What happened

moleman

When we got back home after three days away, upon entering the house we noticed it was cold. Checked the thermostat and the desired temp was set to 67 but the house was 53 degrees and the stage 2 setting was on. Felt the air at the registers and it was not cold but very tepid. Let it run a while but no change. My wife did not want to have the blower keep running so I turn the thermostat to its lowest setting. Before giving up and calling someone out on a Sunday we just put on the fireplace which heats the house well and decided we’d call on Monday. But I decided to give it one more try. I went and turned the system off at the breaker and back on. I set the thermostat at 67. It was still in stage 2 and not heating well. I waited until the house temp got back up from the fireplace within four or so degrees of 67 and set the thermostat at 67. Once it was within two degrees of 67 it changed back to stage one and held the house warm overnight and continued to do so.
The tech from our heating company called us and I explained the details. He said it possibly was in defrost mode. For 3days? And the coldest overnight temp was 35 degrees? He said call if it happens again. Any ideas what happened? Thanks

ethicalpaul

I know nothing, but it sounds like your stage 2 is busted. As long as you keep it only needing stage 1 it might be OK. But maybe while you were away there was a setback or a cold snap and once stage two was needed, it no longer heated sufficiently

HVACNUT

What is Stage 2? Is it a 2 stage heat pump (Y2), or auxiliary electric resistance heat, or something else?

Jamie Hall

Kind of agree with the above — except that we have no idea what kind of heating system this is, except that it blows air out of registers…

It does sound very much as though it is a two stage system — with a two stage thermostat. To get some sort of general concept of these, most of them will operate on stage 1, so long as the heating demand isn't too great. However, if the heating demand increases, they will bring on stage 2, which may — or may not — leave stage 1 (whatever it is) operating. Often not.

So @ethicalpaul 's diagnosis makes a great deal of sense. The heating demand increased for one reason or another, and the system tried to switch to stage 2 — but stage 2 wasn't working, and so long as the heating demand stayed that great, you got no heat at all to speak of.

Now this could be either the heating system — or it could be a faulty thermostat which says it is calling for stage 2 and even thinks it is — but the message isn't getting to the heating system.

Some interesting troubleshooting going to happen here!

EBEBRATT-Ed

Since the tech mentioned defrost, we can only assume heat pump.

It's probably a defective defrost board and it is stuck in defrost with the electric heat working somewhat. Could be a defective termination sensor