Central gas heat. Sequence is: (1) t-stat asks for heat, (2) exhaust blower kicks in and makes exhaust pressure switch (3) glow plugs fire (4) gas flow starts (5) flames, heat exchanger heats up (6) fan limit kicks in and heats house.This works fine ... sometimes. It's easy to find a broken component, harder to find a temperamental one. Where would you start?
if you have only 1 setting on your heater, its probably the heater switch on the dash. also flush out the cooling system and change the thermostat.
Start by eliminating components. First jumper out the t-stat. Take it out of the loop. See if the furnace acts up. Next the pressure switch, etc. etc. Sooner of later you will find the culprit. Pressure switches rarely go bad. And if the vent is partially blocked it could cause intermittent problems. Check the filter. That could cause random limit issues. May be a dirty flame sensor that turns off the burners. T-stat problems will turn off the exhaust blower. If the exhaust blower still runs and burners shut off, may be vent or sensor issues! God luck! Hope this helps!
