@JBraun I think my stupid furnace is on the way out. It's 20+ years old and I have had service calls on it the last couple winters. What it's doing now is running for a second, lighting off, then stopping. Then it comes back on, runs, lights, and then it usually stays on. I've had the issue before where the sensor needs to be cleaned with steel wool, but in that case it would never light. I've also had the batteries in the thermostat die and that screwed it up, so I changed those. When I woke up this AM it was 6 degrees colder than I had it set at. I'm not sure what to do. I'd rather not pay for a service call if I'm just gonna end up replacing the fucker. The last repair was a circuit board or some shit to the tune of $250. I kind of remember the tech saying something to the effect of this is the last repair before it's time to replace the whole thing. How bad am I gonna get slammed price-wise? I have a very small house (850sq ft) so I can likely purchase the smallest available unit. What brands do you recommend? Any other advice would be great. This sucks.
If the furnace is firing then shutting down, I'd start with putting a new flame sensor in it. That's $12. You won't get a flame at all if the pressure sensor is erroring out. You may get a flame that dies if the gas valve is going bad. If it fires and runs after erroring out the gas valve is probably fine. Just had to replace the control board in my furnace. Woke up to 63 degrees on Friday morning. Inducer fan would twitch and error out on pressure switch. After a dozen attempts it would finally run the inducer but it wouldn't flame, so I knew the inducer was fine and the pressure switch was fine. $80 board and it's toasty warm again.
I'm getting a flame. It 'spools up', lights off, and then shuts off like 5 seconds later. Then it tries again, and it usually works fine then. Sometimes it takes it a few tries.
Flame sensor. Start there. If it still craps out after that find out what the warranty on that control board is.
I know very little about this stuff, but depending on how old the burner is, I replaced my "intermittent pilot/spark ignition module " and that solved the same problem you had.
Hey Scotty. Sounds to me like the flame sensor is dirty again. The unit has a five second trial for ignition, so if it lights properly but the control does not identify flame, it will think it isn't lit and shut down. Most units will do that three times before they lock out. A flame sensor is a rectification circuit. That flame rod gets AC voltage from the control. Oddly enough, flame conducts electricity, but does it very poorly and rectifies it to DC. The control is looking for at least 1.5uA (microamps), which is 1.5 millionths of an amp, so any thin layer of anything will stop it from sensing flame. If it sees less than 1.5uA, it won't stay running. Don't bother replacing it unless it's physically broken. Nothing there can fail, all it is is a metal rod with an insulator. You could make one with a coat hanger and it would work. Get that thing running and we'll tackle your replacement questions.
Oddly enough, I went down there to pull it out and clean it but when I was just getting ready to pull it fired up. It's been acting okay since early this aft, so I haven't cleaned it yet. I will though. I think I'm on borrowed time though, I probably should plan to replace. The past couple summers now I've told myself to go ahead and replace it before I need to but for whatever reason I didn't. Now I'm a little concerned I'm gonna get my pants pulled down on the price since it's November in Wisconsin and I obviously sorta need a furnace lol. Thanks again for the tips everyone.
What is the proper way to clean it? In the past I've used emery cloth or like a wetsand grit sandpaper, but I watched a youtube vid and the guy said don't use anything that abrasive. He actually suggested a crisp dollar bill.
Yeah solvent works, otherwise steel wool or a scotch brite pad. Just make sure it’s fine enough to not score it.
The probe clean is an easy check, but as you have said has been done before. Could be multiple problems. I had three different HVAC companies out to diagnose my system and replace different parts, pressure sensor, temp probe, etc. My symptoms were same as yours and the lines to the pressure switch were the problem despite appearing clear when the techs diagnosed the system. The vacuum lines were hard to get to and passing some air, but were causing the on/off problems you are describing. It took one tech more time then should be spent to clear the lines enough to keep the system lit. If the probe isnt the problem I would get a couple cans of compressed air and unplug the lines from the pressure switch and blow them out thoroughly.
Yes. I know you don't understand physics or anything, but I'll give you the highly technical explanation. Big scratches bad. Little scratches ok.
That's a good answer that even I can understand. I was asking at least partially because folks seemed surprised to learn that a green scubby can scratch stainless.
