Thermostat or furnace problem?

Go and replace the thermostst anyway. Its a very cheap and easy way to find if that is the problem. You end up with a new controller in any event.

I suggest the thermostate controling the furnance may not be in the same location (or may not be calabrated the same) as the one you are looking at. (see below about one wire)

I also could be an anticapater set far too high.

With the two problems, (wire and temperature control) not appearing to be connected, I suggest you call in the professional and they should be able to fix you up quickly.

Something is not right. A thermostate can't work with just one wire. My guess is you are not looking at what you think you are looking at.

Then you are NOT looking at the thermostat that is controlling the furnace...

Period.

Maybe the anticipator in the thermostat is screwed up. So the thermostat thinks the room is approaching the right temp and cuts off early to avoid overshoot.

Another possibility is the contacts in the zone valve are shot and can't start the burner&circulator.

Could be....but... The thermostat he is claiming to look at, has ONE wire hooked up...and every single one ever, needs at LEAST 2. A thermostat is nothing but a switch. Power in, power out. One wire, with a cut wire hangin back...wont work, not at all.

Sounds like your furnace guy is going to earn his keep today. That doesn't sound right, 90 minutes to get up to temp..... and it's even colder?

Thanks again for all your help. To recap the problem: it sometimes would take 6 hours for house to heat up 6 degrees, and occasionally the house would be colder than the lowest programmed thermostat setting. The problem was compounded because it was intermittent-- sometimes no problems, sometimes problems.

As a first fix, I replaced the batteries in my thermostat. Turns out they were low on juice, but not so low that the "lo batt" indicator came on. The first two days after I changed the batteries I had no problems. Then (on a weekend, of course), the house took 6 hours to heat up, with the furnace blower staying on for at most a minute or so at a time.

The repair guy came on Monday. I have a Trane furnace, about 12 years old, everything original. Repairman turns the thermostat from 70 to 75 degrees. Of course, the furnace works like a charm, heating up the house a degree every 10 minutes or so. Furnace guy says it's the dreaded intermittent problem, which is hard to diagnose. He suggests 4 possible causes:

He suggested that he try to fix (1) and (2), since they were likely culprits and not too expensive to fix (unlike the control panel). Fortunately, the furnace shut down when the house was only at 74 degrees, and he said it seemed like some kind of pressure problem (over my head-- I had no idea how complex the furnace was). Anyway, he cleaned the sensor and flushed the pump, and everything has been working well the past few days. Here's hoping that was all it was.

Thanks again, all! If I have any more problems, I'll post.

Doug