Having an intermittent issue with our gas furnace, it only gets used a few weeks a year ( Florida ), but would be nice to sort it out. Only two service guys in the area I trust, one won't touch gas and the other has looked at it already. ( worked fine while here, shocking lol ) He put a new blower motor in the air handler this past summer and the issue started the first time we used the heat this winter. Ruud Silhouette II gas furnace Draft motor starts and runs. Ignitor glows. Main burner lights. Problem starts here, burner stays lit for a few seconds then goes out. About half the time. If I kill power to the unit for a while then restart, it will work as it should. Could be one or 10 cycles later, problem comes back. I've cleaned the flame sensor and checked over for obvious wiring issues. Should I just get the IFC replaced and be done with it or is there something else I should look at first? Thanks!
Possible air leak causing the gas valve to shut down? The newer units all have some sort of safety now. I had to replace mine a few years ago.
Flame sensor or maybe the vacuum sensor thing (can't remember the name) that checks for draft. I have the same furnace and had the same problem. Take off the rubber tube and blow through it to make sure it's not blocked. Then rap the backside of the thing a couple times with a screwdriver handle. Sometimes they suck up gunk and get blocked but it won't shut down until after the flame is lit. Mine would run for about a minute and then shut off.
Sensors are like $10 at Amazon. Buy two - keep the second one taped on a wall near the furnace for use when the replacement fails.
Nothing coarser than a fine scotch brite pad should be used to clean a flame sensor. No need to get a replacement. It can’t fail unless it physically breaks. It also can’t be “jumpered”. It’s a rectification circuit. That rod gets 60-90vac from the control. Flame conducts electricity and rectifies it. The board is looking for a tiny amount of current to flow to ground, between 3-7 DC microamps (uA) anything below 1-1.5uA will shut down the furnace. “Micro” in electrical terminology is “millionth”, so it doesn’t take much of a coating to make a difference. Since you already cleaned the flame sensor, it sounds like the pressure switch may be opening. Make sure there is no blockage in the flue or flue connector, and stick a tiny Allen wrench in the port on the inducer motor to ensure it’s clear. The switches do fail, but more frequently it’s doing its job and isn’t observing adequate vacuum for some reason.
Cleaned flame sensor with 0000 finish steel wool. It's a very very smooth surface so didn't want to use anything course. Checked hose and path into draft motor, nice and clear. There's very little pull on the line so assumed the inducer was extremely sensitive and didn't go poking in there at all. I'll take a peak at it. Thank you for info!
What happened to my gas furnace at the beginning of this winter: Turned out that my filter was clogged too much, and causing the 'roll-out' switch/sensor to shut it down seconds after the burner fired- just like you said. There is a little button on the small 'roll out switch' to reset it. We reset it, got a new filter, good to go. We're going to be in the 20'sF for the high for the next 10 days
Check incoming out outgoing pipes. One year humidity caused my intake to frost up so bad it restricted the airflow and the furnace wouldn't run. I had to move the two pipes farther apart.
Damn, I just got to replace my furnace because the heat exchanger coating started to burn off. Good thing it's been damn cold here this last week.
Great.. My guess would have been (and was once) dirty flame bars. Once the sequence starts the flames move from the igniter to the last flame bar. That has a safety that must get hot enough to prove to the board that we do have flame and leave gas on. Since the bars are in the air flow while the air conditioner runs dust builds up. Pull the bars, soft brass brush and put them back in. Besides the basic checkout that is the biggest thing they do for furnace PM.
