# heat will not trigger fan



## qkedarg (Feb 24, 2016)

I have very old rheum ugdg-12earjr furnace serial starts with CW with forced air, gas and ac. At one point we noticed out heating was intermittent. i don't know why, but when he came it didn't seem to be lighting. I called hvac guy who came, swapped out ignitor, charged me 400 bucks, then said that didn't fix it, and it must be my board. 700 dollars for a new one. and if that doesn't fix it 4k for a new furnace... and i won't get my money back. so i try the board myself. I'm not a HVAC guy, but more than capable of doing this. promise. 

so i look online, i think i find the right board. (90$) I've tried two boards so far. The icm 288 which is for rheem part 62-24048-82 and the protech part 62-24268-03.

Both work for everything with one exception. They do not turn the fan on when the heat turns on. Everything else works. Fan with ac and fan manual. But u can't even jumper the g to r if heat is on. It does not turn on when w is hot. There is no current on the g line when heat is on and u can't even turn on the manual fan w the thermostat. The heat overrides it and turns the fan off. The heat limit switch turns the gas off after about 20 seconds because the fan is not working. (by fan i mean the main air moving blower, the gas exhaust fan works as it should) 

It doesn't seem to be the thermostat because jumpers don't work. And it's not the setup - no fan prong connection on the board has 120 v at any point when heat is on. Except every now and then the fan turns on after the heat limit switch turns off the gas. this happens occasionally. I'm sure my problem is the board. But I have not idea what one to get...

Interestingly, i have another furnace different model, but same year and brand. and when heat is on with it, i.e. w is hot, g is also hot. and it works fine. i even tried pro programing the nest to control the fan when heat is on, and this also does not work. the board clearly will not accept a g current when w is hot.


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## qkedarg (Feb 24, 2016)

After a little further eval it looks like the problem may be that the new board requires a flame sensor be wired in ... See if that works.


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