strange Warm air furnace issue

tbart16

I have a ADP brand, model SEP175-A warm air LP furnace. Thermostat calls for heat unit cycles as it should lights up everything is great , burners heat, fan runs i have heat , Hooray! BUT then the fun begins. the unit will operate properly for approximately 5 cycles maybe 7 minutes, at this point the fan keeps running until the furnace is cool but the unit will not relight. So if I cycle the thermostat from 50 to 90 unit will light, If I switch thermostat from heat to off and back to heat unit lights. If I disconnect the limit switch and reconnect the unit lights. The main control board was just replaced, the old board would not send power to the exhaust fan. Any help appreciated thanks Tom

STEVEusaPA

"...If I disconnect the limit switch and reconnect the unit lights..."
I think your limit switch is sticking. Also, is everything properly grounded?

ratio

Do you get an error code flashing on an LED or anything?

Also, what does "approximately 5 cycles maybe 7 minutes" mean? 5± cycles of about 7 minutes firing each before you have trouble again?

JUGHNE

Lack of air flow...filters or ductwork.
I had one do this cycle on limit constantly because of lack of ductwork.
It was never noticed until the limit switch got tired enough to not reset. If you pull the wire off of the limit, that physical motion/disturbance might reset the limit and you are off to heating again.

Between lack of duct and installing better air filters which cut down on air flow the limit would open. The hair that did the camel in was simply going to higher rated/better filters. He is back to the cheapies again.

tbart16

LED error code "system lockout fail to detect or sustain flame". Sorry that should have been in the original post. Unit is hanging in my garage no duct work. 5 cycles lasts about 7 min. A cycle being exhaust fan starts, burner lights ,blower starts, burner shuts off. It will cycle 5 times then needs to be "reset" Hope that makes sense. I will check the ground ,it should be good but you never know. Thanks again everyone.

ratio

Buff the flame rod with a dollar bill.

John Mills_5

ADP doesn't make furnaces, that's a unit heater.

MilanD

Flame sensor.

tbart16

I will buff the flame rod tonight, thanks. John Mills I stand corrected your comment WAS extremely helpful and appreciated

tbart16

Flame sensing rod buffed with a dollar bill all is well furnace runs like a champ thanks

ratio

Thanks for the follow-up!

nicholas bonham-carter

I hear the $20 dollar bills may have more "abrasive" on them!--NBC