Trying again for help. Rheem 80+ forced air NG heater turns off within a minute of blowing heat with draft motor continuing. Cleaned flame sensor and pilot thermocouple. Still the same problem. Can't find any sensor lights. The furnace is over 15 years old so maybe they did not install such then. Turned thermostat up, draft motor spins, pilot lights, then burners, and after a minute or so the blower gives us heat. Within a couple minutes the blower and gas turns off leaving the pilot light and draft motor on forever unless I turn the thermostat control down or off. Have to wait several minutes to turn the thermostat auto on and the above cycle starts all over again. If I do not wait long enough to turn NG furnace back on just the draft motor and possibly the pilot light (I think) comes on. What would cause heat to turn off while draft motor continues but not restart until thermostat is turned off and back on after a few minutes?

Sounds like yer unit is locking out and you're resetting when interupting power, vent mtr. Running during lockout may be normal on this unit.. check sensor (flame), inspect pilot flame while unit is running..

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Originally Posted by drburdi

Trying again for help. Rheem 80+ forced air NG heater turns off within a minute of blowing heat with draft motor continuing. Cleaned flame sensor and pilot thermocouple. Still the same problem. Can't find any sensor lights. The furnace is over 15 years old so maybe they did not install such then. Turned thermostat up, draft motor spins, pilot lights, then burners, and after a minute or so the blower gives us heat. Within a couple minutes the blower and gas turns off leaving the pilot light and draft motor on forever unless I turn the thermostat control down or off. Have to wait several minutes to turn the thermostat auto on and the above cycle starts all over again. If I do not wait long enough to turn NG furnace back on just the draft motor and possibly the pilot light (I think) comes on. What would cause heat to turn off while draft motor continues but not restart until thermostat is turned off and back on after a few minutes?

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Start by testing the high limit controls. Make sure all the registers in the house are OPEN and check to be sure the air filter is clean and the return air not obstructed.

Air filter clean with no return obstructions. Where do I go to find what and how to test high limit controls?

Wiring diagram on the back side of the furnace blower motor access door. Use standard test procedures using a meter.

Yes I have seen that and verified that I have a flame sensor. But do not know what are the high limits are whatever the controls are. Is there a thread or site that shows what to test and numbers to get?

Follow the wiring to find the limits. ALL that info is stated on the wiring diagram. I do not have a wiring diagram for your no exact model number unit. Sorry