Industrial Heater Troubleshooting

[CAMAN]

I've got a large Lennox commercial size heater in my building that has been acting up. It runs fine when you first start it up, but when it comes to temp and shuts down it won't start back up unless you power it down and back on. The exhaust fan comes on and I can hear the gas valve solenoid click, but it won't even attempt to start or spark.

I've cleaned all the sensors I can find and checked all the electrical connections. Anything else to check or with the symptoms, an idea of what needs to be replaced?

If it matters, it's a model number LF24-300S-1 manufactured in 1994.

Thanks a ton in advance!

[jeffreyd]

doing a quick search yields that they have a new ignition circuit board out that took care of many issues. also the on the old board there may be a diagnostics light that will blink out codes like a check engine on a car does. just from my quick reading i would lean toward the new board.

[pureinsanity]

My friend had an issue similar with his Modine. He ended up playing around with a tester and made a big spark and it tripped the breaker and when he turned the breaker back on it was fine.

Have you tried resetting the breaker? Im assuming by powering down you are just using a light switch?

Not sure if this will help but sometimes things like this just work???

[CAMAN]

Thanks guys, I'll check into the circuit board, don't really know if we want to spend $400 on one right now though. Ouch! I'll also try flipping the breaker and cross my fingers and hope that's it, I would be extremely relieved if it were. Anybody else have any input on this?

[pikechaser]

probly better off calling in a heating guy..flippin the breaker is not gonna fix anything..could be bad board..poor electrical connection..poor ground..pretty much all control boards require a good ground to operate/sense flame properly. throwing parts at it may not fix it either.

[Surface Tension]

You have a self diagnosed circuit board with led readout.

To interpret that code there will be a sheet on the door panel or in your owners manual.

That won't always tell you the exact problem but it will tell you where the sequence is hanging up.

For example if it is something to do with the induction motor it could be a bad switch, leaking hose, rotted hose, crud in the hose or fitting, and so on.

Turning the power off to the furnace resets the faults so the starting sequence can start again.

Anyway get the code and go from there.

[CAMAN]

ST, this unit doesn't have a diagnostics on it unfortunately. With the recommendation on checking the ignition circuit board I pulled it just to see what it looked like and one area of it looked as if it had overheated and part of the circuitry had burnt up. I did a quick repair to it and it's working again. We ordered a new board ($150) and will install it when it arrives. Thanks for all the help, hopefully this will give a permanent fix. If it doesn't last we will be calling in a pro.