[brubble01]

I have a Ruud high efficiency furnace that's giving me fits. The problems started a few weeks ago when I woke up to a cold house. I reset the breaker, it wasn't tripped and the unit seemed to work as it should for a few days, then it happened again. I checked and reseated all the electrical connectors, and reset the breaker again and it worked fine for a few more days. I had an old mercury type themostate so I replaced it wirh a simple electronic unit, reset the breaker and it worked for a week or so with no problems, then malfunctioned again. I checked all the electrical components as best I could with my fluke and everything seemed to be as it should, reset the breaker and again it worked fine for a few days. I puchased and replaced the two wire limit switch, even though it seemed to check out okay and again it worked fine for a few days. The unit acts the same whether I have the rollout switch in line or not so I assume it is okay and checks okay with my meter. I'm beginning to think I must have an intermittent control board problem or some sort of timer or relay problem, as it works great until it just intermittently shuts down and the temperature drops to uncomfortable levels. Now it doesn't seem to want to work correctly even after resetting the breaker.
Reset the breaker to restart the unit, the inducer motor starts, then the fan starts, after a few minutes the ingniter glows and the burner lights. It burns for a about thirty to forty seconds and then stops, which I assume is some sort of preheating. A minute or so later the igniter glows and the burner lights again and burns for a couple of minutes, beginning to warm the house a little. A few minutes later the igniter lights the burner and buurns for several minutes and will eventually bring the house to the proper temp, the thermostat no longer calls for heat and it seems to be okay. The inducer motor seems to run continuously until the proper temp is reached and the thermostat no longer calls for heat, but the blower motor cycles on and off. I replaced the start capacitor last summer when the blower didn't seem to come up to the correct speed during the AC season, it seems to reach the right speed but does cycle on and off even though the thermostat calls for heat.
This has become a perplexing situation for me because I never know if I'm going to wake up to a cold house or come home to one after work. It may work fine for days and then the problem rearises, any ideas. I'm in the office machine business and have repaired everything from mechanical typewriters and calculators to electronic cash registers, copiers and laser printers but the furnace has me questioning myself.

[brubble01]

I have a Ruud high efficiency furnace that's giving me fits. The problems started a few weeks ago when I woke up to a cold house. I reset the breaker, it wasn't tripped and the unit seemed to work as it should for a few days, then it happened again. I checked and reseated all the electrical connectors, and reset the breaker again and it worked fine for a few more days. I had an old mercury type themostate so I replaced it wirh a simple electronic unit, reset the breaker and it worked for a week or so with no problems, then malfunctioned again. I checked all the electrical components as best I could with my fluke and everything seemed to be as it should, reset the breaker and again it worked fine for a few days. I puchased and replaced the two wire limit switch, even though it seemed to check out okay and again it worked fine for a few days. The unit acts the same whether or not I have the rollout switch in line or not so I assume it is okay and checks okay with my meter. I'm beginning to think I must have an intermittent control board problem or some sort of timer or relay problem, as it works great until it just intermittently shuts down and the temperature drops to uncomfortable levels. Now it doesn't seem to want to work correctly even after resetting the breaker.
Reset the breaker to restart the unit, the inducer motor starts, then the fan starts, after a few minutes the ingniter glows and the burner lights. It burns for a bout thirty to forty seconds and then stops, which I assume is some sort of preheating. A minute or so later the igniter glows and the burner lights again and burns for a couple of minutes, beginning to warm the house a little. A few minutes later the igniter lights the burner and buurns for several minutes and will eventually bring the house to the proper temp, the thermostat no longer calls for heat and it seems to be okay. The inducer motor seems to run continously until the proper temp is reached and the thermostat no longer calls for heat, but the blower motor cycles on and off. I replaced the start capacitor last summer when the blower didn't seem to come up to the correct speed during the AC season, it seems to reach the right speed but does cycle on and off even though the thermostat calls for heat.
This has become a perplexing situation for me because I never know if I'm going to wake up to a cold house or come home to one after work. It may work fine for days and then the problem rearises, any ideas. I'm in the office machine business and have repaired everything from mechanical typewriters and calculators to electronic cash registers, copiers and laser printers but the furnace has me questioning myself.

Problem undate, there seems to be a problem with the pressure switch. The inducer blower either does not create enough vaccuum to always activate the switch or the diaphram in the switch is bad. The switch activates as it should if I give very little suction on the tube, but the inducer does not seem to give sufficient vaccuum suction. How much should be needed? Is it more likely to be the switch itself or the induction motor, which seems to run strong but produces little vaccuum? Is there some sort of gasket internal to the blower assembly that has deteriorated.

[letmetellu]

You said that you kept resetting the breaker... but you said it was not tripped but it still made the furnace work??

The problem you describe is associated with a dirty filter or a dirty coil or the registers in all the rooms are not open, in other words not enough air going across the heat exchanger.

When this is the case the furnace lights and runs for a short time and then the fire goes out but the blower continues to blow, the furnace then goes into a lock out mode and has to reset itself after about five minutes, after that five minute period the blower stops and the draft assist motor starts and the furnace goes through a new cycle.

This would fit you resetting the breaker and yet it was not broken because turning off the power to the unit will reset the lock out mode even if it has been less than the five minutes, so I think you were just resetting each time you did the breaker.

[labman]

If the gas comes on and quickly goes off, the problem is the flame detector. The best thing with any furnace problem is to go to the Sequence of operations in the Heating sticky,
https://www.askmehelpdesk.com/heatin...tml#post268970 Then after determining what is causing the problem, you can check other sections to fix the correct problem. If the control board doesn't get the signal from the pressure switch that the blower is running, the gas will never come on. A simple cleaning of the flame detector may be all that is needed.

[labman]

From a PM:
''I can find no flame detector anywhere on the unit. After reading some of the other info on this site I decided to locate and clean it, but there does not seem to be one anywhere on this unit. The problem seems to be either in the pressure switch/inducer blower since there is not enough vacuum to open the switch every time. All the ducts are fairly clean, has new filter and airflow does not seem to be a problem. Looks to me to be either the pressure switch has a bad diaphragm or the inducer is not producing enough vacuum. Otherwise it seems to me it must be in one of the boards. Any ideas?''

Does the gas come on or not? Or is it a sometimes thing? Before working on the flame detector, you need to have the gas coming on consistently. I am wondering with a couple of different intermittent problems if the trouble is a poorly seated plug where the control wires connect to the board, or dirty contacts. Try wiggling it around.

Best to keep everything in your thread in the forum. I am sure you have a flame detector, but can't tell you much more. You might make sure the air intake and vent pipes are clear. The vent could be full of frozen condensate.

[brubble01]

There is no flame detector on this unit anywhere. Vents are clear, ducts are clear, registers fully open. I have cleaned and reseated every electrical connection on the unit. As the unit is now, we are at or near the proper temperature, when the temp drops a little and the thermostat calls for heat nothing happens until I manually operate the pressure switch, there is not enough vaccuum created by the inducer to operate the switch. I don't know exactly how much vaccuum should be required to operate the switch, Either the pressure switch unit has a bad diaphram or the inducer is not creating enough vaccuum to open the switch. I have the switches plunger taped closed and when the thermostat calls for heat and it doesn't come, because the switch has not closed and then opened again, If I manually close and then open the switch again the igniter glows, lights the burners and it runs fine until the next time the thermostat calls for heat. At that time I must repeat the above steps. It seemed to me to be several different problems as time went by, but have pretty much decided it must only be the pressure switch or inducer causing all the problems. There is no flame detector on the unit, the harness from the control boards go to the rollout switch then to the limit switch in the heat exchanger and then back to the control boards. The next harness comes from the boards to the gas contol unit and then back to the boards. The last harness comes from the boards to the pressure switch and then back to the boards. I don't know all the different designs of furnaces, but this one was designed without a flame detecter somehow.

[labman]

It can't cost that much. Why don't you try replacing the pressure switch?

[brubble01]

Thanks for the reply, am planning on doing so Monday, now that I've narrowed the problem down a little today. I looked online for the switch unit and of course it's available from many online sellers, but they want anywhere from 150 to 210 bucks for what should probably cost around 30 bucks. Just like the limit switch was around a hundred bucks online, but I found one at a supply store locally for 25. Thanks again for the reply, I'll get it going soon, I just wish I knew for sure how much vaccuum the inducer should create so that I would also know for sure if it is the switch or the inducer itself.

[T-Top]

On a 90% furnace if you have a restriction in the vent or condensation line the pressure switch will not close. Check the drain for restrictions(blow it out with air or use shop vac.) or it may be a drain freezing with the cold temps.

[letmetellu]

Sounds like you have to problem solved so all you need to do is to find a switch. Do you have a vacuum gauge? If so check the vacuum and see how much you have from the motor and then measure how much pressure you have to but on it to open the switch yourself and then compare the numbers... that should tell you something. I have never had one of the switches go bad. I have had motors go bad because of bearings or the blower wheel would come loose and rattle. Good luck

[benny101]

I know this is an old post, some one please help me... I have the same problem... Brubble01, did you solve your problem by replacing the pressure switch?

[donbunker900]

I have a Ruud Silouette II furnace that occasionally will not come on at all. If I tap on the pressure switch lightly it starts right up and works for a week or two. I am tempted to remove the pressure switch and try to clean it out as well as blow the flue out. The furnace is about 7 years old.

Anyone have any ideas or experience on this? Thanks.

[joey EG]

Here`s a thought. "cumbustion air". My furnace did the same thing. We would wake up to a cold house. After having a technition looking at it, replacing various components (like the flame sensor). We`ve had this problem since the unit was installed, and the installers didn`t pick up on this. Our furnace had been installed in a closet. The duct outlet leading into the ad and the exhaust outlet through the roof had been insulated and sealed, so, when the closet door is closed the exhaust fan would suck up all the air that was needed for cumbustion. When the burners would come on there was no air/oxegen left for the fire. When I moved the insulation away from the register leading to the ad, this seemed to help. I then added a louvered vent to the closet door. Problem solved... joey..

[2tawl]

I am a few years past 2007, but I have a 2 year old RUUD 95% model RGRC furnace which had many of the other fellow's problems. Intermittent blower activity before, during and after end of ignition. A cold house with cold heat from the warm air vents,etc. Called an HVAC technician in. Problem solved with removing debris from the condensate drain. 2tawl