Heating, Air Conditioning, Fridge, HVAC/Furnace problem



I have a Rheem Classic 90 Plus furnace model RCBA3765GG17 serial M0698 installed in 1999.  

For the past year the furnace has intermittently made a loud
popping / banging sound just after the purge fan comes on, sometimes in pops / bangs 15 to 20 times rapid fire like just before the main blower starts and sometimes after the main blower has be on for 30 seconds to a minute.  The noise is loud enough to wake us.  The Rheem repairman was able to duplicate the noise as the solenoid in the gas regulator and replaced the whole unit but it still is making the noise.  Just the other day it banged 20 times and that was after the main blower came on.  The repairman says  the solenoid is getting a signal  to fire but he doesn't know why.  He has also replaced the thermostat, cleaned the burners, cleaned the drain tubes and vacuumed out the air tubes but the problem persists but he assures me it isn't dangerous.  Do you have any idea what the problem may be. Thank you for any advice you can give.

It is hard to without hands on after you have had the unit looked at to come up with something.  My thoughts are that the problem happens when the unit is cold and it starts to heat up.  It could be in the unit, the flue or the ducts.  Try turning the unit on and off with different times between cycles.  You might find it only does it if the unit has been off for a while.


Heating, Air Conditioning, Fridge, HVAC

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Craig HVAC Expert


I have been in the HVAC field for the past 18 years. I can help with most HVAC questions. I work on commerical buildings for the most part, and have yet to find anything I could not troubleshoot and repair, when repairable. I work on small 1 ton units to a 2500 ton chiller. Troubleshoot air flow, elect, and control problems. I attend regular classes to keep up with the latest and greatest.


I work on commerical sites, hospitals, gov't buildings. I can troubleshoot just about anything in the HVAC business.

5 years trade school, VFD training classes, Liebert factory training, some York and Trane factory training.

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