I have a Honeywell TH800 Series thermostat controlling a heat-pump and furnace for forced air and aux heat.

Last week the touchscreen stopped responding. After playing around with it I took it off its mount and discovered a) it took batteries, and b) the batteries had been in too long and leaked. I cleaned off the worst of the crud and tried new batteries but still no touch screen.

I found other people suggesting the ribbon cable might need to be reset (eg https://homeheatproblems.com/honeywell-8000-pro-touch-screen-stuck-or-frozen/). When I cracked it open I found the battery crud had also reached and corroded a corner of the circuit-board. I tried cleaning that area as best as I could with rubbing alcohol (and had to resolder one of the battery terminals when it popped off for my trouble). The touchscreen came back for an hour and then died again. I've tried a bit more cleaning and resetting the cable but right now it's running the last program I set and not responding to input.

Obviously, with the board corroded I should replace it before I need a different program or it dies.

Knowing that SE sites don't permit product recommendations my question is, if I want to do a drop in replacement, is there anything I should be cautious of. Any features I might considering upgrading for in terms of quality life? Anything I should looking for in product information that might interfere with a drop in replacement. And anything else I should be cautious of doing this replacement.

Ideally I just want to unscrew the existing mount and terminal block, wire up the new one identically (with the same jumpers I see?) and go. I am not planning any changes to the HVAC system except replacement if components die. If anything location specific enters into this, I am in British Columbia, Canada. thermostata terminal block terminal block left terminal block right heat pump heat pump nameplate furnace Additional image of the wiring in the furnace furnace wires close up wires

  • Can you post photos of where the thermostat wiring connects to your furnace please? Jun 5, 2021 at 23:32
  • @ThreePhaseEel added additional images
    – Phyzz
    Jun 6, 2021 at 6:07

1 Answer 1


Any modern thermostat will do the job but you'll need to understand how to adapt all those wires to different ones.

You have wires connected to the S1 and S2 terminals. Those should go to outside thermometers. If you actually have outside thermometers you should get a thermostat that uses those signals. You'll have to look at the spec and docs but there are new Honeywells that do that.

Some Smart thermostats make use of web wether services to do the same thing. If you get one, you can just disconnect the S1 and S2 wires (assuming, again, that they are even connected to anything).

Everything else is standard for any heat-pump compatible thermostat.

You appear to have a C wire there. Assuming it is actually connected at the other end to a 24V C connection, you should buy one without a battery.

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