FAQs#2 :diagnose & fix a room thermostat that that won't turn the heating or cooling system ON

This room thermostat diagnosis and repair article series provides a sequence of diagnostic steps that determine if the problem is at the thermostat, the thermostat wiring, or at other heating or cooling system controls.

FAQs: heating or cooling system won't turn ON set #2

These questions & answers on fixing a thermostat that won't turn on heating or air conditioning were posted originally

at THERMOSTAT WON'T TURN ON - be sure to see that diagnostic article.

But if it's not a thermostat problem see HEAT WON'T TURN ON

On 2018-11-27 by (mod) - how to test thermostat wires when thermostat won't turn on or off the heat or A/C

Richard

I would start by checking the actual wires that run from the thermostat to the heater.

Disconnect the wires at both the thermostat and at the heater.

Test for shorted thermostat wires

FIRST with both ends of both wires disconnected, at each end of the pair check for continuity between them (use a VOM or DMM).

If you see continuity, since the wires are actually disconnected at the other end from that where you're testing, we can bet that they're shorted together enroute - probably this is NOT your case so

Teste for broekn thermostat wires

NEXT at one end, tie the two thermostat wires together

At their other end, check the wires for continuity.

That will tell us if the wires themselves were broken enroute.

See any of these articles

• ANALOG VOMs & MULTIMETERS
• DMM DIGITAL MULTIMETER HOW TO USE
• DMMs VOMs SAFE USE OF
• DO IT YOURSELF ELECTRICAL WORK
• TEST EQUIPMENT, ELECTRICAL

On 2018-11-29 by Richard J Schlogl

My electric heating system does nor respond using thermostat. Tha main switch on the system will turn the heat on/off but the thermostat has no effect.

It started with old thermostat not responding for short while then is fixed itself. I bought a new thermostat but it also does not work. All my celebrations seem to be correct. I'm presently using the main on/off switch. Help?

On 2018-11-27 by (mod) -

Rosenarue

You can also check some easy do-it-yourself diagnostics at

HEAT WON'T TURN ON

Where we describe typical problems when the issue is not the thermostat. Examples would be making sure that you have fuel and that power is on to your heating system.

On 2018-11-27 by Rosemarie

(November 27, 2018) Rosemarie said:
I should add that those examples of time where I stated previously I hear the furnace running, but there is no heat.

After a few minutes the furnace sound does turn off.
Same as when I go to the Set to make changes, the furnace sound does comes on but in a few minutes it does shut off.
So it is off now and again at 63 degrees as it was this am saying Heat On, however no furnace sound and no heat.

(November 27, 2018) Rosemarie said:
Didn't post date on last comment. I should add that the thermostat stays at 63 degrees and it says Heat On, however, furnace is not running and there is no heat.
I took the face plate off and put back on moving left and right gently as explained on a site. Now, I hear the furnace which is in the attic run, but no heat. If I go to set to
correct time, etc. again I hear furnace upstairs, but no heat. I did switch the fuse box as well. Unfortunately, it also says in tiny letters "Leave" and I have tried to
reset that to "return" but always shows "leave" anyway. Again my question is should I until someone comes by to check it, turn the thermostat to Off?

someone is coming over tomorrow to see why my Honeywell thermostat is staying at 63 degrees, no heat.
I changed batteries, still not working.
Meanwhile is it dangerous at this point, should I turn the thermostat to Off?

On 2018-11-15 by (mod) - Is it a heat pump? First confirm that your AC system is also a capable of delivering the heat.

John,

First we need to confirm that your AC system is also a capable of delivering the heat. If it is make sure your thermostat is set to heat low. If you're in heat mode and the temperatures are high enough that the heat pump should be running and it does not then there's a problem with the control board or thermostat wiring.

If outdoor temperatures are lower than your heat pump can use your system should be switching to backup heat.

On 2018-11-15 by John

Hi I have a slight problem I have a Honeywell I have central air and oil I'm getting cool air and I'm trying to get heat need help

On 2018-11-12 by (mod) - check jumpers or DIP switches on the control board for backup heat

Check if there are jumpers or dip switches for the blowr fan on the control board for backup heat

Check for a bad fan limit control

On 2018-11-12 by Franklin - in heat mode blower motor doesn't turn on

Please help I'm lost

Alright check it out.. T-stat is good sending signal to turn on a/c that's fine But when in Heat mode The blower motor doesn't turn on every thing else works like the inducer and igniter and burners turns on except blower motor brand new unit

On 2018-10-27 17:10:11.203281 by (mod) -

Fred

Let's start debugging this right at the furnace. Disconnect the thermostat wires at that end and then jumper the two thermostat terminals. If that turns on your heating system and it works correctly then we have identified that the problem is either in the thermostat wires running through the building or at the thermostat installation that you've made at the thermostat wall location.

On 2018-10-27 03:13:13.231971 by Fred

Took thermostat off wall drew a diagram of wire settings . Furnace won't work got new thermostat still won't work. Am at wits end. Someone please help.

On 2018-01-26 by (mod) - King Wall Thermostat: digital thermostsat controlling line voltage heaters

Carol,

FYI, the King Electric Electronic 208/240V 22Amp Digital Line Voltage Thermostat, is described as: 3 Wire Leads, 40F - 95 F, Backlight Display, ON/OFF illumination switch, System OFF switch. I include, for other readers, a photo below.

The thermostat, in default mode, should be displaying the room temperature.
When you press an up or down key, a thermometer appears in the display, and you can then further press up or down keys to change the SET temperature for the room.

If your thermostat is reading 88 degF before you touch it, it thinks that's the room temperature.

A thermostat might read higher than the actual room temperature for a number of reasons such as where it is located, exposure to sunlight or to another heat source.

I would start by making an independent check of the room temperature, maybe mounting a simple thermometer right next to your wall thermostat.

Information about electric heat thermostats including the King model you describe is found at THERMOSTAT WIRING ELECTRIC HEAT inspectapedia.com/heat/Thermostats_Line_Voltage.php

Carol

You can contact the company directly for help at

King Electrical Mfg. Co., 9131 10th Ave. South, Seattle WA 98108, USA, Tel: 206-762-0400, Website: www.king-electric.com

On 2018-01-26 by Carol

A few months ago we installed an ES230-R 240/208 Volt Digital Thermostat to control 2 King electric wall heaters. At bedtime we turn the thermostat down to 62 from 72.

Occasionally, when we go to turn the thermostat up for the day, it will be reading "88". By pressing on the up button for a few seconds, I can turn it up to 72 and it will work fine. Can this happen if the house temperature went below 62 during the night?

On 2018-01-19 by rogan994

just something to look at and try if your thermostat is new or u tink maybe the old one is still good, i work maintenance at an apartment complex in florida, not usually a need to run heat, and most of the ppl that live there never run it except for the past couple weeks while its 20+ degrees at night, so i looked at the old thermostat, the back of it has a switch u can flip to set for either gas or electric heat pumps

, it was in gas and all of ours are heat pump/electrical heat ..flipped it from gas to electric and that fixed the problem..went from blowing cold air to hot..

had another one blowing cold halr when therm was set to 78-80, therm was actually bad, i put in the new one and it had 3 switches on the back of the computer board, thought i switched them all, connected everything turned breaker back on, and still no hot air only cold..took it back apart to look again,

and i forgot to flip the switch on the back of thermostat from “norm” to HP..was on norm and that ran a normal furnace/ac..(im assuming by normal that emplys gas furnace and even the outside unit wouldnt not come on.), flipped that switch to HP, (electric heat pump) and within 15 seconds the outside unit came one and it was blowing HOT air..

problem solved..now not sayin this is an all time fix. or what is wrong with urs. BUT, def worth looking at if ur having issues with ur heater blowing cold air..

On 2018-01-12 15:48:32.585798 by (mod) -

Check that the furnace burner actually starts. You may be just turning on the blower fan

On 2018-01-12 15:48:13.365136 by (mod) -

Check that the furnace burner actually starts. You may be just turning on the blower fan

On 2018-01-12 00:23:59.434877 by Geo

The furnace wont start on Auto but will run on On ..... ?

On 2018-01-04 00:44:54.396752 by (mod) -

Musty

At NO HEAT, FURNACE https://inspectapedia.com/heat/Furnace-Diagnosis-Repair.php

You will find a sequence of basic steps to take. Try that and let me know how that works for you.

On 2018-01-03 08:13:12.180574 by Misty

My furnace in my fifth wheel was working just fine this a.m.the thermostat was replaced with a new one 4 months ago!now it won't turn on at all!No heat no fan no ac,

nothing happens.just quit all the sudden.my stove lights up just fine.the refrigerator works fine and I'm plugged into an outlet so I should be getting plenty of juice.can anyone tell me what the heck the problem could be?

I'm freezing to death. I have a 2000 5th wheel that's 35 feet long with 3 slide outs.i have an informed heater in the living room n its just not enough to keep up the heat without the heat running.ive tried to turn the thermostat off for a bit to see if it will reset.but no luck there

.its like the thermostat just died on me all the sudden!very frustrated and cold lol..sincerly misty

On 2017-12-19 13:23:43.745964 by (mod) -

Judy

Perhaps you can tell us the brand and model thermostat, or use the tiny picture frame icon to the right of the Comment button to open a comment and insert a photo of the thermostat and I can comment further.

Some thermostats might have an upper set temperature limit, or it may be that instead of pushing the UP button you need to hold it depressed for a few seconds.

On 2017-12-19 06:01:00.400479 by judy

I rent an apartment. Heat is included in the rent. Brand new thermostat. the right side of the therno says 70 degrees. Ok, so I'm cold and want to turn the heat up higher to: 74 degrees. I keep pushing the button to go up higher. It won't go higher. It only to goes to 70. It is cold in here. Could the landlord have the furnace set up to go only up to 70 degrees? What and how does he do that? Is it in the furnace ? The furnace is downstairs, where u cannot get to it. Please let me know, What is the problem. and can he do this, so we don't get much heat?

On 2017-12-04 14:15:32.402819 by (mod) -

Josh, when you have no teeth at all and the heating system is not turning on you want to start with the NO HEAT diagnostic procedure at

https://inspectapedia.com/heat/No-Heat-Diagnosis.php

On 2017-12-03 04:15:27.023113 by josh

The thermostat that turns on the circulation pump for baseboard heating is not clicking and the pump doe snot come on so there is no heat in the baseboard

On 2017-11-29 22:38:32.673360 by (mod) -

Betty, did you try the diagnostic steps for no heat found at

https://inspectapedia.com/heat/No-Heat-Diagnosis.php

On 2017-10-29 02:26:18.212184 by Betty

Me again,I wouldn't bother you tonight except it's cold. Thank you for help !

On 2017 10 29 Mod said: the heater won't turn on and I don't think it's the thermostat

Betty, please see the diagnostic suggestions starting at HEAT WON'T TURN ON and let me know what further help you need.

On 2017-10-29 by Betty

Me again,I wouldn't bother you tonight except it's cold. Thank you for help !

My heater won't come on. I changed batteries, there's a reset spot...what should I do? The brand is Hunter,digital.

On 2017-10-28 by Ronald kuhaneck

My Yoak 5 ton turns off on

On 2017-08-20 by (mod) - where to find instruction manuals for heating and air conditioning equipment

Sure Vlad.

You can find Fujitsu Manuals including for the control, operation, and wiring of the ARG30ALC inverter at

FUJITSU ROOM AIR CONDITIONERS

On that page you'll find a link to the Fujitsu Manuals, and there you'll want

FUJITSU AIR CONDITIONER DESIGN & TECHNICAL MANUAL R410A [PDF] Inverter, Indoor & Outdoor Units including Compact Cassette AUU9-12-18RLF, Slim Duct ARU9-14-18-124RLF, Compact Wall Mount ASU7-9-12RLF, Wall Mount ASU18-24RLF includes wiring diagrams

where you'll find a live link to that file as a PDF

On 2017-08-20 by vlad

@Ayub,
Hi Mr Ayub, Can you upload the drawings (Circuit diagram) of the O'General Duct Thermostat, Model No : ARG30ALC.
Thanks

On 2017-06-16 by Joyce

The heater switches on but the temp wont increase

On 2017-06-15 by Ayub

My thermostat won't start. I suspect people doing maintenance work on the rooftop have done some damage though i am not entirely sure.

I have been on the rooftop and as the building is residential there are multiple ac units for each room and i was not able to find mine. I managed to find what looked like a water pump valve with my flat number on it and right next to it there is a ac unit.

My question is,

a. How can i be sure which ac unit is for my room ?
b. Could someone accidentally switched off the power to the ac unit ?

I have a O'General Duct Thermostat, Model No : ARG30ALC.

Thank You

On 2017-06-07 by (mod) - thermostat G-wire

Ann

If the furnace never used the G-wire then I suspect all changes or jumpers ought to be handled right at the thermostat.

Let's review what your thermostat needs to control (heat only?) and to do that let's start with the brand and model thermostat so we can take a look at the installation instructions.

I also need to know just what thermostat wires are

1. present coming out of your wall at the thermostat

2. present and connected to anything at the other end of the same wire set at your heater

Also see the jumper wire instructions found

in COMMON WIRE at THERMOSTATS

On 2017-06-07 by Ann

I got a new Wi-Fi thermostat and in un-installing the old one I did not have a C wire.

The instructions stated to put the G wire into the C-wire spot then open the furnace are and switch it there also and create a jumper from the G to the Y. In opening the furnace I had wires to both C and G.

In leaving them as is the new thermostat was not coming on.

In putting the G wire into the C (And capping the C) it's on and running but not cooling.

I did do the jumper as the G and Y were not next to each other. Should I put the C in the G spot? Thus essentially switching them?

Nothing is in the G spot now at the furnace.

On 2017-05-19 by (mod) - switch on your thermostat won't change when it should

Liam

If the switch on your thermostat won't change when it should, either the thermostat is defective or there is a heating or cooling system condition and problem on its other end that we don't understand.

You're citing a Honeywell DT 92E Wireless Room Thermostat with ECO energy saving feature. That thermostat includes an Off/standby button, allowing manual switch off, with frost protection active.

Off/Standby Button, with Frost Protection

The off/standby button allows DT92 to switch off the heating (or cooling) system at the touch of a button.

To prevent accidental switch-off, the button must be held for 2 seconds to activate the change.

When off, DT92 will maintain control at a frost protection setpoint, factory set to 5°C but adjustable between 5 and 16°C.

If required, frost protection can be switched off, to provide a positive off function. These adjustments are made by entering the DT92 Installer Mode.

See this HONEYWELL DT 92E THERMOSTAT SPECIFICATIONS sheet at inspectapedia.com/heat/Honeywell-DT92-Thermostat-Specifications.pdf

and

See this HONEYWELL DT 92E THERMOSTAT INSTALLATION MANUAL inspectapedia.com/heat/Honeywell-DT-92-e-Thermostat-Manual.pdf

Both of those are PDF files also available directly from Honeywell

On 2017-05-19 by Liam

My DT92E thermostat seems to be stuck on standby

 

...

Continue reading at THERMOSTAT WON'T TURN ON or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• AIR CONDITIONER BLOWS WARM AIR
• AIR CONDITIONER WON'T START
• HEAT WON'T TURN ON
• THERMOSTAT WON'T TURN OFF

Suggested citation for this web page

THERMOSTAT WON'T TURN ON FAQs-2 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 HVAC THERMOSTATS

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