Weird Furnace problem - need help

[Guapotims]

2012 Flagstaff Micro Lite 21 FBRS History: Bought by Original owner in March 2012. Tried Furnace once and it worked fine. Not used again until I bought unit in Jan 2013. I tried furnace and it wouldn't blow or ignite. Was told to keep trying to see if it would eventually start (possibly needed to be worked and used some) Intermittantly began working, maybe 1 in 25 try's. When it worked, everything happened like it should have. Fan came on, igniter started then heat. shut off worked as it is supposed to. Igniter quit, fan blew for a few minutes.

Now, tonight I go out to try it again. I found that when I give the metal cabinet a slap, it all works as it should. Only occasionally will it start by the thermostat. Most times I have to turn on the thermostat and slap the metal housing. This works everytime.

My question is: What part would need this jarring to start it working. I have tried moving all the wires to no avail. There doesn't seem to be an "open circuit" in the wires (connections)

It is a Suburban Furnace

Any help will be appreciated.

[Guapotims]

Bump?

[h20ski]

I would love to have av answer for you, but I don't. Your problem still sounds like a loose conecton somewhere. It's a bummer troubleshooting an intermittent fault. Good luck!!!

[jimh]

the loose connection is what i think also.

have u tried moving the wires near the furnace with it running?

i would also suspect a sticking relay. could also have dirty contacts. (if it has one).

[AquaMan]

Does the furnace make any attempt to light before you smack it? ie: Does the ignitor make noise? After you have the furnace running, will it cycle on it's own, or does it need a gentle reminder (smack) each time?

[Guapotims]

I have wiggled the wires that connect to the furnace (with the thermostat turned on) to no avail. I don't think it is in the wiring. There must be a sticky switch or relay causing this. The sail switch works fine when the blower starts. It ignites the fire just fine. I believe I am going to have to take it out and start replacing parts (to avoid the hefty hourly wages of a dealer). I do appreciate all of your reply's and the time it took. . I will let you know when I get the problem resolved! Again, Thanks!

[Hal]

I'm no expert, but on the off chance this may help, have you checked for any corrosion or loos mounting of any of the electrical items, on the theory that it may be the ground connection which is the issue, rather than the wires? I suspect (don not know for sure, so be warned this is guesswork) that some of the electrical path may be conducted through metalwork/plates/screws, so you may want to check those as well.

For what it is worth, I had an intermittent issue with ours for a short time also, and found that the issue was the thermostat leveling - our had one screw that was loose and the unit would slide around a bit - after fixing that, all has been fine.

Best of luck, and if you find out what it was, please post!

[TURBS]

maybe when you bang on the side you wake up the squirrels ?

loose solder joint ?
loose wire inside a terminal ?

About the only thing a guy can do is diagnose it when its not operating by probing wires to see if its an incoming power issue or an internal power issue within the circuits and relays .


TURBS

[garbonz]

It may be the control board. You can remove it and have it tested. Some rv shops will do it for free.

[RodeoGeorge]

I'm voting for a sticking High Limit Switch. THE most common failure on furnaces.

RodeoGeorge