Needing help with propane furnace.

Imminer2 · May 18

My house furnace will only start up with the inducer fan inlet line disconnected at the fan. Once started, it will continue to operate when the line is reattached. I've had the inducer fan inlet and outlet lines cut open, inspected and cleaned, flame sensor replaced, gas valve replaced, inducer fan/motor/capacitor replaced, pressure switch replaced, all tubing checked, condensate pump cleaned and tested. The control board is next. The system is not new. I've had a professional technician work on it and they were not able to find the root cause. Any help would be appreciated.

mattmia2 · May 18

tee a monometer in with the pressure switch on the inlet and outlet and see what is happening. which switch does the control say it is faulting on?

109A_5 · May 18

Make and model of the furnace may help us help you.

Imminer2 · May 18

Make and model information: Bryant 90 Plus HVAC system model 350MAV036080 serial number 350MAV036080ADKA. Code 34 ignition proving failure.

EdTheHeaterMan · May 18

NEW SYSTEM? has it operated properly at any time after installed? This ia a multi position furnace. As a result, the condensate lines may need to be reconfigured to accommodate the removal of condensation from the secondary HX. If not properly configured the pressure switch may not operate when required. You will need to use a manometer in line with the pressure switch tube to see what is happening when the actual failure is happening.

Or you can just keep shooting the parts cannon and hope for the best.

Have you paid for these repairs? Did you use a credit card? Perhaps you can dispute the charges. You paid to get the heat operating. It is not operating. You did not get what you paid for. You have a case to have the credit card company charge back the vendor.

mattmia2 · May 18

what were the results of the combustion analysis? what does the flame around the flame rod look like? what were the gas pressures? is the bonding from the burner back to the control good? is the wire to the flame rod good? does the inlet and exhaust piping meet the instructions in the manual?

the error you are getting is "ignition proving error" so it is locking out because it isn't proving flame. that probably means it is changing how it is burning when you remove the additional resistance of the outside inlet piping. it could be whoever adjusted the combustion didn't do it properly, it could be the gas pressure is low, it could be the content of the gas changed, it could be that the inlet and exhaust piping doesn't follow the instructions.

EdTheHeaterMan · May 18

Code 34 can be a result of the flame never igniting or it can be that the flame ignited and the sensor did not sense the flame. Can you see if there is a flame or not? Usually the error code would be different if the pressure switch were the problem.

JUGHNE · May 18

I assume you are talking about the PVC, 2 or 3" inlet.

Show a picture of the piping of the furnace with the door off please.

Imminer2 · May 20

The inlet line is to the left and just above the gas valve. To restate the issue: the system will start up with the line disconnected. Once it starts up I can put it back in place and it will continue to operate.

Several comments regarding my approach about replacing parts… I found a supplier that accepts free returns with no restocking charge. To date no real expense incurred. I've been doing the work myself.

I have a replacement control board which I will replace next.

SuperTech · May 20

That looks like one of the Carrier/Bryant furnaces that are notorious for the secondary heat exchangers failing. I would suggest getting a combustion analysis performed on the furnace before you sink any more money into buying replacement parts for it. It's possible that the parts are doing their job and the faults are an indication of a greater problem with the heat exchanger.

mattmia2 · May 20

https://forum.heatinghelp.com/discussion/comment/1855967#Comment_1855967

Who did the combustion analysis after the gas valve was replaced?

Look at the flame when the blower starts, there should be no change, if there is the hx is definitely bad. Even if it doesn't is could still be the hx.

pedmec · May 20

You really can't tell a cracked heat exchanger on a 90 plus furnace by looking at the flame. The combustion side of the heat exchanger is in a negative pressure zone so it really just mixes the blower air that is getting into the combustion side with the combustion gases. the one way to tell is if your O2 numbers keep increasing during your combustion analysis. It will keep creeping up when the blower runs.

HVACNUT · 10:20AM

Can you post a pic of the wiring diagram? I can't find one that used the GP relay.

Screenshot_20250521_061239_Samsung Internet.jpg

The only diagrams I found show the pressure switch wired directly into the board.

Does the serial number on the evaporator start 4688? Is it as old as the furnace?

EdTheHeaterMan · 5:40PM

That looks so familiar. I think I had a customer with that same problem back in the day. I don't remember exactly how I resolved the issue but it was nothing to do with the flame sensor, gas valve, inducer fan/motor/capacitor, pressure switch, the tubing, condensate pump, or the control board.

I have a distinct feeling that it was a result of the way the combustion air flowed across the burner that diverted the gases away from the igniter. I think the fix was to adjust the position of the ignitor, but I could be wrong about that because it was so long ago. That is a vintage Carrier product. Many of them have been replaced by now.

Needing help with propane furnace.

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