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Tim H.
Tim H., HVAC Professional
Category: HVAC
Satisfied Customers: 3971
Experience:  Experienced in all aspects of HVAC, both residential and commercial.
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I have a Comfortmaker RPJ II furnace. It wont heat. The

Customer Question

I have a Comfortmaker RPJ II furnace. It won't heat. The induction motor runs and runs. I don't see the ignitor light. But, I don't hear the click before the ignitor should light. Does that mean the pressure switch might be bad? How would I troubleshoot this? Thanks.
Submitted: 5 years ago.
Category: HVAC
Expert:  Tim H. replied 5 years ago.

Thanks for giving me the opportunity to help! The fact that the inducer motor is running, but the unit won't go any further could signal:

1) bad pressure switch

2) kinked or disconnected pressure switch tubing

3) plugged intake or exhaust (you didn't give me a model number so I don't know if this is an 80 or 90% furnace-full model number would be helpful)

4) slow or defective inducer motor

Customer: replied 5 years ago.

Yes, I understand the suggestions you've made. Those are the ones I've seen from my previous internet research.


I've removed the ends of the tubing from the pressure switch. And, I placed a suction on the tubing and heard the click from the switch. However, the suction I'm placing on it may be more than usual and not be a good diagnosis.


The model number is a EnviroPlus90.

Expert:  Tim H. replied 5 years ago.
The full model number will be found on the inside of the furnace (top door) on a tag. I prefer troubleshooting with the full model number. One of the four items I mentioned above is causing this issue. You need to eliminate them one by one.
Customer: replied 5 years ago.

The model number is GUK100N16C1.


The tubing isn't kinked or disconnected.


The exhaust appears to be clear.

Expert:  Tim H. replied 5 years ago.

Is this a bit older furnace? If so, these had issues with a crack on the secondary heat exchanger if it was never replaced. Sometime the secondary would even plug up with soot. Check your primary heat exchanger and look for any signs of soot. Unfortunately, inspection of the secondary heat exchanger is quite a job and probably best performed by a qualified HVAC technician.

Customer: replied 5 years ago.
This furnace is about 15 years old. I'm not sure exactly what a heat exchanger is. I've opened up the panel on the front of the burners and took a look in there. They're little corroded, but really nothing unusual for 15 years of service.
Expert:  Tim H. replied 5 years ago.
I would suggest having this checked by an HVAC professional. The Heil and Comfortmaker (earlier models) had a tendency for the burners to rust over and this in turn would soot up the primary heat exchanger. Also, as I mentioned previously--the issues with the secondary heat exchanger cracking.
Customer: replied 5 years ago.
I already suspected that I might need a HVAC service person. The purpose of my question was to troubleshoot and repair the furnace.

Suggesting that I need the furnace serviced doesn't provide much value. My comments are nothing person.
Expert:  Tim H. replied 5 years ago.
Because I feel this may be contributing to the pressure switch issue. The heat exchangers (and the air flow of combustion products through them) are part of the way your furnace "makes" the pressure switch.