York P2MPD20L08001A "no heat, all fan" problem

[blue11]

> The only symptom I don't have is the restart after an hour, which perhaps my controller doesn't support.

I was incorrect about that.

The furnace does, in fact, reset itself after an hour lockout, and I get heat until the next time it loses flame 5 times in a cycle, when it locks me out again.

[Mr Bill]

blue11 -
.
> The furnace does, in fact, reset itself after an hour lockout, and I get heat until
> the next time it loses flame 5 times in a cycle, when it locks me out again.

Probably the inducer motor loosing vacuum to the pressure switch, maybe bad vacuum hose or loose, or could even be a bad pressure switch. If it was the flame sensor, the burner would shut down within 5 seconds of start, if it was a bad limit the fan only would run, no burner. Flame sensors hardly ever go bad, you can usually clean them with steel wool, also check your grounds, bad ground will cause the flame sensor to not operate correctly.

[heatseeker]

Limit switch, blower motor could be cutting out check amp draw and compare to motor. I its a 1 hp motor that should pull less than 12 amps.

[Freon]

Your description is very helpful even though inconclusive. It seems there is a flame sensing issue causing the retries but the question is, what is the real cause... dirty flame sensor or aging control board not sensing the current * And as you point out, the main blower continuously running is yet unexplained but could be a aging control board.

Can you see if the control board is close to the main burners and therefore subject to high * Heat kills electronics.

To rule out a thermostat issue, turn off the power to the furnace and disconnect the G wire at the White Rogers control. Then call for heat normally. If the blower still runs constantly after the heating cycle then I think your control board is the problem. Since it happens once every 10 times or so, you might see if you can remove it from the furnace case thereby giving it less heat exposure. You may buy some time.