Needing help with propane furnace.
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.
Comments
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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?
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Make and model of the furnace may help us help you.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
Make and model information: Bryant 90 Plus HVAC system model 350MAV036080 serial number 350MAV036080ADKA. Code 34 ignition proving failure.
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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.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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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.
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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.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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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.
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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.
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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.
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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.
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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.
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Can you post a pic of the wiring diagram? I can't find one that used the GP relay.
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?
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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.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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I changed the gas valve, control board and checked on the position of the igniter with no success. Furnace still only starts with the inducer fan inlet pipe disconnected. Back to using the original gas valve.
With the inlet pipe off I would think that there is more air flow, but less vacuum (ie. higher pressure). It doesn't appear to affect the startup electrical sequencing since it starts the igniter and opens the gas valve. I think the essential question is why does it ignite the gas under the abnormal condition and not under the normal condition? It's not a blockage in the inlet or outlet lines since I cut them apart and inspected the whole length of both.
Oh by the way, when the technician left he said to just run it with the inlet line disconnected. That didn't seem to safe to me, so I have not run it that way except for trouble shooting.
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you need to find someone that understands combustion. it is wrong either because it is out of adjustment or the hx is clogged or compromised.
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I had a Trane that experienced random-ish lockouts due to the pressure switch opening, in spite of everything being in spec. Trane tech support condemned the HX even though it didn't fail any tests.
I currently have a 2 stage 90%er that won't operate at high fire, the flames start pulsing & the controls lock out. Removing the intake allows it to run fine (BTW, there's no issue running it without the intake if the IOM shows that as a valid configuration). Since the furnace is in a temp location, I haven't worried about it, the intake & flue will be changing once it moves in to its final location.
Fluid dynamics is hard.
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What is the deal with the furnace being installed in a temp location?
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Gut job remodel I started in the winter. Basement is getting a mech room but I needed heat, so I just set it near where it goes. It'll shift a foot or so once the walls are finished & I'll rework the flue & intake. If ti still has issues, I'll figure it out then.
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that furnace was never designed for temp heat during construction. All that dust and dirt is plugging up everything. I don’t even think it’s worth throughly cleaning. Replace it!
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There's no dust & dirt in it. This is a personal project for my little brother, not a flip. I've got time to do it right.
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there is no way you ran that unit during construction and don’t have it filled with Dust and dirt!
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There are a number of precautions that will preclude the furnace being filled with dust and dirt, chiefest are not operating it during or after producing dust and keeping a clean filter on it.
I was going to say it's clean enough to eat off of, but that sounds a little snarky and slightly hyperbolic, which I'm trying to avoid. Seriously, it's no dirtier than any other furnace that's been run for a few months.
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pull the squirrel cage and take a picture
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You have a bad / plugged (or partially plugged) secondary heat exchanger. That furnace is part of a recall from many years ago. There are options within the recall to replace ht exc, but it really isn't worth it.
It's time to replace the furnace.
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that plastic trap, you might wanna pull the hoses and pull the trap and blow through all that drainage stuff. I worked on that same furnace this past winter, it was plugged solid. Everything worked beautifully after that.
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Thanks to everyone that commented. This unit is 25 years + and we are looking at replacing it with a new unit. Maybe opening a can of worms, but what brand to people recommend?
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the installing contractor makes or breaks the equipment.
worry about there name not the name on the box’s.1
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