Hello folks ! Just found your site while looking for answers to my furnace problem. Signed up as I think this site will be very helpful with home repairs.

My problem: I have a modular home. New 15 years ago. Furnace is A Miller M1MB0771BW. LP fueled. I had an issue, I believed, with the pressure switch as it was hanging closed. Changed it out and the new switch would not close at all. So I put a new inducer motor in though it didn't seem like the old one was bad. That did nothing to clear the issue. So I bought another pressure switch. This switch will work, sort of. What happens is the regulator clicks as it opens and closes continually in a few second intervals. Due, I'm sure, to the pressure switch not holding closed. So I read where there could be air flow issues both in and out of the furnace. So I cleaned the intake above the inducer motor. Then up to the roof. I had a roof installed a few years ago due to snow damage. The contractor half assed the roof jack when they replaced it. So I purchased and installed a new nordyne extension pipe set and a new topper. Vacuumed out the exhaust side with my shop vac. looked pretty good. So back inside to see if all is well. Same problem. The switch will close and once the burner lights, the clicking starts as the regulator opens and closes.Don't have a lot of hair left to pull out. This is what I managed to determine and it is what I need you folk to help me with.....Once the furnace lights, if I hold open the little viewing door the furnace igniter will run, no clicking of the regulator, pressure switch is closed and all is good in the world. Close the viewing door and right back to the on/off issue. It would seem that the exhaust air flow is being limited. Any way to clean/clear the exhaust ? Or am I just wrong. Thanks !!! John

 

Unfortunately, many quite different things can cause the pressure switch to fail to make.

The trick for a DIYer is to check out as many possible causes of the problem as possible without spending money and time on replacing expensive parts...

You seem to be a convert to this approach!


For openers, I'd inspect the rubber tubing from the inducer motor housing to the pressure switch. look for holes, cracks water or other possible problems.

The inspect the fitting that the hose fits into at the inducer motor housing. It can get plugged with corrosion. Use a suitably sized drill bit to be sure that this fitting is clean. Often a smaller drill bit is needed to get into the small hole into the inducer motor housing ---m be sure that the drill bit goes in far enough. Holding the drill bit firmly with pliers so that it doesn't drop into the housing is recommended.

Try disconnecting the vent pipe at the furnace and see if the furnace will operate in that condition AS A TEST.

If none of that helps, usually the inducer motor assembly can be removed fairly easily from the furnace. Remove the assembly and inspect the fan for being plugged with debris or damaged. Spin the inducer motor by hand and see if it's stiff or hard to turn. Power up the inducer motor and see if it easily comes up to speed.

Inspect the heat exchanger you can see when the inducer motor is removed. Look for accumulations of water or debris.


These are all checks that can be made fairly easily by motivated DIYers and are likely to turn up many of the issues that might be causing the problem. No outlay of cash needed or waiting for parts that aren't the problem!

Around here, we promote the idea of systematic diagnosis of problems rather than guessing and supposing. Hope that approach works for you!