gas furnace lights intermittently

[robbeck67]

My 7 year old gas(propane) furnace does not work all of the time. I have replaced the flame sensor/ignitor assembly. They come together. When I watch with the cover off this is what I see.....there is a call for heat, I see the ignitor light up and a small flame at the pilot tube, the flame goes out and the ignitor dims a little bit. Then the pilot comes back and the ignitor gets brighter again. This happens a few time and results in either a click and the furnace lights or a click that is not as loud and the fan motor shuts down. There is a honeywell valve with the code 5 flashes and then one flash. I think it is a newer valve though. It is a 9541 and not 9500 which I have read had problems at the connectors. It can work for a week and then stop for a while. Very intermittent. Any help would be great.

[paul52446m]

My 7 year old gas(propane) furnace does not work all of the time. I have replaced the flame sensor/ignitor assembly. They come together. When I watch with the cover off this is what I see.....there is a call for heat, I see the ignitor light up and a small flame at the pilot tube, the flame goes out and the ignitor dims a little bit. Then the pilot comes back and the ignitor gets brighter again. This happens a few time and results in either a click and the furnace lights or a click that is not as loud and the fan motor shuts down. There is a honeywell valve with the code 5 flashes and then one flash. I think it is a newer valve though. It is a 9541 and not 9500 which I have read had problems at the connectors. It can work for a week and then stop for a while. Very intermittent. Any help would be great.

You say you are getting a small flame at the pilot. Is it the normal size of the pilot, if not then your gas valve is not passing enough gas to the pilot or pilot is plugged some and needs cleaning out. If it is passing enough gas but not proving, then it would be in the flame rod, flame rod wire or in the electric
board. Try using a little fine sand paper on the flame rod, even if it looks clean. They get a coating on them that you can't see. Later Paul

[robbeck67]

Thanks for getting back to this ? on Christmas Eve. I know it's a busy time for most people. Not sure if the pilot size is normal since I've never checked it before the problem arose. I'm thinking it is OK. I just realized how this system works. I was thinking the ignitor lit the main burners. But it is the pilot that does that. The reason the ignitor goes on and off is that it has to keep re-lighting the pilot. I hope I'm right about this. So apparently the problem may lie in that the pilot is going out.

[paul52446m]

Thanks for getting back to this ? on Christmas Eve. I know it's a busy time for most people. Not sure if the pilot size is normal since I've never checked it before the problem arose. I'm thinking it is OK. I just realized how this system works. I was thinking the ignitor lit the main burners. But it is the pilot that does that. The reason the ignitor goes on and off is that it has to keep re-lighting the pilot. I hope I'm right about this. So apparently the problem may lie in that the pilot is going out.

that what i was telling you in the last post, and i gave you the most possible
reason. It could also be a bad contact in a roll out switch, or a pressure switch.
Check all hoses on pressure switches for cracks or bad on connections.
Later paul

[robbeck67]

After much tinkering and even chatting on the phone with a local repair guy, I think the problem is finally solved. I got a lot of advice but none of it seemed to quite be the answer. It really sounded like the flame sensor, but I had put a new one in and it didn't help. So I took the old flame sensor and bent it downward. It is now more of a right angle then the previous half Y shape. Ever since I did that and put it in, I haven't had one problem. It has started every time since. Hope this might help someone else out there.

[robbeck67]

The bending of the flame sensor was only a quick fix! It would still take a while for the main burners to come on. I finally fixed it after seeing a video on youtube of a guy cleaning the pilot orifice for his fireplace. Same thing is in my furnace. After unscrewing the pilot tube from the bracket, the pilot orifice (a tiny brass fitting that looks like a little nozzle) will come out. This is what the gas blows through. The pin sized hole in this gets clogged. You can clean it by removing one strand from a wire brush and using needle nosed pliers to push it through the hole. Wiggle it around making sure the opening is clear. Never stick something big through or the hole will get widened too much. After doing this use compressed air to blow out the orifice. This step may not be needed though. Put it back together and try it out. It has my furnace purring like a kitten.