York Diamond

Sorry - hit wrong button. More detail.

York Diamond D 80 - 2 stage
RTH7500D Thermosat

Blowing cold air - no burner, main fan running, flash 7

Furnace works fine when first turned on. Heats house. Problem seems to occur after running awhile or when trying to restart?

Always have seen great ignition sequence. Small fan turns on, ignitor glows strongly, gas on, strong flame, after some seconds, more gas and main fan on.

Have to turn furnace power off to reset. Always restarts fine.

Cleaned flame sensor with steel wool. No difference.

Maybe bad flame sensor? I have recording DVM. What is the output range for the flame sensor?

Any other ideas?

Thx. Fraser Jim

Flame sensor failure is very rare. There should be a legend somewhere on the unit to describe what the LED is displaying.

I cannot find a ledgend, but a York manual for a similar furnace says that a Flash 7 means that "flame could not be established". "Could be low gas pressure, faulty gas valve, bad igniter, burner problem".

When I look at sequence, it normally starts fine, and exhibits no symptoms from above, so that is why I'm thinking sensor.

Fraser Jim