Temperamental furnace

Glenn Harrison

If it was an 80MGF or G24 series with serial numbers of 6393, 6394, or 6395 in the first four digits, there was a service bulletin from Lennox in reguards to the paint flaking off the inducer housing which would slow down the air flow and cause the pressure switch to drop out. This flaking paint could also get in the pressure switch and cause it to malfunction. The fix was to put in a combo pressure switch and inducer motor kit.

Another thing to watch out for is the pressure switch port on the inducer housing plugging up due to corrosion. This also could cause the symptoms you described. Sometimes you can just clean out the port with a small drill bit and it will work fine.

Glenn Harrison Residential Service Tech

Althoff Industries Inc. Mechanical and Electrical Contractors

Crystal Lake, Illinois

Jim_9

I have a Lennox furnace model number G23Q2/3-75. When I came home from work on Friday the combustion fan was running, but the burner and main fan were not. When I lowered the thermostat and then raised it again it started up as normal. Unfortunately, the next time it started up the combustion fan ran, but they burner did not fire. Then the combustion fan will just keep running with the LED blinking indicated restart mode. Other times the unit starts normally. Any suggestions as to what is making my unit so temperamental.

Thanks,

Jim

Glenn Harrison

I can tell you exactly what is wrong with it

I work for a now former Lennox dealer.You should have a blue colored Johnson Controls Igniton module in your furnace.We are seeing an increase in failures in these modules due to connections coming loose on the module board. Sometimes the connections for the power lines will come loose so the module never attempts to fire the burners. Other times the connection comes loose at the spark wire, so the module energizes the burner but you don't always get a spark, which is most likely what you are experiencing. You need an igniton module conversion kit to resolve this problem.

Call your heating contractor or if you don't currently have one, click on "Find a Contractor" at the top of thepage, or if your anywhere near Chicago, let me know.

Glenn Harrison Residential Service Tech

Althoff Industries Inc. Mechanical and Electrical Contractors

Crystal Lake, Illinois

Unknown

Glenn is that a Johnson

G779 series control? Do you know the exact number? Also is it possible that the pressure switch could be involved? I guess because the code says it is attempting igntion maybe not.

Glenn Harrison

Timmie, that would be G776 series

Johnson numbers:G776RDG-1, G776RDG-2, G776RDG-10, G776RGD-11. Lennox numbers 74H26, 69J36, 41K87, 63K24 Respectively.


The first three modules have had service bulletins due to problems with them. I'm not sure if the fourth has been officially recognized as a problem by Lennox, as we have not been a Lennox dealer for three years, so we don't get service bulletins unless we ask for them. All of these modules have been changed because they would go into hard lockout for no reasons. The last two modules you could you could literaly wiggle the TH wire at the module and make the green light go on and off indicating a loss of power thru the module. On the 63K24 we are also seeing the spark generator having a loose connection where the module won't spark but if you carefully wiggle the spark wire you can make the spark start and stop. It took Lennox and Johnson controls 4 tries before Lennox finally gave up and went to Honeywell.

The new kit is a 53L90 which has a Honeywell S8660 spark module, and a new sensor, sensor wire, ground wire, and misc connectors. This kit will also replace Robertshaw modules 735 & 745 series modules used by Lennox. We go thru these modules like a hot knife thru butter. In this case the fact that the light is flashing tells me that it is going into 60 minute watchguard due to it not igniting the pilot. Now I will admit that there is the possibility that something else is wrong, but I doubt it due to the fact that it does work some of the time.


Glenn Harrison Residential Service Tech

Althoff Industries Inc. Mechanical and Electrical Contractors

Crystal Lake, Illinois

Arthur

Lennox Gas Furnace

I had a similar problem down here in our last winter (Southern hemesphere) The combustion fan would come on and then she would fire up and last about 10-30 sec and then go out again and then recycle again and again, Client complained of no heat as the furnace never got hot enough to run the fan. Turned out to be the combustion fan,The fan switch would close and when she would fire up then (or just after) the switch would open again. Took a pressure test with my digtial meter and found the old fan only had a 1/5 of the pressure that a new fan gave when fitted yet it seem to run OK and seemed to be able to get up to speed. Wanted the local agent to test and find out why (more out of curiosity than anthing) but they were only interested in selling new parts