Payne furnace 396GAW048125

[fixadryer]

happy thanksgiving! (of course)

18 year old Payne furnace has worked fine all these years.  All of a sudden - blowing cold, burners won't stay lit more than 4 seconds.  I have bought new and replaced the control board (ie ICM271C).  I have bought new and replaced the spark igniter (ie Carrier LH680512).  I have shorted LIM1 and LIM2. I have confirmed ground to the chasis.  I have replaced the batteries in the Honeywell thermostat.

Immediately after replacing the spark igniter, the burners came on for about a minute, but after that, we're back to 4 seconds, although the igniter now retains its red glow constantly when the thermostat is calling for heat.  Sometimes, it's 25 seconds blower with no flame, and 4 second blower with flame.  Other times, the blower shuts off, and flame on for four seconds.  Unfortunately, the house isn't heating up above 58 degrees. 

Any thoughts???

[dkpd1581]

If your unit has a combustion fan motor, use a manomenter to see that you are getting the correct pressures during pre purge and after ignition  to keep the proving switch closed. 

While you have the manometer out, check your inlet and outlet pressures to the gas valve while it is  trying to run.  I would use a jumper and send 24 VAC  straight to the gas valve  while the ignitor is glowing and force the valve to stay open  so that I can check the  pressures  on both halves of the gas valve while running.  This will prove that the valve itself is good also.  You may see that  you are not getting your 3.5 inches of WC (assuming you are using natural gas) for very long after ignition on the mainfold side.  You may see the higher pressure on the inlet side of the valve not staying at about 5 inches or more to provide adequate gas pressure and volume to the valve.

Bleed the gas line one good time and remove any and all air that will have accumulated.  That will give you a chance to see if your gas regulating valve is opening (provided you have one).

Be sure to check the obvious before you start all of this....make sure the gas meter is not pinned and is on.  You would not believe how many people I have to give a $100 service ticket to after going out on their no heat calls only to tell them the meter is off.  The residual gas left in the lines is enough to cause the same type of problems you are seeing.

These are most of the mechanical things I would check.  The only remaining things I would look for is along the 24 VAC lines.  Make sure you are getting at least 24 VAC and that you are not bleeding voltage off somewhere due to defective connections, wiring, or improper VA rating on the transformer.

1*

[Brew Man]

Hey,

Flame sensor?

[fixadryer]

ok, well, I thought I'd circle back and let everyone know what it was, as I called a service tech in, who checked the inductance around the wires during the various light sequences

he replaced what he called the "ignition key", although, it looks to me like it's the main gas valve, he said the solinoid had gone bad after 18 years of cycling on and off, his repair fixed my initial problem

but created a new problem, BOOM!  when the furnace came on with the burners cold, sometimes a yellow flame extending out several inches from the furnace - not good

I then had the furnace serviced, which it hasn't been done in the 13 years I've owned the house, and after all the rust and debris was cleaned out of the burners, the furnace now works beautifully