I have a 10 year old Bryant 395CAV furnace. It starts and runs fine... after the temp has gone up between 1-2 degrees, it shuts off with error code 34 (Ignition Proving Failure). If I wait a few minutes and then turn power off and then on, it will start and run fine and then will shut off again with error code 34.

What is strange in this case is the combination of the furnace running for a while and the error code 34 (Ignition Proving Failure). From what I've been told, most of the Ignition Proving Failure problems would cause the furnace to not run at all.


I have (or plumber) done the following and the problem persists:
Cleaned filter
Replaced thermostat
Cleaned flame sensor with steel wool
Replaced flame sensor
Tested the ignitor
Tested the gas valve
Tested the electrical wires with a voltmeter
Replaced the control board

Fyi all the burners light and run until code 34

Any idea what is going on here?

I would say you need a control board, but that has been changed? Was it the exact board or a universal? Next thing to check would be a pressure switch on the vent if equipped.

It was the exact board... not sure about a pressure switch on vent... I can check on that.

Try this: raise thermostat setpoint to demand heating, and wait for burners to ignite. Wiggle the wires connected to the gas control. If main burners drop out, the terminal block interface on the gas control is failing.

Thanks KC... tried this... nothing happened, the burners did not drop out.

Is there a green wire connected between the gas control & the gas manifold? It is usually found where the manifold is attached to the mounting bracket.