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dabrooks · 01-29-2023, 08:02 AM

We have a 2013 Tiffin 35QBA with two gas furnaces. The rear one works fine. The front one which is also connected to the same thermostat as the heat pump is not working.

Issues started back in November when the furnace stopped working during the night. It was our last night in Tennessee so I waited until we got home to trouble shot the problem. When we got home it worked fine.

I took the RV to a repair shop for a couple of other issues and asked them to check the furnace. They tried it several times and it worked as intended. They even moved the wires around while it was running to check for loose connections.

I brought the RV home and tried the furnace several times the week before we left for our trip and it worked fine. The morning we left I went out and started the furnace it came on. When I went back out it was off and had only raised the temperature a couple of degrees. We left home and an hour later I stopped at a store. I turned the furnace on and it came on and warmed up to the set temperature and shut off.

Since then the furnace worked a couple of times but now it will not come on. When I turn it on I can hear a click at the thermostat. My wife also hears a click at the furnace but nothing comes on.

The heat pump and AC both work fine.

Any suggestions?

Old-Biscuit · 01-29-2023, 09:12 AM

Fan must start before ANYTHING else can happen

Click at Thermostat........t-stat has closed and is sending DC back to furnace circuit board

Click at Furnace.......circuit board has gotten DC back from t-stat (at PWR connection) but is Not sending DC to Fan Motor (From BLW connection)

Bad relay on circuit board......

Provided RV DC VOLTAGE has been normal vs low system voltage

dabrooks · 01-29-2023, 09:32 AM

Thank you for getting back to me so quickly. DC voltage seems fine in the RV.

It appears that I have to pull the furnace to replace the circuit board. I don't think I will need the furnace here in Florida so I am going to wait to pull the furnace when I return home on February 6th. Meanwhile I will do some research and order the correct circuit board.

I most certainly will repost when I pull the furnace if I need help.

Thanks again.

dabrooks · 02-06-2023, 03:12 PM

Got home from our trip yesterday. The board I ordered was here so I installed it this morning. I did not have to pull the furnace. Turned the 12volt power back on and set the thermostat for gas heat and the furnace fired right up.

Thank you Old-Biscuit for your help.

Old-Biscuit · 02-06-2023, 06:20 PM

Have you put it thru it's paces?
Let it reach t-stat set point, turn off then restart when temp drops below t-stat set point

Glad to be of help!

dabrooks · 02-06-2023, 07:04 PM

I only let it warm up to set point and shut off. I opened the door and when the temperature dropped it came on and heated back to the set point and shut off.

I will do some further testing tomorrow.

dabrooks · 02-07-2023, 12:40 PM

Tried all different scenarios and the furnace functions as intended.

When I first looked I thought I would have to pull the furnace but on our Tiffin 35QBA I did not. The wires were short on the connector so I had to get it disconnected before the board would come out.

Thanks again for your help.