Question about Heating & Cooling

2 Answers

Honeywell T8000C Thermostat Problem

Came back from a vacation and found the downstair thermostat's display blank. I tried all - reset breaker, reseat the unit. The upstair system is OK. The downstair system is not operational. Took the upstair thermostat downstair, and it also went blank. Replaced it back to the upstair wall mount and it is OK. There is a heater/fan in the attic that I have not checked. TIA for some pointers...

Posted by on

  • 5 more comments 
  • ucanfixit Jan 04, 2008

    Mr. Therinnaiguy,

    It has got a bit cold lately in San Diego, so I decided to follow your advice and give it a try before calling the expert..,

    As you pointed out, a blown 3A-32V spade fuse was found!!!

    Got new one from Autozone to replace the blown one, all the voltages come back. Heater is now working again.

    You are an angel!!!! Thanks very much.

  • tosha001 Apr 22, 2008

    I have the Honeywell square thermostat and I cam home yesterday from work and noticed that the display screen was blank. The a/c unit was already off so not I cannot turn the unit back on. I have tried resetting the breakers and all, but still nothing. Please help

  • wholphin May 01, 2008

    yesterday we lost power and upon power restore, the lcd was blank on the downstairs Thermostat but the upstairs one was ok, brought the upstairs one down and it worked downstairs.

    What could be wrong with the unit in this case? Should i try to replace the fuse on the bad Thermostat? or is purchase a new one?


  • monique765 Jun 07, 2008

    I have a similar problem. My power was out for a few days and when it came on, our screen on the thermostat was blank. Is the fuse you are talking about directly on the thermostat or is it in the hvac unit? I am unsure.

  • ucanfixit Jun 20, 2008

    Sorry, I have not checked back for a while.

    The fuse is in the hvac unit. Mine is in the attic. The problem is not with the control on the wall. The panel will need to be removed in order to see the ckt board and the blown fuse.

    Good luck!

  • Perplexed411 Oct 05, 2008

    I have a Honeywell T8000c Thermostat that controls a Comfortmaker NTG3 model furnace. The Honeywell display does not work since there is no 24 volt power to the wall plate or at the circuit board of the hvac unit. The fuse is OK and the blower motor operates continuously if the furnace unit switch is in the on position. According to the manual wiring diagram, the blower operates directly off the house 115 volt power while the electronic gas ignition and the thermostat use 24 volt power from the unit transformer. Is there anything else that I can check before calling a service technician since I can't operate the furnace.

  • avery_b Dec 20, 2008

    i have a honeywell T8000C thermostat with a blank display. circuit breaker is fine and the fan is still running. what should i do?



2 Answers

  • Level 3:

    An expert who has achieved level 3 by getting 1000 points


    An expert that got 20 achievements.


    An expert that got 10 achievements.


    An expert that got 5 achievements.

  • Master
  • 1,420 Answers

If you have a volt meter, remove the thermostat off from the mounting plate and check for 24 volts AC across red (R) and White (W). Then check across Red and Yellow (Y). If you do not find any voltage, follow wire as much as you can all the way back to the air handler that is connected to it. Look inside and see if there is a small Auto (car) type of fuse in the wiring harness. Test and replace if necessary. Jump out the Red and Green terminals on the air handler and replace the door. See if the blower turns on. If so, you have narrowed it to the wiring to the thermostat. If not, you have a power problem and will need a technician.

Posted on Sep 28, 2007

  • Level 1:

    An expert who has achieved level 1.


    An expert that has over 10 points.


    An expert whose answer got voted for 2 times.

    Problem Solver:

    An expert who has answered 5 questions.

  • Contributor
  • 10 Answers

In my case the blank thermostat was indicative of a problem at the furnace. A blown limit switch to be exact due to a neglected filter.

Posted on Feb 22, 2010


1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

A 6ya expert can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
The service is completely free and covers almost anything you can think of (from cars to computers, handyman, and even drones).
click here to download the app (for users in the US for now) and get all the help you need.
Good luck!

Posted on Jan 02, 2017

Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

Is there a battery in the t8000c thermostat the screen is blank

There should be a couple of AAA batts in it. Grab all 4 corners and pull straight out & off the mounting plate. If no batteries are installed it is hard wired & the problem is at the air handler(blown blade fuse or open transformer winding). When you reinstall batteries make sure there is no corrosion. And careful when you put the tstat back onto the base. There are some small pins that need to align with its holes/terminals. Honeywell has a great 1-800 support #. Should be on the tstat.

Jun 28, 2015 | Honeywell TH8320U1008 VisionPRO 8000...

2 Answers

Honeywell t8000c display is blank, unit doesnt run

I would say that you have one of two issues. Either your thermostat is bad or you do not have 24v coming from the heating unit. In this case the problem would be in the low voltage circuit of the heater. At the heater you should have 24v AC when you place an electric meter across the R terminal and the C or W terminal. If you have no vaoltage across the R to either the C or W then you have a bad transformer or a blown fuse in the furnace. If you do have voltage ther and also at the t-stat then the t-stat has gone bad, replace it.

Nov 14, 2009 | Honeywell Electronic Programmable...

2 Answers

Honeywell T8011r does not have anything on display - does not appear circuit breaker is thrown - could it be wire disconnected at the plate or is there a fuse inside the unit?

Check to see if you have power at the furnace. You thermostat is powered by 24vac coming from the furnace. You should have power on the "R" terminal.

Oct 05, 2009 | Honeywell Electronic Programmable...

2 Answers

A/C not turning on - Digital screen is blank

Your honeywell should have battery back up but the primary power for this is a 24 volt transformer located in the air handler probably in your attic. All these controls run on 24 volts

Jul 11, 2009 | Honeywell Programmable Thermostat Heater

2 Answers

T8000c honeywell thermostat is blank

This unit doesn't require a battery. It runs off the 24v from the unit. Check that your transformer is still working. Check the control board for 24v pwr. and main pwr. Check your breaker to the unit. It could be as simple as a bad stat too. You can check by using a jumper wire and jumping across from r term. to y term.

Apr 10, 2009 | LG Art Cool LA121CNP wall/window Air...

1 Answer

Central honeywell air conditioner

Sounds like it may have lost power. Check the breaker and the fuse at the furnace. If they are all in the on position and working then it sounds like you may need a technician. If the display is blank on the thermostat you may also want to replace the batteries.

Jun 12, 2008 | Honeywell Electronic Programmable...

Not finding what you are looking for?
Heating & Cooling Logo

Related Topics:

8,015 people viewed this question

Ask a Question

Usually answered in minutes!

Top Heating & Cooling Experts

Paul Carew

Level 3 Expert

3173 Answers

Dan Webster
Dan Webster

Level 3 Expert

8220 Answers

Tim Whalen

Level 3 Expert

3074 Answers

Are you a Heating and Cooling Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides