Sometimes when I have the furnace set on automatic it will not turn on when the temperature goes below the set point. All I have to do in order for it to work again is turn the furnace off then back on (I do this at the thermostat) and it will work fine for a day or two, then the same thing happens again. Is it the Thermostat?

Any and all help would be appreciated!!

Brand of furnace?
Exact model number of furnace?
Brand of thermostat?
Exact model number on thermostat?

Sorry it has taken me a while to respond. The reason for this is because right after I posted the question the problem stopped. But the problem has started up again. Here are the answers to you questions:

Brand of furnace- Ruud Deluxe 90 Plus
Exact model number of furnace- UGED-06EMAES
Brand of thermostat- Honeywell
Exact model number on thermostat- T87F 23943 (I believe this is the model # as it was one of two #'s on the thermostat)

It seems that problem only occurs when it is realativley cold outside (below freezing).

Thanks for your time,
Danny

Does the circuit board on the furnace have a diagnostic LED? If so, check it the next time you experience this problem. Usually, a label describing the fault code translation can be found on the access panels of units equipped with self-diagnostics.

Thanks for the reply. I checked and do not believe the unit has a diagnostic LED. The unit is older maybe 10-15 years if that helps. You should also know that the thermostat is a non-electronic mercury dial thermostat.

Danny

If the action of switching the thermostat off/on causes the system to work again, the selector switch may be worn/oxidized. Mercury, eh? Sounds like it's time for a new one anyway. Even if it doesn't solve the problem, it's still a good investment and riddance of a hazard.

I am not 100% sure it is mercury but it sure looks like it. Can you give me an indication of where the selector switch is located?

Thanks again for your help.

On the thermostat (heat/off/cool).

I would start by replacing the thermostat, it may not solve the problem, but if will eliminate the thermostat as the problem. If you have an older Honeywell t87f thermostat, then is is most likely mercury. The coiled spring has most likely worn out, causing problems with accuracey. Try turning the thermostat all the way up next time the furnace fails, if it comes on, then you have a bad thermostat. If it doesn't, the problem is most likely somewhere else, but I would replace therm anyway. Please let us know how things work out.

Quote:

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Originally Posted by KC13

If the action of switching the thermostat off/on causes the system to work again, the selector switch may be worn/oxidized. Mercury, eh? Sounds like it's time for a new one anyway. Even if it doesn't solve the problem, it's still a good investment and riddance of a hazard.

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Okay I changed the theromstat to an electronic one and checked the contections twice. But unfortunately the same problem exists. The furnace will come on then shut off before the desired tempurature is reached. If I manually turn off thermostat to the "off" position then back to the "on" position the furnace starts back up again, but still shuts off before the desired tempurature is reached.

Any help would be apprciated.

Danny

The new t-stat is still a good investment, sorry it didn't correct the problem. Switching the system off/on is cancelling a timed lockout imposed by the circuit board control. Since you have a condensing furnace and the problem seems more prevalent in colder weather, I would suggest checking the drain tubes and trap for blockage. Remove and flush thoroughly with water. Check the intake (if present) and exhaust pipes for blockage or horizontal sags which may be trapping water.

Try cleaning the flame senser. Simple to do and doesn't cost you a thing. The flame senser will have one wire going to it, it will have one screw that holds it in place. It will be on the opposite side of the burner from the ingniter. Just remove it, clean it with an abbrasive cloth(sandpaper, sandcloth, steelwool, etc). Don't confuse it with the igniter. The flame senser will be a single probe. Please clean it and let us know if the furnace works. If it doesn't work after doing this, then we will take the next step.

Quote:

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Originally Posted by mygirlsdad77

try cleaning the flame senser. Simple to do and doesnt cost you a thing. The flame senser will have one wire going to it, it will have one screw that holds it in place. It will be on the opposite side of the burner from the ingniter. Just remove it, clean it with an abbrasive cloth(sandpaper, sandcloth, steelwool, etc). Dont confuse it with the igniter. the flame senser will be a single probe. Please clean it and let us know if the furnace works. If it doesnt work after doing this, then we will take the next step.

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I have search the internet for pictures of where the flame señor might be on the furnace but I have not had any luck. I also looked at my furnace with no luck. I tried to upload a picture of my furnace with no luck. Thanks for your help.

Danny

Stay tuned, hvac1000 will eventually see this, post a pic of some flame sensors for you, and pad his retirement fund once again.:D

Sorry Danny, I won't give out my email. Nothing personall, I just can't bring myself to do it. I suggest not giving yours out publicly either. If you want to give it out, maybe try sending it in a personal message.

I really do want to help you. If you could just give the make and model of your furnace, I should be able to look it up and locate flame senser. Good luck.

Quote:

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Originally Posted by mygirlsdad77

Sorry Danny, i wont give out my email. Nothing personall, i just can't bring myself to do it. I suggest not giving yours out publicly either. If you want to give it out, maybe try sending it in a personal message.

I really do want to help you. If you could just give the make and model of your furnace, i should be able to look it up and locate flame senser. Good luck.

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No worries I completely understand. I really to appreciate your help. Here is the info you requested.

Brand of furnace- Ruud Deluxe 90 Plus
Exact model number of furnace- UGED-06EMAES

Quote:

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Originally Posted by mygirlsdad77

Sorry Danny, i wont give out my email.

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I'll sell it to you... or accept hush money from MGD not to... :D

OK Danny lets try a cheap and quick test. Disconnect the R and W wires at the terminals at the furnace. Then jump the R and W terminals with a piece of wire or jumper cord. Turn the furnace back on and let it run. It should continue to run non stop. The temperature will continue to rise in the home but no harm will be done. Stay by the furnace and watch it operate and note any deviation from the constant burner running. After 10-15 minutes of this turn the unit off and report back with exactly what happened.

Here is the flame sensor as requested$$$$$

Quote:

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Originally Posted by hvac1000

OK Danny lets try a cheap and quick test. Disconnect the R and W wires at the terminals at the furnace. Then jump the R and W terminals with a piece of wire or jumper cord. Turn the furnace back on and let it run. It should continue to run non stop. The temperature will continue to rise in the home but no harm will be done. Stay by the furnace and watch it operate and note any deviation from the constant burner running. After 10-15 minutes of this turn the unit off and report back with exactly what happened.

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I will do it right now. I will get back to you in a few. I feel like I am in the middle of an inside joke with the flame sensor picture (mentioned by KC13) and $$$$$.

Thanks for your help.