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My thermostat T8400c 1024 Won't turn on the screen is just blank

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3 Suggested Answers

koolbreezes
  • 540 Answers

SOURCE: digital thermostat not working

Can you saY, Batteries!

Posted on Sep 15, 2008


mpcheeseman1
  • 1400 Answers

SOURCE: I have a Honeywell T8400C

Hello
Try taking the batteries out for 5 min,or disconnect power for 5min.
To clear it out.
Then re input all your times days and temps,

Is t stat in a cold location near a door or window?this could also override your settings,most progrmamble stats will go into override at 58.f im guessing this is not your problem.

If it continues after you reset,i would consider a new thermostat.

Hope this helps.

Posted on Jan 28, 2010

heatman101
  • 43501 Answers

SOURCE: changed honeywell T8400C 1024 to

Hi,
On the t-stat and the furnace make sure the wires are hooked like this...

Red to R
White to W
Green to G
Yellow to Y
Blue to C

then it should work..

Thermostat Wiring and Terminal Designations

heatman101

Posted on Jun 12, 2011

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1 Answer

The display on my thermostat T8400C 1024 isn't working. Everything else works but the heat and the flame is not igniting either. Please help.


Sounds like a manual limit needs to be reset (thermal disc). Generally the manual limits are around the exhaust - backdraft, or burner assembly - flame rollout.

Feb 15, 2014 | Honeywell Heating & Cooling

1 Answer

I HAVE A HONEYWELL MANUAL THERMOSTAT NO BATTERIES ALL IT HAS ON THE BACK IS T8400C 1099 (2) 0710 1B HELP, IT DOES NOT SHOW ANY THING THE SCREEN IS BLANK


This model of Honeywell thermostat uses the 24v from the unit to power it. One of three things must have happened.

1. You have lost power to the furnace, therefore no power to thermostat.
2. You only have 4 wires hooked up on the thermostat and not 5. A lot of older homes had just 4 wire running to the thermostat, which will not work for this thermostat. You should have a wire connected to the (C) or (B) terminal on the thermostat, which ever one they have, I can't remember off hand. These are the Common terminals. They have to have the common from the furnace 24v power to operate.
3. Faulty thermostat, which will obviously have to be replaced.

Hope this helps and gets you to cooler days!

Jun 28, 2012 | Honeywell Heating & Cooling

1 Answer

Changed honeywell T8400C 1024 to Hunter 44760, I have five wires white, red, yelliow, green, blue. Hunter Thermostat reads "NO A/C Power.


Hi,
On the t-stat and the furnace make sure the wires are hooked like this...

Red to R
White to W
Green to G
Yellow to Y
Blue to C

then it should work..

Thermostat Wiring and Terminal Designations

heatman101

Jun 12, 2011 | Heating & Cooling

1 Answer

My honeywell t8400c also went blank. I can not find a battery anywhere and if plugs into the wall to get electricity. Everything works but the digital read out. Any suggestions


it should take a battery and it has wires coming from the unit for power as well the stat splits open from the wall leaving some of it mounted on the wall the batteries are in the part that pulls off the wall and the wires are on the part that stays on the wall the power wire is red on r terminal

Sep 23, 2010 | Honeywell Electronic Programmable...

1 Answer

I have a Honeywell T8400C 1024 thermostat. the last two nights, our heat continues to run without shutting off at the pre-set temperature. We have woken up to 81 degrees in our house. What is the...


Hello
Try taking the batteries out for 5 min,or disconnect power for 5min.
To clear it out.
Then re input all your times days and temps,

Is t stat in a cold location near a door or window?this could also override your settings,most progrmamble stats will go into override at 58.f im guessing this is not your problem.

If it continues after you reset,i would consider a new thermostat.

Hope this helps.

Jan 28, 2010 | Heating & Cooling

1 Answer

Honeywell T8400c thermostat went blank. central heating is not working although warm water is alright. any idea?


I would check the batteries in the thermostat. If the batteries are okay then you might have a blown fuse in the furnace or the furnace lost power check the breaker.

Jan 21, 2010 | Heating & Cooling

1 Answer

Honeywell thermostat t8400c intermittent blank screen


It actually sounds like the batteries are going dead if the 24v from the furnace are not providing the power to the thermostat.

Sep 28, 2009 | Honeywell Electronic Programmable...

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