Lennox G23 heater randomly turns on and won't turn off

kgold · 05-20-2012, 04:55 AM

I have a Lennox G23 furnace from 1994. About a week ago, in the middle of the night, I had the entire system turned off manually at the thermostate, but woke up to the heater going full blast, flame and all. System was still "off" at the tstat. The only way I could get it to stop was to unplug the unit. I plugged it in about 12 hours later, and it was fine another 24 hours, until the heater came on again while the AC was running. I've replaced the thermostat, BCC board, and have a brand new filter, but just experienced the exact same problem again. Any ideas?

**beenthere** · 05-20-2012, 06:05 AM

Intermittent short short in he thermostat wires.

biggles · 05-20-2012, 07:03 AM

with it running with no call...remove the stat off the subbase....still runs? remove the W1/W2 wires off the subbase...? go down to the furnace and remove W1/W2 off circuit board..shuts off

the stat wires R to W are touching calling for heat

between the stat and furnace

kgold · 05-20-2012, 10:23 AM

I have a Okfulemaster dual fuel control board mounted to the bottom of the BCC box. Could that be bad and causing the problem?

**beenthere** · 05-20-2012, 12:30 PM

Yes, that could be the cause of your troubles.

kgold · 05-20-2012, 05:41 PM

After checking the wires, I'm really leaning to the Okfuelmaster being the issue. When I disconnect the thermostat entirely from it, it is still calling for heat. Would 16J92 Fuel Master FM21 be the correct replacement part? If so, it looks like the wiring is labeled completely differently. Do you have a resource that can translate the old wiring labels to the new?

**beenthere** · 05-20-2012, 06:07 PM

No I don't.

05-20-2012, 04:55 AM	#1
kgold Newbie Join Date: May 2012 Posts: 3	Lennox G23 heater randomly turns on and won't turn off I have a Lennox G23 furnace from 1994. About a week ago, in the middle of the night, I had the entire system turned off manually at the thermostate, but woke up to the heater going full blast, flame and all. System was still "off" at the tstat. The only way I could get it to stop was to unplug the unit. I plugged it in about 12 hours later, and it was fine another 24 hours, until the heater came on again while the AC was running. I've replaced the thermostat, BCC board, and have a brand new filter, but just experienced the exact same problem again. Any ideas?

05-20-2012, 06:05 AM	#2
beenthere An old Tradesmen Join Date: Oct 2008 Location: PA Posts: 19,045	Lennox G23 heater randomly turns on and won't turn off Intermittent short short in he thermostat wires.

05-20-2012, 07:03 AM	#3
biggles Member Join Date: Jan 2008 Location: Long Island Posts: 3,250	Lennox G23 heater randomly turns on and won't turn off with it running with no call...remove the stat off the subbase....still runs? remove the W1/W2 wires off the subbase...? go down to the furnace and remove W1/W2 off circuit board..shuts off the stat wires R to W are touching calling for heat between the stat and furnace

05-20-2012, 10:23 AM	#4
kgold Newbie Join Date: May 2012 Posts: 3	Lennox G23 heater randomly turns on and won't turn off I have a Okfulemaster dual fuel control board mounted to the bottom of the BCC box. Could that be bad and causing the problem?

05-20-2012, 12:30 PM	#5
beenthere An old Tradesmen Join Date: Oct 2008 Location: PA Posts: 19,045	Lennox G23 heater randomly turns on and won't turn off Yes, that could be the cause of your troubles.

Lennox G23 heater randomly turns on and won't turn off