Our 8MPT died in the middle of the night about 10 days ago after 4 1/2 years of operation. We called in our local hvac contractor who observed that the furnace was firing in the pre-heat cycle at hi inductor motor speed and when the unit was shifting to low speed operation the burners would die and the main fan would kick in but the inductor motor would not run at low speed.
The indicator lamp on the gas valve read 8 blinks - limit control or pressure sensor failure.
At this point the contractor has changed all the main components - control board, pressure sensors, limit switch, gas valve, and inductor motor. The chimney appears to be clear as it is capped and a gas water heater is run out the same flue. Nothing has changed the initial symptoms and the contractor is stymied.
Any information that I can pass on to help with this problem would be much