DIY Chatroom Home Improvement Forum

DIY Chatroom Home Improvement Forum (
-   HVAC (
-   -   Lennox Furnace problems (

boolean 12-18-2008 10:37 AM

Lennox Furnace problems
its a furnace from '97 with a honeywell thermostat bought in 05

no problems until last weekend, when it failed to start heating even when the thermostat has the "heating" display showing. The furnace does start after switching the master switch off/on, then it would heat the home normally for the rest of the day until the morning, im guessing its not starting after a long time of inactivity because I set the period between 12am - 9am to 16C instead of the regular 18C during day time.

I took out the flame sensor yesterday to scrub it clean with sand paper by advice from the net/inspector who couldnt find anything wrong with the furnace since it was working when he came. But it was cold again when i woke up this morning, down to 14C when the thermostat is set to 18C.

anyone know what the problem might be?

SKIP4661 12-18-2008 01:46 PM

Does this furnace have a blue Johnson Control ignition module? This is a box approximately 7" x 3.5", give or take mounted to the firewall. Replaced tons of these controls for the exact problem you have stated. They have bad solder connections on the module board.
If you replace this module replace it with the Honeywell kit. Do not use the Johnson replacement or it will fail again.

boolean 12-18-2008 01:56 PM

hey what do you know, it is a johnson ignition controller

G776RGD-11 is the model/serial

you think that's the problem? how do I make sure?

SKIP4661 12-18-2008 02:10 PM

I would just about guarantee that module is the problem. Next time it fails look at the module and see if the green light is on. If the light is on the module is bad.
I am also assuming the furnace is a G20 or G26.

boolean 12-18-2008 02:14 PM

so next time (probably tomorrow morning) the house goes cold, if the module's got the green light on, its busted?

SKIP4661 12-18-2008 02:26 PM

If it is the module and you have a G26 90% efficient furnace you will want to replace it with the lennox/honeywell control. If you have a G20 Whisperheat furnace you can use a universal module because you won't need the prepurge feature of the lennox module.

boolean 12-18-2008 02:29 PM

its a whisperheat, i'll keep that in mind tomorrow, thanks!

boolean 12-19-2008 09:40 AM

alright so the light wasn't on when this morning when it didnt start, does that mean the module is fine?

edit: now the heater wont even heat continuously after power off/on anymore, it just turns on and heats for like 20 minutes or even less, and shut off again

SKIP4661 12-19-2008 02:17 PM

I have seen those modules fail with or without light being on. The light is a sure indication of a failed module. You should replace that module.

boolean 12-23-2008 11:05 AM

I replaced the module with a Lennox Honeywell 30w33, all is well now

thanks skip!

chrisbatto 12-28-2008 08:30 PM

Replacing the module in the G20
Hi Booleen ....Guys,

I am assuming that you received a flame sensor with the 30W33 kit.

If you replaced the flame sensor, can you give me any tips as to the order of operations or what precautions you would take..

I am purchasing the kit tomorrow for the same intermittent problems



yuri 12-28-2008 08:43 PM

Follow the Lennox instructions and wiring diagram with it VERY carefully. I have replaced lots of them and am a Lennox tech. I would replace the pilot burner also. They warp with old age/get corroded and may be 1/2 the problem. Try for Lennox parts. Give them the entire model # and serial # as there are 2 versions of that pilot burner.

mfellows 12-29-2008 06:03 AM

I had the same issue with the Johnson Controller last week (in a G26 installed in 1995), the HVAC tech replaced it with a Johnson G776RGD-11 which I think is a used component and I am having the same issues again - can someone confirm that the G776RGD-11 is even manufactured anymore?

chrisbatto 01-12-2009 09:12 AM

New Control Module and Flame Sensor Works Great
Hi All,

My Dad and I have the same G20 Whisper heat furnaces Both 15 yrs old.

His was really bad, failing to operate 2-3 times daily between Christmas and New Year. We had to turn off the power and restart again otherwise the fan would just run continuously with cold air.

Mine had worked with just a clean up of the flame sensor area last year (brass brush and steel wool) but it had still acted up once since then.

You can't rest at night with these things going on.

I replaced the Module with the Honeywell replacement ( From Amre Supply here in Canada). And a Flame Sensor too. (About $210 total)

I replaced both parts on my Dad' working like a Swiss clock and igniting very quickly.

To have peace of mind, I did mine too.

I would recommend this to anyone who has an older G20 furnace. My reviews of many websites tells me this is going to be a problem if it hasn't started already.

Yuri and Skip are right and thanks to you. as stated.... MAKE SURE you read the instructions very carefully and completely a few times before you start.... and then read again during the job.... If you don't... you will be in serious trouble.

To replace the flame sensor
, you need to remove the cover panel above the damper flap (two small bolt) and you will need to disconnect the small aluminum? gas line from ahead of the Gas valve. I used a Brake line wrench to get even torque. (Shut of the gas at the valve!)

Then the two small bolts hold the whole thing onto a bracket inside the furnace. So remove these and fish the pipe out to replace the flame sensor in your lap or at a bench...just slides out and back in again.

Be careful of the wire routing and to not lose the grommets where the pipe and wires pass through the cover panel when you reassemble.

Test the gas fitting for leaks (twice if you are like me) by using soapy water and a kids paint brush.

Good luck


mlundquist 03-03-2009 10:26 PM

fan wire
I am replacing the lennox g26 johnson control 41k8701 with the honeywell 30e33 and am short one terminal. I have a wire that goes from the fan to the 4th spot on ground. Anyone have any thoughts on where that should go on the new controller? Do I have the wrong replacement part? thanks.

All times are GMT -5. The time now is 07:28 AM.

vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

Search Engine Friendly URLs by vBSEO 3.6.1