This Furnace is approx. 7 yrs. old.
The thermostat calls for heat. The furnace ignites,
runs for a short time, not reaching the set tempature,
Then the fire box shuts off and the plenum blower continues
to run seems to cool off the fire box, then the the fire box comes on and
runs for one minuite and still has not reached the thermostats pre-set
tempeture, then continues this cycle until it reaches the thermostat pre-set