This is regarding a 12 year old HEIL 7000 furnace.

When the house thermostat calls for heat, the induction exhaust fan kicks in and in a few seconds the pilot and burners are activated (all appear normal).

Prior to the activation of the circulating fan, however, the high temp switch appears to trip, the burners shut down (exhaust fan continues to run), and THEN the cirulating fan starts... The pilot light and burners then restarte and everything appears fine. Shut down appears normal when house thermostat reaches temperature setting.

The next time the thermostat calls for heat, the same routine occurs.

My induction exhaust fan had been very chirpy and noisy so I just replaced it - this is when I noticed the above sequence of operation...

Suggestions??

It is not sensing the pilot flame. See posts or sticky about flame sensors.

I did another operational test:

From the house thermostat control, I put the circulating fan to "Always On" and then set it to call for heat. In this scenario, everything operates as expected and the high temp limit switch does not trip... If there was a faulty pilot sensor, I would expect it to shut down as before...

I noticed that their appears to be a Blower Switch with adjustable timers on it.

HEATCRAFT
Model FTC5-EH01
HQ1005229HC

Would a failure of this component produce my symptoms? Adjustments?

Thanks for your help.

Bad heat fan relay on the board I bet.