Q&A on what to do when the heat won't turn ON.

This article series provides a simple sequence of steps in the order that is most likely to succeed, starting right at the wall or room thermostat and continuing through making sure there is electrical power and fuel.s.

No-Heat Diagnosis Q&A

These questions and answers about where to start if the heat won't run were posted originally at HEAT WON'T TURN ON - be sure to review the step by step procedures given there.

On 2020-02-04 by (mod) -

Scott

Post a photo of "the box", one of the "box" with cover off, one of any labels or markings, and one from more distance so I can see its location and wiring; You can only post one photo per comment so you'll need to comment multiple times

On 2020-02-04 8 by Scott

Thank you for this, the box is located on the back side of the furnace about 2 feet above the burner

I agree, it sounds exactly like a loose wire/bad connection, but when I took the cover of the box, there appears to be only one wire which connects to that unit and goes into the side of the furnace. I am sure this is the box that controls the starting of the furnace once the thermostat drops to the appropriate temperature,

I just don't know the "technical" name for it. It looks like a simple replacement, I just don't know what to call it when searching for one.

On 2020-02-03 by (mod) -

Scott

That sounds like a bad heater control unit, limit control, or if the "black box" is right on the oil burner, it may be a failing transformer.

Ask your heating service company to look again; a bad room or wall thermostat - mounted in the rooms you occupy, not at the oil burner - would not have the slightest idea that somebody was tapping on the furnace controls.

However something as simple as a loose wire connection might respond to tapping. It'd be a shame to start replacing parts before we even know where the problem lies.

Perahps you can use the "add image" button to show me the part about which you ask. One image per comment.

On 2020-02-03 by Scott

I have a Gemini Oil fired forced air furnace about 20 years old. There is a small box on the back of the furnace about 1 1/2 inches wide, 1 1/2 inches thick and about 6 inches long.

The 2 wires from my thermostat connect to the bottom of the box.

Lately, about half of the time you want the furnace to come on you need to tap this box with your finger and the furnace usually starts right away and seems to work fine. Had our oil provider in to look at it, they cleaned the furnace and said the problem was the thermostat, put on a new thermostat and still have the issue.

The furnace service tech says they no longer make the box that I believe needs to be replaced.

Do you know the proper name of this box and is it still available? Thank you

On 2020-01-23 by (mod) - My older non digital thermostat will not work or come on what could it possibly be?

Linda,

If the thermostat does not turn up the heat, let's start diagnosing right at the heater -

Is power on to your heater?

Is there fuel?

Will the heater run if the thermostat wires are disconnected at the heater and the two T T terminals jumpered together?

See detailed diagnostic steps on this very page - above.

On 2020-01-23 by linda

My older non digital thermostat will not work or come on what could it possibly be

On 2019-11-14 by (mod) -

Chris

There may be a failing relay in the heater itself, and now that you have less heat, the relay may be staying off; often there are several heater elements, turned on as needed; I suspect one or more of yours are burned out; I think your heater itself needs repair.

On 2019-11-13 by Chris

Have a 1995 Oakwood MH with electric heat. Sometimes the heat does not click on automatically although the fan does. Usually switching thermostat off and back on will cause heat to finally come on.

Replaced Thermostat 3 weeks ago hoping that was the problem but did not help. Have also noticed a decrease in heat actually blowing from vents. warm but not hot.

On 2019-11-07 by (mod) -

Tina

Is this a heat pump or only an air conditioner?

If it's a heat pump the control to switch to heat could be damaged or
if it's very cold out your backup heat may not be working - is that electric, gas, oil?

On 2019-11-05 by skyetina@yahoo.com

I have central heating/cooling ac works fine. Switched it to heat but the heat will not come on I have a manual thermostat.

On 2019-03-29 by (mod) -

Ed that sounds like a short circuit in the wiring or a motor that's seized.

What did you find?

On 2019-03-19 by ED

The house circuit breaker kicks off for the boiler

On 2018-10-25 by (mod) - old Rheem 3204-100JDA HVAC

I would start by checking that the wires themselves between the thermostat in the control or continuous and have zero resistance on individual wires.

On 2018-10-25 2 by Brad

Start of cold season and furnace wouldn't come on when set to "Auto." Furnace works fine when set to "On" at thermostat. Replaced Limit switch, Fan Center (relay replaced twice) and thermostat.

Wired blower motor from "Medium" (normal heat speed) to "Low" speed. None of these measures helped.

I have an old Rheem 3204-100JDA HVAC. Thermostat is Honeywell TH8320UP programmable thermostat. Furnace has a Limit Control, Fan Center (i.e. 24v Transformer / Relay) and there's a

Honeywell "wire saver" converting 4 to 5 wires to support necessary Common for Thermostat.

Any ideas on how to isolate the problem? thanks!

On 2018-10-25 by (mod) - furnace wouldn't come on when set to "Auto."

I would start by checking that the wires themselves between the thermostat in the control or continuous and have zero resistance on individual wires.

On 2018-10-25 by Brad

Start of cold season and furnace wouldn't come on when set to "Auto."

Furnace works fine when set to "On" at thermostat.

Replaced Limit switch, Fan Center (relay replaced twice) and thermostat. Wired blower motor from "Medium" (normal heat speed) to "Low" speed. None of these measures helped.

I have an old Rheem 3204-100JDA HVAC. Thermostat is Honeywell TH8320UP programmable thermostat.

Furnace has a Limit Control, Fan Center (i.e. 24v Transformer / Relay) and there's a Honeywell "wire saver" converting 4 to 5 wires to support necessary Common for Thermostat.

Any ideas on how to isolate the problem? thanks!

On 2018-09-28 by (mod) - new "safety mechanism" that prevents gas from entering the house

Preventing gas from entering the house - is rather unclear to me.

What gas? Entering how? I assume we're talking about propane gas used for your heating system.

There are automatic propane gas valves and also natural gas piping valvcs available for various applications though I've not encountered them on residential LPG heating systems.

Shown here is an automatic gas solenoid valve used for natural gas and propane and LPG. This valve is normally closed and opens automatically when its coil is powered - as might happen on a call for heat - otherwise the valve closes.

This particular automatic gas valve, sold world-wiode, is produced by CPF Technocontrol, is operated by a solenoid. Contact CPF Enrico Fermi, 98 - 25064 Gussago (BS) Italy, at cpftecnogeca.com or by telephone at +39.030.3730218

Ask your service tech to tell us the product name and model.

How would turning ON a propane heater change that; unless there is a valve that was manually closed and need to be opened OR a solenoid-operated gas valve that is intended to open on a call fdor heat but that was not properly installed?

You should identify the BRAND and MODEl of your heater./ heat pump, then look at the manual that came with the equipment, find the manufacturer's technical support number, and give them a call to get this clarified. I can't make sense out of what you've been told. But of course there could be a design I've not encountered.

Let me know what you are told.

On 2018-09-28 by Katrina c.

Thank you for your reply, it is exactly how I thought it would work.

The contractor is telling me that its part of some new "safety mechanism" that prevents gas from entering the house. And then said it haf something to do with the defrost cycle because "when it runs in defrost, it reverses the Freon flow and youd be blowing cold air inside so there needs to be propane"...

This is the kind of stuff I am being told.

Still doesn't explain the fact that the blower doesnt have to run during defrost cycle while in heat mode.

And like you said, heat pumps work up until a certain outdoor temp and then switch to emergency heat.

There is also the situation if you were to raise the temperature of the house 4 degrees or more, the propane kicks in first then the heat pump taked over.

Gsz160421 condenser
Gms80805cn furnace
Capf3743c6 coil

These are the part numbers for the system. I guess as the end of the day, I just need to know if what he is saying is true or I need an new contractor. The propane tank will be installed soon. So we will see if that does indeed fix it. If so, I agree,that would be a really scrappy design. Thank you again.

On 2018-09-27 by (mod) - heat pump won't turn on

Katrina,

I can give a more-accurate answer if you tell us the brand and model and serial number of your heat pump - the indoor and outdoor units; that information is on the data tags.

*Generally*, by its very definition, an "air source" HEAT pump is capable of providing both cooling AND heating to a home.

In heating mode the air-source heat pump in essence runs "backwards" from cooling mode in that it gets to work by extracting heat from the outdoor air and pumping it into the indoor or occupied space.

The heating feature should work without giving a hoot about how much propane is in the propane tank as long as outdoor temperature is not so low that the heat pump cannot extract heat from the outdoor air.

In a *typical* air-source heat pump, the heat pump can give you heat without using the propane burner as long as outdoor temperature is around 30 degrees F or in some cases down to 25 deg. F.

Here is a quote from Trane, a manufacturer of heat pumps:

"The heat pump is effective by itself down to temperatures around 25 to 30 degrees Fahrenheit. At that point, either a gas furnace or an air handler with supplemental electric heat will kick in and help heat your home." https://www.trane.com/residential/en/resources/hvac-basics/is-a-heat-pump-right-for-my-home.html

Notice that language "by itself" ?

Only when it is just too cold outdoors for the heat pump to work should it then switch into back-up heat mode. In back-up heat mode, in essence a completely-different heating source is going to be used - in your case a propane gas burner in the air handler - to produce heat.

So if there were no propane and it were extremely cold outside - below the operating temperature range of your heat pump in heating mode - would the system switch to propane heat and of course give you nothing if there were no propane fuel.

That is a GENERAL answer.

I suppose it's possible (though in my opinion it would be a terrible design) that a heat pump could be designed so that when it switches to HEAT mode it tries to turn on a pilot light to be ready in case the burner should need to ignite in case it's just too darn cold outside. But that's a rather dubious guess.

More likely you need to talk to your contractor again and tell her that unless the outdoor temperature is below the operating range of the heat pump in heating mode, then you expect it to turn on and give you heat without using the propane burner at all. If the system can't do that something is probably wrong.

On 2018-09-27 by Katrina c. - backup heat for heat pump not working

Just had a duel fuel Heat pump installed (propane emergency heat). The a.c. works well. It started to get cool enough to try the heat. The condenser nor blower turn on. Just sounds like it is immediately trying to light the emergency propane.

The contractor told me that there needs to be fuel in the propane tank in order for the heat pump to work at all. Is this true? This would mean that if we ran out of propane, we couldnt use the heat portion of the heat pump at all?

On 2018-01-05 by Anonymous

The heat or air will not turn on

On 2018-01-02 by (mod) -

Sounds like a problem at the air handler blower. I would call for repair.

On 2018-01-02 0 by Kevin

My floor vents just started humming. Its coming from my unit in the basement. But now no heat is coming through. I have a boiler system. I just bought the house 2 days ago. I'm lost....Any ideas?

On 2018-01-01 1 by (mod) - zone valve stuck closed?

Peter

Check to see if the zone valve is opening or if it has its own circulator, that the circulator is running, then look for an air-bound heating zone.

On 2018-01-01 by Peter

2 zone gas fired/forced hot water baseboard system. Zone 1 no problem. Zone 2 no heat. 24v at thermostat. Swapped thermostats, no change. Swapped Red wires at transformer, no change. Purchased new thermostat, no change.

On 2017-09-04 y Anonymous

Just installed a heat and air system air works great was going to make sure heat worked and it won't com on

On 2017-04-18 00:30:33.926595 by (mod) -

Ray and Joan,

When the heat does not come on and the thermostat is set above the room temperature - ie. heat SHOULD come on - then we go through a series of steps, checking power at the heater, fuel, etc. given in the article above.

But the fact that your heat responded after you switched to COOL then back to HEAT suggests that the internal switch in your thermostat could have been dirty, dusty, corroded, failing.

An easy "trick" to find out if the thermostat is to blame is to remove it from the equation by removing it and simply connecting the two heat wires (usually red and white) together.

A second, less easy way to check for that problem will eliminate a problem with the thermostat wires between the thermostat and the heater control: that is to go right to the heater, find where those little red and white small diameter (low voltage) thermostat wires enter the heater's primary control. Normally they're connected to terminals marked T T or T1 T2.
If you or your heating service tech just disconnects the wires at the control and then uses a jumper wire between them, that's the same as if the thermostat had called for heat; if the heater runs the problem is in the thermostat or its wires. If the heater doesn't run the problem is with the heater or its fuel supply.

WATCH OUT: do not open heating controls where there is live voltage (120VAC or higher) as there is risk of fire or death from electric shock. Those steps need to be taken by someone trained and qualified to work with electrical equipment.

David:

From what you describe I suspect that the low voltage power to the thermostat or the thermostat wires themselves have failed.

On 2017-01-24 05:21:02.547207 by Ray

I got the same problem as Joan mentioned. What is the reason? Is it serious? Thanks!

On 2017-01-18 14:47:52.437901 by Joan

My honeywell thermostat has become cranky. I woke this morning to see that the heat was set for 70 but the temp was 63. Everything looked normal, but the heat wasn't coming on. I moved the heat up 5 degrees--still no action. I put the system on cool for a moment, then went back to heat. The heat came on. Is this a problem with my thermostat or something more serious? Thanks!!!!

On 2017-01-11 18:45:53.527155 by David

My wall Honeyweill Thermostat was not showing anything and only the fan will come on when I pus the switch to it. I put new batteries in and the light shows up, but nothing else show nor will the Heat or A/C come on. Have checked all circuit breakers and switched them off and on. Only the fan will come on.

Question: humming noise in the aquastat box

(Feb 20, 2013) Rudy--mmltrtc@verizon.net said:
hello, my hotwater baseboard furnace is hot and the top pipe is hot, but the pipe coming from the circulating pump gets cold when the furnace is not working. I had a plumber come over and he hit the furnace on/off switch several time to clean the carbon off the points, it work for a day or so. the aquastat box makes a buzzing/humming noise.

Reply:

Check for a failing low voltage relay - search Inspectapedia.com for LOW VOLTAGE TRANSFORMER or LOW VOLTAGE RELAY to see more details.

Question: what to check when one heating zone won't work

(Nov 4, 2014) Anonymous said:
Well Mclain 2006 model CGi boiler with 4 zones. Problem- 3 out of the 4 zones work well. 4th zone when you turn on the thermostat the furnace pulsates and there is a click sound coming from the control module.

Boiler control module model 1107-1 lockout led's flash alternately POWER PRESS SWITCH and TSTAT/CIRC Led

Parts that we already replaced- thermostat, honeywell motorized switch(checked valve it appeared to work) and Weil Mclain Integrated boiler control module.

Nothing worked. What do I check next?

(Nov 9, 2014) Anonymous said:

Ran a new thermostat wire yesterday. Didn't work. will try connecting the thermostat terminals at the zone valve.

Reply:

Anon

Have you checked that the thermostat wiring is intact - or have you eliminated the thermostat from the situation by connecting the thermostat terminals at the zone valve?

Question: York dial thermostat trouble

(Nov 14, 2014) Anonymous said:

I have a york dial thermostat and all of the functions work, except for when on heat....any suggestions would be greatly appreciated...Thanks in advance!

Reply:

Check for a loose, corroded, or broken thermostat wire; check that there is power to the heater.

Question: tapping on the control box will start the furnace

(Jan 6, 2016) Todd said:
My furnace won't come on when calling for heat. I have checked everything electrical from the thermostat to the circulator pump.

Continuity all the way through.when touching the thermostat wires together or turning the thermostat to a higher temp,the limit switch pulls in but, won't turn the furnace on. The furnace will come on when it cools down enough for the low limit switch to start it's cycle and there is heat. It seems as though the reset box/button has a short or something.

As if I tap the box it starts the furnace at any time. Could this be my problem? Do I need a new reset button?

Reply:

Todd:

Check for a loose or corroded wire or wiring connection at the controls. Another possibility is a failing relay in the primary control box. The reset button itself isn't replacable - though that whole control can be exchanged.

I'm assuming this is oil heat: do not keep pressing the reset button. If you press it once and heat runs for 15 minutes or more you can press again and limp along until the repair tech arrives. Frequent pressing of the reset button risks a puffback explosion at the oil burner. - See more at: https://InspectAPedia.com/heat/No-Heat-Diagnosis.php#sthash.ZmcrFtz8.dpuf

Question: have power but no heat

Feb 16, 2016) Anonymous said:
I have high And low voltage at primary control but system not firing up

Reply:

Check the heater/burner reset button or reset button on the primary control

Question:

(Feb 16, 2016) Anonymous said:
I have a fuel oil furnace that won't turn on but has high and low voltage at primary control, have jupered w to r still nothing. Did notice some fuel leaking around solenoid valve,all other components individual tested OK

Reply:

Fuel leak means air in the oil lines that means improper burner operation, sooting, and ultimately either the system going off on safety reset OR worse, a PUFFBACK EXPLOSION - search InspectApedia for that phrase.

Press the reset button ONE TIME. IF the system doesn't run it's time to call for a service tech.

IF the system tries to run but doesn't check fuel, filter, and burner adjustments.

Question: Lennox oil furnace, Beckett burner, sometimes burner won't ignite

(May 4, 2016) Rick said:
i have a lennox oil furnace with a beckett burner,occasionally the burner will not ignite, but will start after pushing the reset button.

The furnace will run for several days ,then it wont ignite or it might be just one day and it wont ignite.also the blower fan comes on and wont shut off after the burner has not ignited.

The electrodes have been replaced,everything else seem to be running ok when it is working,then after a while it will not ignite.

Gets frustrating as i never know when it will not ignite and then i have no heat ,just cold air blowing.

Reply:

Rick, you can search inspectapedia for

OIL burner repairs

Oil burner goes off on reset

Oil burner won't start

To see articles on diagnosing no-start problems. From just your etext I can't say what's wrong.

Question: No power from the controller to the motor or transformer, power coming in

(Oct 5, 2016) Leon & Midge Crookshanks said:
No power from the controller to the motor or transformer, power coming in

Reply:

Check the power switch for the heating system and to the transformer - if there's power there and if the system is not off on safety reset, I suspect an open wire or a bad control board

Question: how to get heat from an old-fashioned round Honeywell thermostat

(Nov 12, 2016) Tory said:
I have the old fashioned round Honeywell but I'm not really sure how to work the Heat. How do I adjust it and turn it on and off? I don't see an on/off button

Reply:

There is no on-off button at that thermostat. Just set the thermostat dial to a point above room temperature and the heat should go on. If not check that the electrical switch for your heater - at the heater - is on.

...

Continue reading at HEAT WON'T TURN ON for the first things you can check, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these no-heat procedures:

No Heat from a Forced Hot Water Heating Boiler or Steam Heating Boiler

See NO HEAT - BOILER

No Heat from a Forced or Gravity Warm Air Heating Furnace

See NO HEAT - FURNACE

No Heat from Heat Pumps and Air Conditioners:

See AIR CONDITIONER WON'T START (also for heat pumps)

Suggested citation for this web page

HEAT WON'T TURN ON FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING SYSTEMS

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