I have a Thermopride, 2 stage NATURAL GAS fired
Condensing Furnace
Model # CHX1-75N
Almost 5 years old
95% Efficiency
Lux products programmable thermostat- Series 602

The issue that we are having is when the furnace has not had enough time to rest in between cycles. It will bring it up to the proper temperature but if is COLD out and it needs to run soon after it shuts down it will start, stop, start, stop start, stop without ever increasing the temp in house. It will go from 62 degrees to 70 without a problem when the thermostat calls for it and run until it raises the 8 degrees needed such as when we are on our way home from work.

If the house temperature is up to what the thermostat calls for and it needs to start relatively soon after it will act up every time. We do not really have a time frame on this but if it needs to kick the heat back on in less than 6-8 minutes it simply will not cooperate. It has not really been too much of an issue to us but at the present time it is still under warranty. (ONLY THE PARTS NOT LABOR)

We live in Ohio and we had temps 2 consecutive mornings that were -8 and -15 and needless to say the furnace does not stay off for long when it is that cold outside. When the temperature is mild 20 degrees and above it works fine. I will call a serviceman more than likely but when you have an intermittent problem you have to get them here when it malfunctions.

Any ideas on what the problem could be? THANKS in advance for your help.

I actually love the furnace as it has cut our gas bills more than half. I haven't even had one over a hundred dollars so far this year and everything in the house is GAS (furnace, water heater, clothes dryer and range)

Sounds like possible thermostat problem. Was the thermostat replaced with furnace? If not, can you tell me what type of thermostat you have. There may be a setting on the thermostat that need adjusting. Please let me know.

Could also be a flame senser problem. Does your furnace have diagnostic lights? If so let us know what they are doing.

We also thought it could possibly be the thermostat so we bought a new one and installed it and it still acted the same way. The thermostat is a Lux Products series 602 multi-stage digital programmable (5+1+1) made in Laurel, NJ. It is not a cheap thermostat and neither was the one that we purchased to replace the old one. They were about $85.00 each. Since the thermostat did not solve the problem we reinstalled the original. The old thermostat (copper colored round Honeywell that everyone's had) was replaced with this digital Lux Products thermostat when the furnace was installed as we also installed a 2.5 TON 14 SEER central air unit at the same time.

The thermostat that was reinstalled , the furnace and the central air unit will be exactly 5 years old this July. All of these units were brand new when installed.

Yes the furnace does have the diagnostic lights the RED one flashes 2 times and as far as we can tell the GREEN one flashes 9 or 10 times.

Just want to say "THANK YOU" mygirlsdad77 for the reply it is very much appreciated.

One more little note- it is mild in Ohio today (mid 50's) we had to make it act up today to read the codes by making it run until it got to 71 degrees, then when it shut down I waited less than two minutes and raised it to 74 degrees and this is when it could not nor would not run to get to the set temperature on the thermostat. After it failed twice I lowered the thermostat back to 70.
If it gets to either cool off or rest it seems like it will run like it should. The problem occurs when it has to cycle too often. Just to let you know I already set the thermostat to have a 2 degree swing hoping to keep it running when we are not home to babysit the furnace. This is the Max the swing can be set at.

The problem was really frustrating when it was cold here (single digits and below) because the house is 100 years old and the furnace had to cycle way too often. The house does have insulation but it is by no means tight like new homes.

OK, the flashing lights. There should be a place on the inside of the furnace door that will tell you what the flashing lights are saying. Please let me know what the diagnostics read. Intermittent problems are a hvacr techs worst nightmare. But if you can get that code down, we may be able to help. Good luck and I hope I can be of further assistance.

According to my Thermopride installation and operation manual the
2 RED FLASHING lights mean low pressure switch stuck closed and
The 9 or 10 GREEN FLASHING mean an estimate of the air flowrate(in CFM) produced by the house air blower ---1 flash per 100 (programmed) CFM.

SORRY I did not include this in my last post. THANKS!!

I think I would start by replacing the low pressure switch. They are fairly inexpensive(depends on what you call inexpensive). Its hard for me to say without being there to actually test components, but judging from the info above, I would start there. Please let me know how things work out.

Will post update when we get this repaired. THANK YOU SO MUCH FOR YOUR HELP!!

Looking forward to it. Thanks.

THANK YOU "mygirlsdad77"you were right on the mark.
We did not call a repairman as we decided that we would first try cleaning the flame sensor as you had suggested. I have to say when my husband pulled it out he thought that it wouldn't help to clean it as it didn't really look that bad and I had to agree, but I told him since he had it out to give it to me and I cleaned and shined it with a piece of emery cloth and reinstalled. Truly thought it must be a fluke as furnace ran fine for a few days but then I purposely made it run back to back 3 times in a row with only 2 minutes in between and EVERY time it worked. It certainly wouldn't do this before. I now have a furnace that works!! :) Last month was really cold, we had several days down to zero and one was -15 and one -8. Just to let you know my gas bill was $120 (pleasantly surprised) it would have probably cost close to that for the repairman. THANKS A MILLION, You're the best!! :):):)

Glad you got it fixed yourselves. Good job. Dirty flame senser is very common, something to keep in mind for the future.

Absolutely will remember this for future reference. Thanks so VERY VERY much. I've been laid off for almost a year and really didn't want to spend the money on a service call if I didn't have to. Thanks to you I didn't. I have no idea what people did without the internet and help forums, truly a blessing. THANKS AGAIN!! :D