Originally Posted by ga traveler
Persistant wins the prize. There is a overtemp switch on the furnace burner can. If the burner can gets too hot, it closes the gas valve. When it cools down it opens the gas valve and the furnace relights. It can be a restricted vent. (usualy a rug over the vent) a restricted air intake, A restriction in the ducts, or a weak overtemp switch. I am not guessing at this, I went to school on these furnaces. (Not that this makes me smart, just informed.)
It's called 'limiting'.....operating on the High Temp Limit Switch which is installed on the Heat Exchanger
Restricted air flow....discharge side or return air side...heat exchanger gets too hot & high temp switch opens.
DC circuit is interrupted hence gas valve closes.
FAN continues to run.heat exchanger cools down, high temp switch closes and DC goes to circuit bd.
Because Thermostat is still calling for heat the circuit bd energizes gas valve/ignitor.
Furnace refires....repeat the 'limiting' cycle until room air temp reaches thermostat set point---if it can.
Airflow is being obstructed.
Check for any items stored that would block return air to furnace and airflow from ALL ducts
Furnace (Burner/fan) should only shut down when thermostat opens because set point temp has been reachedl
Any other way and something is not functioning corretly
Excessive 'limiting' operation can cause therm stress to heat exchanger which can cause it to crack.
Cracked (even warped) heat exchanger will allow CO to leak inside RV.....dangerous situation.
Find the reason your furnace is 'limiting'