Gas and Oil Home Heating Furnaces - Lennox-burner Problems

I have a WhisperHeat Lennox furnace. My problem is, the furnace will go on, the pilot lite will ignite, then the blower will go on but the burner will not. Every once in a while it will work fine but mostly not. In October I had the flame seconsor and ignition control box replaced becasue the furnace would click numerous times and still not ignite. The furnace worked great up until a few weeks ago. Now I have this new problem. I have had a couple people (not techs) look at it and tested the volts and such and was told the correct amount of voltage /charge was registering. What else could be causing this to happen? I would rather not spend the money on a tech if it is something simple. Thanks for your time. Debbie

Some people do not realize that if they test with all the wires hooked up that a backfeed can fool them into thinking the low volt current is proceeding throuigh all the safety switches as it should be, when in fact it might NOT be.

I know first hand about this, and have proven this with leaving wires connected and not connected. And because of this I never leave anything like this to chance, whether working on furnaces, stoves, dryers, etc.

Some furnaces have low voltage wires go through the safeties and then go to the ignition control and then to the gas valve, but then a wire on the gas valve may go back to some starting point where there are a host of relay parts and this is where I speculate the backfeed is coming from; like back from there, then back into the gas valve from the other direction, then into the ignition module and then into the outgoing side of the pressure switch, etc.

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So what this means, basically, is your furnace may have to be diagnosed from scratch, all over again. After saying all of this, now I forgot what your problem was.

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Listen for any clicking at the gas valve or from in the ignition control module within say 15 seconds after the pilot lights. Then let us know if you hear anything. Pay close attention.

Did you replace the ignition module with another Johnson? If yes, your problem may be the module. They had problems with them. Of course check ground.

Agree with everyone else. If limits and wiring are good. I would suspect the control or the gas valve. A 24 volt test light is can in some cases be better (than a meter) for testing power at the gas valve. Since it appears the pilot valve is opening (pilot remains lit?), the main valve (mv to mv/pv) power needs to be checked.

And, just as important, check ground connections (especially at pilot assembly) as mbk3 mentioned.

If all else fails, get a technician. He/she can check with Lennox for any upgraded controls for this furnace. Lennox does provide good support for their equipment.

Just a safety note. The wisper heat has a duracurve heat exchanger and 90% of the time these are cracked. This would creat a very dangerous problem. I would have it checked by a pro. Its a small price to pay for your life.