[kdubendorf]

My Trane XV-90 is not heating on its own. When a thermostat calls for heat it goes through the following cycle:

Combustion Blower Starts
Igniter starts to glow
I hear a click
The igniter turns off after about 15 to 20 seconds
The Combustion Blower Stops
The Combustion Blower Starts
The Igniter begins to glow
I hear a click
The igniter stops glowing after about 15 to 20 seconds.
The Blower Fan comes on with cool air blowing throughout the house. No further attempts are made to ignite unless I reset the system.

I can get the unit to work by tapping with my hand on the bottom of the gas valve when I hear the click. At that point gas ignites, the igniter stops glowing and the furnace operates normally until the call for heat is satisfied.

The unit currently has 2 zones with a Trane Zone system. The model number is TUY100R9V4V1. It's about 10 years old and in good shape.

Three questions:

1. Is it most likely the gas valve? (I think it is since tapping on the valve causes the gas to ignite).

2. If it isn't the gas valve what else should I be looking at?

3. Any suggestions on where to purchase a 2 stage gas valve? The one location I saw had a valve that looked like it a different jack than my gas valve.

[KISS]

1. Yes

2. Voltage to gas valve. Voltage drop across relay controlling gas valve. These aren't likely. Other possibilites: transformer, relay activating gas valve, low gas pressure.

3. 2 Stage Gas Valve, 24 Volt Coil, 1/2" inlet 1/2" outlet.(White Rodgers) *UPGRADED MODEL: American HVAC Parts