Honeywell CT2700 Thermostat

[Angle Iron]

Older digital programable thermostat Honeywell CT2700A1019(1) a friend has is showing F5 on the display and is not working. Any idea as to the cause. Unit was shut off prior to a storm that blew through a couple weeks ago. Lost power for a day. Went to turn on the AC yesterday and now he says it shows F5 on the display. Also said when set to fan on the fan would run a few seconds and stop. That seems to have resolved it self but still the F5 shows and will not run in ac.

 

[Stan Coryell]

The code doesn't show up. If the Fan works, I'd guess it's time for a new stat. Is the battery good? I don't think the stat has common on it>

 

[Angle Iron]

I had the code wrong it is 5F if that matters. I either transposed it or he told me wrong. Thanks for now.

This post was edited by Angle Iron on 10/13/2022 at 09:48 am.

 

[Steve@Advance]

I pulled up the owners manual, it didn't show any codes.

I wonder if it's had a brain malfunction, or lost segments of the display.

Did you try taking the battery out and letting it reset?

Could also try removing the wires, connect red to green, see if the fan comes on. Red to white should bring
heat. Red to yellow for cool. Red to orange for heat pump.

If all that works, replace the thermostat. Be sure to match the stat and settings to the system.

 

[Geo-TH,In]

I had a new center AC installed last year
In a hot Sunday the thermostat was damaged
by shorted 24vac coil on the compressor
contactor.
Bought a new thermostat. It hot damaged
too.
I rewired my central with a used 40 year
old mercury homeywell thermostat.
Replace contactor with a used one.

Friend in HVAC business says he replaces a
lot of digital thermostats, $50 his cost.
He carries new ones in his truck.

You can still buy the old style round
Honeywell's. Need to add a 5 minute
compression delay. about $20

I'll never get a fancy digital thermostat
after the pain I went through and friend
says he makes many service calls because
of the digitals.

 

[Angle Iron]

At this point I am taking his word on most of this. He says it has no battery, having said that I am not sure. He said it could be as much as 20 yrs old, put in around 2000 or so. Again I am repeating what he has said. I may get a chance to look at it soon. Thanks for the answer.

 

[wore out]

Looks like some versions MAY have a coin-cell battery on the circuit board, pull the 'stat off off it's was bracket and have a close look.

IF you find a battery, remove it and let the electronics reset, replace with a new battery.

If no battery, likely it uses a capacitor to store power to keep it operating while it is operating the furnace.

If NO battery, leave it unplugged form the base for a few minutes to completely power down before plugging it back into the mounting base, POSSIBLY resetting it.

 

[Geo-TH,In]

I don't recall the name of my digital I replaced with an old school honeywell.
My digital had a common 24vc and didn't need a battery.
Some HVAC service tech don't wire the common and use 2 1.5 v AA instead.
They think a power surge can damage the thermostat.

 

[Angle Iron]

In the end it seems it was just a bad thermostat. New thermostat and all is well, thanks to all who answered. Unless it had some sort of internal built in battery we couldn't find one. It was just a 4 wire set up. Thanks again.

 

[Geo-TH,In]

My friend that repairs HVAC says he replaces a lot of new
digital thermostats.

45 years ago I bought a house with the old school mercury bulb
honeywell.
I'll never replace it with a new style thermostat.

I replaced my digital thermostat in my other house with a used
old round honeywell. Works fine.

Sounds like the new digital thermostats gives the lonely AC
repairman something to do..

 

[Angle Iron]

(quoted from post at 03:10:01 10/14/22) My friend that repairs HVAC says he replaces a lot of new
digital thermostats.

45 years ago I bought a house with the old school mercury bulb
honeywell.
I'll never replace it with a new style thermostat.

I replaced my digital thermostat in my other house with a used
old round honeywell. Works fine.

Sounds like the new digital thermostats gives the lonely AC
repairman something to do..

This one was put in around 2000 and had been flawless until it wasn't. I have had two here at the house, one from 87 to 2002 and the other is still working 20 yrs later. They do fail like anything else electronic. The newer the unit the better the low voltage circuit protection. Yet they still fail just harder to figure out what is wrong. You could see what was going on on the old mercury or point stats but in many cases were not as accurate. I did some repairs 30-40 yrs ago, a lot has changed in that time and I am lost in most of it now. Thanks again.