# Any HVAC ppl on the forum?



## Riceburner (Mar 14, 2008)

Any HVAC ppl on the forum?

Got a Lennox G26Q3-75-2 that doesn't ignite after the first couple of times after a power stop/start. Goes to the "Control Retry period", then locks out and starts the retry period. Combustion Air Blower keeps running till full shutdown.

Tried bypassing the limit controller(that was replaced last year) and that doesn't seem to be at issue. Powered off the whole system, reconnected the limit controller and turned it on after a half hour. The ignition control LED stayed on when powered on and it worked. Seemed to be alright the few cycles, but but then it wasn't.

I powered off everything and cleaned the flame sensor with steel wool. Thought it might be the Johnson ignition control module G776RGD-11? 








I'm reading it may be the possible cause. http://www.hvacmechanic.com/forums/hvacr/messages/10227.htm

The pattern is, it works after a power down, but at the next call for heat, the Combustion Air Blower starts and just stays on. If I jumper the Differential (combustion air) Pressure Switch the main Blower kicks in, but no flame ignition. All lines from the pressure switch were clear.

I've moved on to checking the Rollout Switch. Metering it out, seems to be ok....reading 26+V from each terminal to ground. So if the Rollout Switch is good, might be an issue with flame/temp roll back. BUT...I had set it at a higher temp and it ran for a longish time....would think if a flame roll back was the issue it should have cut off. Will confirm/test again. Hope it's not the heat exchanger. The flue seems to be clear. There was good pressure from both the exhaust and intake pipes. PVC lines out the side of the house. Did notice quite a bit of water in the condensation line at the bottom of the Combustion blower though....I had just adjusted it to angle a bit lower...about 1/8".

The control board doesn't look like a Surelight or a BasicSurelight one either...so doesn't have any diagnostic LEDs.


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## Calmer (Mar 9, 2008)

Have you read this yet? http://www.hvacmechanic.com/forums/resservice/messages/27053.htm
Especially the last entry at the bottom that blames the johnson control ignition control unit. It's not the same ignition control model as yours but the details stated at the top seems similar. Hopefully you get a simple and not too expensive cure to this frustrating problem.


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## Riceburner (Mar 14, 2008)

yeah, seems the choice is the Honeywell S8610U 1003

An hour after the last cycle it worked. Will see if it's still going in the morning.


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## Riceburner (Mar 14, 2008)

Seemed to work overnight, but mid morning stopped.

last night I checked the flue and drains and all seemed to be ok. Adjusted the drain out of the bottom of the Combustion Blower...it was angled up a bit up. Some water did come out.

Now it keeps sparking when it's already on and shuts the gas off and on. Tried bypassing the Rollout switch and it did the same thing. Gonna try cleaning the flame sensor rod again. The reading from the flame sensor wire is .5DC microamps manual says less than .7 is low....Minimum is 0.15


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## Calmer (Mar 9, 2008)

It's always a gamble. The service guy would try a replacement piece and if it didn't work he just puts it back in his truck. You and I would most likely have to pay a 15-20% re-stocking fee at a store. 
This looks to be a good trouble shooting site: http://www.arnoldservice.com/Troubleshooting_Heating_Problems.htm


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## Riceburner (Mar 14, 2008)

yeah. part of what you are paying for is them having parts and the diagnosis.

I scrubbed the flame sensor with steel wool and even the tip of the igniter. spark seems stronger. Will see how it goes overnight.


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## paulof (Dec 4, 2009)

most likely flame sensor, if not very expensive get an ignitor also. a hairline crack will give you intermittant flame failures, so small that the naked eye can't see

paulo


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