Intermittent Lennox Gas Forced Air Furnace G12D2E-82-2

[mangusta1969]

I have an aged (1979) but lightly used 82K BTU Lennox natural gas forced air furnace (Model G12D2E-82-2) that has become an intermittent starter over the last 12 months.  Once started, it usually will run all night, cycling off and on, as the room thermostat calls for heat from the furnace.  Sometimes, it will just not spark reliably to start the small pilot light and the furnace will not come on.  This can usually (but not always) be cured temporarily by turning the room thermostat off for about two minutes and then back on.

It has a spark control unit with the Lennox part number 10B2301 and serial number 7906 on it.  This spark control unit also indicates a manufacturer of White Rodgers/Emerson Electric on it, with another designation:  Type 50A22-2.  This spark control unit uses an automotive type high tension wire on it that goes to a combination spark mechanism/thermocouple/pilot light.  When the spark unit works, it lights the pilot light, then the gas valve activates the main burners which ignite from the pilot light when the thermocouple has come up to temperature. 

Is there an on line source of parts for this old Lennox furnace? My local HVAC supplier in San Diego says the numbers I have are obsolete, but that he might be able to match some parts up if I remove parts from the furnace and bring them to his counter.

Has anyone had a similar intermittent ignition problem with an elderly Lennox furnace and solved it with a third party spark control module and/or sparker/thermocouple/pilot light assembly?  Just in case anyone needs it to assess my situation, the gas control valve is a Model 36C84 Type 216 unit.

[dkpd1581]

http://www.lennoxdavenet.net

You will have to make your own sign on and account....this should be free.  Lennox is VERY proprietary about their equipment.  You, generally speaking, cannot get generic parts and expect them to fit a Lennox unit - Lennox tweaks their parts so you must go to them almost exclusively.

http://www.white-rodgers.com

This site will help you find the current replacement for your out of date ignition system.

You would be better served to check the gap on the sparking unit and put it back into spec and gently clean the electrode and grounding metal surface.  This most likely will help your problem

[AccApp]

Looks like the replacement is a White-Rodgers 50A22-4. Should be readily available almost anywhere. The flame sensor on this relies on a good ground path from flame to module's ground. Clean what you can and give it a shot.

[mangusta1969]

DKPD and AccAppThanks for the links and the tips.  The Lennox site requires a master customer number to log in.  Maybe I can get that number with a phone call tomorrow.

The White Rodgers site indicates the 50A22-2 spark control module has been superceded by a 50A22-4 module, which looks about the same as the existing module on my G12 furnace.  At least I have a newer part number to search for now.

I did find quite a bit of information about the Lennox/White-Rodgers spark control module on a Bob Vila site today.  Many of the posters indicated that there were internal problems in some of these control modules due to corrosion and aging of poor solder joints.  The symptoms of the problem modules were just about identical to my system's symptoms over the last year.  Several posters said to be certain the modules were well grounded.  A couple of posters indicated that they resoldered all of the PC board connections and reliable operations began again.

I will take a look at the electrode and thermocouple, as you suggested.  In my searches today, I didn't see anything about the proper distances between the hot wire electrode and the ground shield, but suspect the spark gap should be around 1/8-1/4 inch or so.

[dkpd1581]

Page 2 of the 50A22-4 PDF states 3/32 to 5/35 of an inch for the clearance.  You can call around to some of your local parts houses and see if they have one in stock.  It is far easier and safer to just change the thing out rather than resolder things.

You have save the lion's share of a service call already, now its just down to the part.  With an exchanger that is 28 yoa, you might be better served to inspect it for cracks and CO.

Best of luck.

[dkpd1581]

Here is a copy of the White Rodgers PDF ... forgot to attach it to the previous message...sorry....its early here....

0037-5440rev_A.pdf

[mangusta1969]

DKPD,

Thanks for the great assistance.  I downloaded the manual just fine and will purchase one of these replacement -4 spark control modules, rather than attempt the resolder repair. 

Since the G12 furnace is located near San Diego and only about two miles back from the Pacific Ocean, it doesn't see too much use, even in the winter.  It probably only has the equivalent of about 4 years of heat cycles/duty hours on it, compared to an east coast or midwest furnace.  It has only gone below freezing here twice (for about two total hours) in the last 27 years.  The auto traffic in the San Diego area is another story, however...

Thanks again for your knowledgeable help.

Steve

[applianceman18007260692]

living that close to salt waterm can cause some of the terminals to get lousy connections

make sure you have a good burner ground

this will cause intermittant probs

[mangusta1969]

ApplianceMan,

Thanks for the tips.  I will try to attack my G12 problems this week and I will let everyone know what I find (flaky connections, bad spark unit, electrode mis-aligned, etc.). 

This is an awesome forum, with extremely knowledgeable people participating; they offer great and timely advice.  It's nice that everyone is treated with respect, too, so rookies like myself aren't afraid to ask basic questions.

Thanks,

Steve

[mangusta1969]

ApplianceMan,

Thanks for the tips.  I will try to attack my G12 problems this week and I will let everyone know what I find (flaky connections, bad spark unit, electrode mis-aligned, etc.). 

This is an awesome forum, with extremely knowledgeable people participating; they offer great and timely advice.  It's nice that everyone is treated with respect, too, so rookies like myself aren't afraid to ask basic questions.

Thanks,

Steve

[mangusta1969]

living that close to salt waterm can cause some of the terminals to get lousy connections

make sure you have a good burner ground

this will cause intermittant probs

Well I sold the SoCal house and its two Lennox furnaces back in 2007, without ever fixing the intermittent ignition problem. Since I just got the house back recently via a re-possession from a deadbeat owner, the problem is mine again.

Some of the ground comments on this forum and on another Lennox-only forum led me to just try running a separate ground wire between the spark ignitor/flame sensor thermocouple mount and the gas valve. Just doing this completely solved the intermittent ignition problem and has improved the spark ignition system to immediately light the furnace's pilot light, too. Apparently the main problem is that there was a low current flow from the flame sensor (located in the pilot flame) to the gas valve. This caused the gas valve to go into safety shutdown mode about 30% of the time when the main burners ignited; I guess the low flame sensor current flow situation was improved with the separate ground wire. I can see that the pilot flame is reduced significantly when the main burner ignites; perhaps this furnace was just operating on the raggedy edge for the last few years.

At any rate, the heat exchanger is still in good shape and the furnace works just fine again. Anyone want to buy a big two story custom house near the San Diego coastline with two fully operational 82,000 BTU Lennox gas furnaces in it? Thanks to all for their comments and advice.

[kdog]

Great follow - up ! makes perfect sense, years ago I had to often service those cheap retail BBQ's that had cheesy ignitor components that would fail because burner contacts to frame would corrode etc and when I had one that would haunt me I would install a ground wire directly to the burner with a screw and run it back to ground on the snap button device and they would work flawlessly thereafter. did that to my own and the repair outlived the burner.