Furnace with over-active igniter

[ikedae]

After years of lurking, I have finally come up with an issue that I have to post my own thread for!


I have a furnace that in the past couple days has decided to continue to click (sounds like the igniter) AFTER lighting. It lights up no problem, keeps the trailer nice and toasty. The clicking is not continuous, it occurs at fairly regular intervals that I have not timed because I usually notice it when I'm about half-awake. On occasion the fan will also shut off then start up seconds later. Re-ignites just fine (or stays ignited?), keeps blowing warm air.

I'm planning on trying to open it up later to see if there's anything in there that might be clogging up the fan or doing something... The outside vents have been meshed for years, so shouldn't be anything getting in that way, but I do have critters with copious amounts of fur. And my poor rig was neglected for 6 years before I got it (I've been fulltiming it for 3.5 years), so who knows what's going on in there....

I know I should give you guys the full specs of the furnace, but it's 4 AM and I don't feel like getting up yet, so I'll get to that later... 🙂

[RJsfishin]

I don't think its the stat, but its easy to jumper the stat, and eliminate it as the problem.
If its a relay clicking, its a bad connection, or a control board going bad.

[ikedae]

Further investigation, and the fact that I was standing in the middle of my kitchen when it started clicking again tonight, has revealed that what I'm hearing is actually the relay in the AC unit. Further searching on the forums does indeed suggest an oversensitive thermostat could be to blame. New thermostat it is!

[John_Joey]

ikedae wrote:
...Seems to run fine on high...

As in the thermostat never had the chance to turn the furnace off :W
I'm guessing at night the thermostat may cycle more often.

Also, if the fan is really coming on and off like you say, then there is a thing called a time delay relaythat might be the problem. Again I would wait till it failed to make debugging easier.

[ikedae]

Doesn't look like I got lucky, looks like it'd be a pain to get into.

I've been running it on high while I've been home today, partly to see what it would do and partly because it got cold after I turned it off when the clicking/shutting off and on was driving me nuts last night. Seems to run fine on high... I think I'll take the wait-and-see approach. Worst case I'll need to take it out and tinker with it when I'm unemployed and have nothing better to do with my life. 😉 Well, worst case I suppose would be having to replace the whole darn thing, but I don't think it's going to go that far...

Thermostat has been on my to-do list for a long time anyway, so I'll probably go ahead and do that in the near future.

Thanks for the help!

[ScottG]

I may have misunderstood, if it's just sparking for a while after it starts then that's normal and is what I was talking about.
If the fan is shutting off and starting right back up again then that's an issue.

[John_Joey]

From what I know most Suburban furnaces have to get pulled out of the trailer to repair them. Maybe you got lucky and have one that has an outside access panel.

If you didn't get lucky then the only thing you can easily check will be the limit switch on the back. That should be good, because if it was really bad the furnace would not light. Everything else will be on the opposite end of the furnace where you can't get to it.

IMO, given what you said, and the fact that it's intermittent, I would just live with it until the component broke. It will make finding the problem much easier. I still might consider swapping out the thermostat since they are cheap and easy to do. Just pull the 12v fuse from the panel prior to changing it out.

[ikedae]

I do think it's normal to her it click several times when it first starts, but this is after it has been running a while, long after it has warmed up. The shutting off and restarting within seconds bit is definitely not normal behavior, and is when I notice the clicking most. Though that may be because my furnace typically runs at night, and the shutting off and restarting sometimes wakes me up, so I'm awake to hear it.. Or makes me pay more attention.

[ikedae]

It's a Suburban furnace. Not sure of the exact model number, as the only number I can find is on a compliance sticker of some sort that has 15 model numbers on it.

This is definitely not normal behavior. I was thinking something electrical as well, thermostat makes sense.

I'm learning this all as I go, and thus far have not had to troubleshoot my furnace (which I only use a few months out of the year anyway). Moved into my beast right out of college, so there has been much to learn! I'm hoping for a cheap and easy fix, since I'm about to be unemployed again... The good news is that it still heats, but I also don't want to damage it further or make it explode (which I suppose could fall into the further damage category) or something.

[Mike_LeClair]

Does this particular furnace have a flame sensor? If so it could just need to be taken out, cleaned and then returned to service.

Mike

[John_Joey]

The OP is a FT'er who has lived in his rig for awhile. I'm guessing that he is hearing something that is not normally what he's heard before. Implying there is a problem, and not just some safety feature kicking in. He would have heard that a hundred times before.

IMO, it is electrical, and more then likely a bad connection somewhere. The connection is telling the furnace to shut down then the connection becomes active again and tells the furnace to keep running.

The reason I thought the thermostat is because I'm thinking the points in the thermostat are bad, a bad thermostat wire, or the thermostat is so old it reacts too quick when it hits the on/off temperature.

Of course it can be many other things also. Might be a dirty connection on the board, gas solenoids, or somewhere else.

[ScottG]

Ozlander wrote:

ScottG wrote:
It's a safety feature and it's normal.

NO IT IS NOT.

Yes, it is.
The last two furnaces I've had did the same thing since new. I asked a RV tech about it and he said something about it keeping the furnace from exploding if it didn't light properly because of a thermocoil or something.
I suspect it continues to spark until the thermocoil gets hot enough to let the system know there's a flame - but thats just my SWAG.

[Ozlander]

ScottG wrote:
It's a safety feature and it's normal.

NO IT IS NOT.

[ScottG]

It's a safety feature and it's normal.

[John_Joey]

The more I thought about what you said, the more I'm thinking it could be your thermostat or it's wires being loose. Thermostat's are cheap and easy to replace, so you might want to think about that also.