Furnace flame won't stay lit

[redz1006]

I have a 3 yr old Comfortmaker Environplus 90 furnace used for heating and cooling. It suddenly developed a problem with the flame
not staying lit. When I reset the furnace, I did notice that the
automatic igniter will light the flame but the flame will only be lit for a few seconds after the system shuts it off again. It does this about 5 times more, then the system will stops trying. I believe this is part of the systems safety feature. I have new filters and airflow
is good. The fan is working fine when in "on" mode. Correct me if I'm wrong, but I think the next step on the cycle after lighting the flame is to turn on the fan/blower. This is not happening at all.

This is what I think could be wrong :

1)Igniter assembly is bad
2)Bad or dirty flame sensor
3)High switch not calibrated correctly (or stuck)
4)Gas valve control syste bad.

Any thoughts ?

I have to admit, aside from changing the filters and the aluminum
grates for the humidifier, I have done no preventive maintenance.

Also, the LED for the W wire is blinking in the Aprilaire zone controller mother board (I have dual zone) .
I know the the W wire in the thermostat controls the gas burner.
I believe the number of blinks mean something too. DO you know where
can I get information to interpret the blinks ?

Gotta ask first before calling it in.........Thanks in advance.

[Mike3]

# 2 sounds like a good place to start. Clean flame rod with steel wool and also clean pilot with compressed air if you have any. Maybe keyboard cleaner

[redz1006]

Thanks Mike but I got it working again by turning it off from the
main electronic switch board. Turning off the furnace using the
red switch on the side do not cut the power to the zone controller box. I guess this is just like rebooting your PC when it hangs. With that behind me, I'm now looking for a reputable company to do
preventive maintainance. Any recommendations ? What is the usual prices range for this service (heating, A/C and Boiler). ?

[HayZee518]

The flame detector is usually the culprit. If there is a cad cell replace it. If there's a flame rod clean it or replace it. Rarely does the lockout relay go, if it's shutting down the circuit it's working.

[jcohn]

Thanks so much for you input!
I cleaned my flame sensor with some fine sandpaper and WALLA, furnace works great again.

Thanks guys.