cure for the problem you cite.

On 2017-02-11 04:49:36.804864 by (mod) -

DAVE

I hope you found and tried pressing the RESET button on the primary burner control - just ONCE.

On 2017-02-10 23:00:39.363871 by N mariano

No hot water system is oil /domestic hot water. Relief vale circulator coil in burner and mixer valve have all been changed by plumber still no hot water

On 2017-02-10 13:07:57.693714 by dave

having problems with hot water heat boiler.thermostat is calling for heat but boiler will not fire off.there is power to the boiler,I can hear the circulator pump running,have oil in tank,also checked to make sure that there was oil flow to the burner which there is.even set thermostat 10 degrees higher,still nothung

On 2017-01-30 17:13:40.557873 by (mod) -

Open connection perhaps?

On 2017-01-28 21:28:57.564116 by Bill

Trinity TI150

Thermostat calling for heat. Limit and flow switches ok. Draft motor running with pressure switch provimg. Code ASC. NO power to ignition module. Result no power to gas valve or ignitor.Any suggestions what to look into next.

On 2017-01-19 13:32:40.528184 by Bob

I have no heat or hot water coming from my Weil McClain furnace

On 2014-11-20 18:21:31.715980 by (mod) -

Helder

I agree that something is wrong - an oil burner, properly serviced, ought to be able to make it through a heating season with one cleaning and adjustment - BUT if there is an external problem such as excessive sludge entering the system from an older oil tank you might still have trouble.

Take a look at

https://inspectapedia.com/heat/Oil_Burner_Puffbacks.htm

on oil burner puffbacks for some diagnosis that might help avoid a recurrence of that dangerous event

then

give your oil heat service company manager a call, explain your system's history and ask for help from an experienced heating service technician.

A puff-back

On 2014-11-20 17:00:27.181760 by Helder.

My oil Burner has to be cleaned about every two months .my smoke alarms and my common monoxide detector goes off .. I only have the house for a year and we had a puff back last year .I don't understand why you get so dirty. Please help

On 2014-10-19 20:18:12.700770 by (mod) -

Jeffro

We would welcome specific comments, criticism, or suggestions regarding the photo to which you refer. Else your comment is provocative but not so helpful.

On 2014-10-18 18:02:00.768070 by Jeffro

I saw no caption on the boiler installation at the head of this article:

https://inspectapedia.com/heat/NoBoilerHeat.htm

Are you suggesting that this is a proper installation? I sure hope not! ;-)

On 2014-10-12 16:44:43.349150 by Anonymous

Rich, Oil Burner(Energy Efficient turns on and off automatically)But now only turns on for hot water with the thermostat 20 degrees above room temp.

On 2014-10-09 23:35:26.147080 by (mod) -

Yes Bob. You can try feeling the boiler's hot water piping system and baseboards or radiators to see where the heat stops. That may give a clue to what may be air bound.

On 2014-10-09 20:54:07.734590 by Bob

The one zone heats only about 20%. The furnace is also coming on, stops, comes on again, but never reaches the set temperature. My thermostat was replaced about 15 months ago. Could it be air in my line or zone valve not opening all the way, or what?

On 2014-07-29 12:24:25.484340 by scott

message on control panel says 'internal' what does that mean?

On 2014-01-30 21:46:56.406580 by (mod) -

Charles,

check that the heating system pressure is sufficient to get water to highest floors

feel along the pipes to identify where they begin to be cold; if that zone is running I suspect that there may be air in the piping that is not being bled out at the particular bleeder valves you are opening. You may need to ask your heating tech to force air out of the system

On 2014-01-30 17:00:53.326010 by charles

not getting heat at the furthest radiators but have water at vent

On 2014-01-30 02:09:36.383060 by (mod) -

Maria,

regarding " It turns off and on at its own sporadically but never exceeds the set thermostat temperature and now has gotten to the point where the air in the room will be up to 12 degrees colder than the set temperature on the thermostat, especially when it is a cold night"

I can't quite figure that out. You say the furnace never exceeds the thermostat temp - meaning it never overheats the room - which is proper operation.

Then you say air in the room is 12 deg colder than the thermostat.

When you see cold air in the room where are you measuring it? Check the thermometer right on the thermostat - that's the air that the thermostat is sensing.

Then I read comments about radiators - so we're not talking about a furnace (warm air heat) but rather about a boiler (hot water heat) or a steam boiler (steam radiators, steam heat).

In any event the thermostat diagnosis is a good place to start.

I would not keep cycling heat off and on. That humming may be a clue that a motor is having trouble starting. OR a safety sensor is shutting off your heating system. If so it sounds as if you're past due for a heating service call.

Perhaps if you stop messing with the controls, just leave the thermostat set at one place, and don't cycle the system on and off, you can keep a log of how the system acts that will help the service technician. Or if the system shuts down, leave it in that condition and call your heating company. THat will make diagnosis a bit easier.

Keep us posted.

On 2013-02-15 02:16:58.785650 by Maria

I have an older gas furnace that generates heat for water-based radiators.

The unit does not stay on consistently. It turns off and on at its own sporadically but never exceeds the set thermostat temperature and now has gotten to the point where the air in the room will be up to 12 degrees colder than the set temperature on the thermostat, especially when it is a cold night.

Oddly, it seems to turn off more often at night, then runs during the day. It "prefers" to be set at higher temperatures, as it is hard to stay on with a range between 65-74 degrees.

After the unit shuts off, I can turn the thermostat all the way off, then if I turn it up to 74 or higher it will click back on, as evidenced by a normal light humming sound. I sometimes will turn the thermostat on and can hear it torque up downstairs, then several seconds later, no humming sound, the torque stops, and no heat is distributed.

If I keep repeating the process, after the torque and humming sound starts, then it may stay on typically for about 3 hours on a good day.

I always have to "restart" using the thermostat by 4 AM. I replaced the thermostat, and bled the radiators.

All radiators are on the same zone, and are running the same temperature to the touch. Unfortunately the unit tends to work precisely when the HVAC people come out, and they say that the problem can't be diagnosed unless the unit is totally non-operational. Please give me some ideas as to what this may be.

On 2013-02-06 00:53:31.280319 by jamie

i have an old villiant boiler. water temp won't reach over 170 degrees. i have replace burner and gas valve. gas pressure is at max at 4 inches. limit switch is set at 180 degrees therefore boiler never shuts down. what else could be wrong?

On 2013-02-04 18:56:21.156442 by miguel

Is it safe to restart my boiler if the water level gauge shows the level is low? I have oil in the tank but the boiler shut off.

On 2013-01-31 19:36:32.940904 by john

have hot water but no heat. my home uses a Slant Fin GXH-105 gas boiler for hot water and heat. a few days ago the heat stopped working.

initially i thought it was the gas vent damper that might be acting up so i locked it in the open position. thermostat calls for heat but nothing happens. also using a honeywell triple aquastat relay model type L8124E.

when i manually connect the circulator relay it'll work. not sure if there's issue w/ the thermostat or need to replace relay. would i be able to replace the relay with a different model such as L8124A or G? thanks in advance for any help.

On 2013-01-26 04:17:28.823222 by tom

help please its cold in nh

On 2013-01-25 by Erik

Hi I have two oil burning units, one is a boiler for heat and the other is a 33 gal oil fired hot water heater.

There is one supply line that has a tee and one return line with a tee. The setup was fine for many years. After a flood we changed the water heater and the pump / blower on the boiler. Now the oil burner only starves for oil if both are running at the same time.

All filter where changed and checked to see of the shut off valves are fully open and no kinks in the line.

On 2013-01-24 by Toinette

I have a very old boiler that uses propane to heat 2 zones in my veterinary hospital. For the past 2 days, the one zone is working fine but the the #2 zone is not getting any hot water to the registers in that zone at all.

Alot of the pipes are in my attic which is very cold and here in Michigan it has been extremely cold (10 below) and the service technician was out for 3 hours looking for a frozen pipe but could not find it.

He told me to just wait until it gets warmer and the pipe thaws a bit. The problem is I run a hospital where the patients must be warm and waiting is not an option.

After he left I took it upon myself to investigate (or diagnose in my case) and one thing seems very odd. I have 2 pipes that exit the heating unit and they both are hot coming out of it which makes me believe that portion is working.

We then come to a pump on each line and the pumps are hot as well on both. Now the pipes then go up and into the ceiling and in the attic. At the point where it enters the ceiling, the pipe for the zone that is working is hot and the pipe for the zone that is not working is cold. I followed them into the attic and again the pipes for the working zone is hot and the one not working is cold. Therefore, I thought it would indicate that the problem is from the pump to this point.

Can there be a frozen line 20-30 feet away that preventing the pump from working? I am wondering if it is the pump? How can you tell if the pump is working properly? The pumps on both look identical and I can't tell how they work or how to tell if the one is not working?

They don't make any noise when they are pumping that I can tell anyway. I would assume the technician checked this when he was there but I can't be sure. Does this make sense, or am I missing something big as I don't know anything about a boiler.

On 2013-01-24 01:24:15.692377 by Anonymous

Our boiler is used for heating only. The boiler is firing and heating up but the room temperatures upstairs is a constant 62 degrees and not able to get above that temp.

It is 5 degrees outside. We changed the thermostat, bled the radiators and removed any air, and they had hot water and we also made sure the psi was correct but still not able to get room temperatures above 62. Any ideas what might be causing this?? Thanks

On 2013-01-05 01:52:30.063213 by Anonymous

Are sight gauges still used on gas furnaces

On 2013-01-02 18:28:54.303988 by Re: Honeywell L8124A Aquastat

I suspect that the circulator pump relay might not be working, and not supplying voltage to the pump. Any ideas as to how to check if the relay is working?

On 2013-01-02 18:08:52.791277 by mike

the boiler runs and almost gets to the set temp 180 then drops down. The boiler keeps running then the pressure release valve goes off.. what can it be..

On 2013-01-01 19:46:03.586816 by Bruce

We have a boiler heating system. In one of the zones there is no hot water flowing through the baseboard heat pipe. The boiler is hot and is circulating through the other two zones. All three zone valves are open. Pressure is 20 psi(15-25 is Recommended range).

Why won't hot water flow through the zone with the pump circulating through the other two zones and all zone valves open!

On 2012-12-27 20:16:11.012310 by Laurie

I have an old Oil fired water Boiler. The house used to heat with Radiant heat through the floors as well as radiators. It also heats the water. We have disconncted the radiant flooring heat and it is only radiators now. The heat goes on for about 90 min (reached temp I assume) and then you can hear the relay clicking (sparks)

I shut the breaker when that happens. Why would it do this and I also want to say it does not get past 150' on the temp gage on the boiler. Someone said it was the Thermostat? I think relay, and someone else said the aquastat??? HELLPPPP Laurie

On 2012-12-10 22:05:02.454544 by (mod) -

Tom, I've posted your question and a brief reply in the FAQs just above.

On 2012-12-10 17:41:09.810420 by Tom

the thermostat signals but the furnace will not turn on

...

Continue reading at DIAGNOSE & FIX HEATING PROBLEMS-BOILER - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see DIAGNOSE & FIX HEATING BOILER, FAQs-2 - more-recently-posted questions and answers about how to diagnose and fix a heating boiler

GAS PIPING, VALVES, CONTROLS if your heating system is fueled by LP or natural gas

See HEATING SYSTEM TYPES if you don't know whether your heat is provided by a furnace (hot air) or boiler (hot water), or steam boiler (steam heat) or whether your fuel is oil, gas, or electric, and whether your heat is hot water, steam, or warm air

Or see this

Article Series Contents

• BOILERS, HEATING
• BOILER OPERATING PROBLEMS
• DIAGNOSE & FIX HEATING PROBLEMS-BOILER
• OIL BURNER INSPECTION & REPAIR.
• GAS BURNER FLAME & NOISE DEFECTS
• GAS BURNER SOOT CAUSE & CURE
• GAS BURNER PILOT LIGHT PROCEDURE
• RADIATORS for ROOM HEAT - topic home, for cold radiator or baseboard diagnosis and repair

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DIAGNOSE & FIX HEATING BOILER, FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING BOILERS

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