Hi. I apologize in advance for the long post. I have a 10 year old York gas furnace (Model P1CK; Upflow; 32-112 MBH Output) that's been functioning in a peculiar way. The outside temp in this area has been about 65-70 daytime high and 35-45 at night. I have the thermostat set for 66 degrees with Auto selected. Every day between 11:30 am and 1:00 pm the heat will come on. It will operate normally and maintain the set temperature for about 3-5 hours. After this time it will no longer respond to the thermostats call for heat until about the same time the next day. This is making for some cool evenings and mornings.

I have had technicians from two different companies come to inspect the unit (under a homeowners warranty). On the first inspection the LED indicator was flashing and the tech replaced the circuit board and flame sensor. The unit worked fine for about a day and a half and then returned to its original pattern of operation. Since then the LED has not indicated any problems even when the furnace is not responding.

The next tech replaced the old thermostat with a Honeywell (non-programmable) and cut the wires leading to the furnace to make fresh connections. He also rewired the thermostat and furnace to use a different wire in case the original (white) wire was bad. This time the furnace maintained the temp for a few hours and then quit until the next day. At this point the tech called our homeowners warranty company and requested a York specialist. We're still waiting for one to show.

After reading the FAQ's for this forum I am suspecting that the thermostat is calling for the furnace to turn on, the 24 V signal is going to the furnace (tech confirmed) and then either the pressure valve or some other safety switch is not allowing the initial blower to activate since I never hear it turn on. Does this sound reasonable? And should this trigger the LED to indicate a problem?

If this doesn't sound like a plausible scenario, does anyone have any suggestions as to what might cause the furnace to not respond, yet show no indication on the LED?

Also, I have no clue as to why the furnace operates in such a cyclic manner. It could just be a coincidence. We don't have any kind of temperature control system other than the thermostat. I have even called my gas company to find out if there has been any interruption in our service of if there could be a problem with the gas line. They said it was highly unlikely.

Well, if anyone can offer an opinion I would appreciate it. I know next to nothing about home heating (although I'm learning fast) so, if I left out any key information or overlooked the obvious please forgive me.

Thanks,

CJV

I was all set to blame the thermostat until I finished reading your post. With a new stat and 24v reaching the furnace this isn't going to be your problem. I think you are stuck waiting for the tech. I never advise people to work on appliances that are under warranty, why should you and you could void the warranty. If 2 techs in your home have not found the problem you should be making more noise with the repair supervisor. By the way, is this a manufacturers warranty on the furnace or a home owner warranty you got when you bought the house?

This is a home owner warranty we got when we bought the house. I've been bugging them quite a bit. Apparently, finding a York residential heating specialist is tough in these parts. We've had the house about 3.5 weeks. The furnace worked fine for about a week and a half I guess, then it got crazy.

You could freeze to death waiting for the York tech. There are some simple checks you can do while waiting without causing any problems. The next time the furnace won't run, I would look to see if the indicator light is on. It should always on when the furnace has power unless it is flashing a code. If it is not on, check for power to the furnace, and check to see if you have 24 volts at the R and com terminals at the furnace. There is a safety switch you have to hold in to check power with the cover off. If you have some sort of an intermittent power loss, either the 120 or the 24 volts, it won't set codes and the techs won't find the problem if it is not when they are there.

If the light is on, try putting the fan in the On position. If it doesn't come on, it could be a problem with the connections between the thermostat and the furnace. If it does come on, try turning the power to the furnace off, and back on. If the furnace then starts up, you may have a problem with the fan controls. I can't say why a code for it isn't showing up.

A long question is much easier to answer than one missing important information.

Please post back. If the above doesn't help, maybe one of the better people here will show up. I did what I could for a long time, but was very happy when Northern Heat joined. Now there are some others giving good answers too.

Since it's a home owner policy you aren't getting top of the line repair people. Many aren't much more than handymen so keep making noise. I'd also make some calls to the real estate broker if you used one in the purchase.

First off, thanks to both of you for responding. I truly do appreciate it.

As for the indicator light, I have not seen it on at all since the first tech replaced the circuit board on Monday (3/5). I just looked through the view hole (since the furnace has been functioning since 12:30 today) and it was not on while the furnace was running. I suppose its possible that the indicator light has burned out?

If I can find my voltmeter (still not unpacked yet), I will check the 24 volts at the R and com terminals later tonight when I know the unit is not responding. I'll try and do the safety switch check also. I'll have to check back at the FAQ to get an idea of where that actually is.

If it turns out that the furnace is not receiving 24 volts am I correct in assuming that its because of the thermostat (or that set of wires, at least)?

If its not receiving 120 would that be the wires coming from the circuit breaker box or a fault in the breaker itself? Its weird that it would cut on and off like this, but stranger things have happened I suppose.

A specialist tech is scheduled to come by tomorrow so hopefully this can get resolved. Thanks again for the suggestions. I'll definitely post back to let you know what I find and how things go tomorrow.

CJV

Most of those lights are LED's that don't burn out and are usually soldered in. If the light isn't on when the furnace is running, the new, big buck circuit board is bad. The 24 volts comes from a small transformer usually near the control board powered off the feed from the house. It supplies both the 24 volt control voltage and power to the board logic. The red wire supplies 24 volts to the thermostat.

There are several ways for the 120 volt supply to fail, mostly a bad connection somewhere. It deosn't sound like the problem in this case. The safety switch is where the cover hits it as you slide it completely closed. It is often right where the power feed comes in.

I don't think you will get much relief until the York guy replaces the board. Sometimes a fulty board will respond to cutting the power off and back on.