Keeprite 80+ 8MPT troubleshooting problem

[gomaster]

Hi,

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
appreciated.

Thanks,
B. Friedman

[beenthere]

Ask him to check with a manometer.

If he doesn't know what to check with it, you got the wrong contractor.
Have him call tech support.

Sorry, this is not a DIY site. So we are not allowed to give out DIY advise.

Please read Site Rules Thank you.

[gomaster]

This is not a DIY question. The contractor has been in touch with techsupport for days and they haven't been able to give any advice other than changing components. I'll pass along the manometer tip, but if there is anything else you can add to this please let me know. BTW this was the contractor that originally installed the furnace.

[beenthere]

Anything I could add, would be DIY info. As far as it would be instructions that a DIYer could follow.

Have him get tech support to come out to your house.

It is part of the job of tech support. In cases like his.