Furnace fires without call from T stat

Jzobie

We have been having an issue with our Lennox oil fired hot air furnace for some time that none of the professionals have been able to fix. We started getting an overheating smell coming out of the registers and I found that the furnace is running without the fan running and heating up the heat exchange since the hot air is stagnant. First I replaced the thermostat as recommended by professional, no luck. Then we thought it might be a fan issue but I noticed that the furnace fires and runs with the fan fine when I hear the thermostat click and call for heat. The issue is that the furnace continues to fire and cycle (without the fan running) when the temp is above the set point. I read that it could be a short in the wire but then it would call for heat and the entire system, including the fan would run. When it does this, I have to manually turn the furnace off and let the temp drop below the set point then turn the furnace back on and it will usually run fine for a little while but it has been running without call for heat more and more lately (It used to do this once or twice a week, now it is multiple times a day). Any help would be appreciated. 

STEVEusaPA

Sounds like you didn't have a professional. Make/model # of Lennox?
I find it odd that the blower isn't running and someone replaced a thermostat.
Someone needs to check the fan/limit, board, or fan center issue, depending on what you have there.
Then check the capacitor and blower motor.

EBEBRATT-Ed

@Jzobie

What @STEVEusaPA said

You need a professional before you cook the furnace and need a new one. Check "find a contractor on this site"

mattmia2

STEVEusaPA said:

Sounds like you didn't have a professional. Make/model # of Lennox?
I find it odd that the blower isn't running and someone replaced a thermostat.
Someone needs to check the fan/limit, board, or fan center issue, depending on what you have there.
Then check the capacitor and blower motor.

Or starts a fire. i would not sleep in the house or leave the house unattended with the furnace running until you sort it out. My fear is that the relay for the burner may be sticking so it stays running when the controls are trying to shut it down.

Are there furnaces with timer only blower controls that will not turn the blower on with a rise in temp even if the burner is stuck on?

Jzobie

Turned out to be the AC ready kit. Thanks for the help. 

EdTheHeaterMan

I have never liked that part. Seems to be a weak link in a fairly good oil burner. Beckett should do some research on that part and get a better micro-relay in that thing. When I see that AC Ready Kit on an oil burner, that's the first place I look when there is an issue with the low voltage system. sometimes there is intermittent chattering on that micro-relay, sometimes there is just a plane failure "No Heat" and this is the first time I heard of the relay contacts welding shut, but I'm sure it is not the first time or the last time that will happen. In my opinion, the enclosure is too restrictive for that relay causing too much heat to build up over time causing the various failures.

Respectfully submitted,
Mr.Ed

Jzobie

Ed, I am glad that you said that you haven’t heard of this happening either because my trusted technician even called a few friends and none of them have encountered this issue. Finally nailed it down when it was making the issue (it was sporadic) and we disconnected the wire to the Gensys which caused it to stop immediately. Then the next time around a quick tap on the relay with a screwdriver when it was running without fan immediately stopped the issue. I do believe heat played a role personally. 

STEVEusaPA

AC Ready Kit...you are the weakest link. Yeah +1 with @EdTheHeaterMan. They are easy to check out when they completely fail, but a PIA to change out with all the wires, the small box, and the small space.
Carlin Kool Kit may be better, but no one seems to stock them anymore.

EdTheHeaterMan

@STEVEusaPA... I never knew that Carlin made something like that

Would have definitely used that product.
I hated to put on those AC Randy Kit when changing out a R8184M