York Diamond 80 Heater Blowing Cold Air

[RMN]

I have a York Diamond 80 heater blowing cold air. The unit is ~22 years old with no issues until now. Initial troubleshooting found the 120 Vac hot wire had pulled out of the wire nut and shorted to the metal case. I repaired that which allowed fans to come on but still no hot air. Thermostat seems to work ok with heater (turning on aux fan) and fan control (which turns on main fan but no heat). Pretty sure gas is working at least to the heater unit since kitchen cooktop burners work fine and I smelled slight gas during one trip to the attic near the furnace. Glow bar turns on and smaller fan comes on but no gas burners and then the glow bar turns back off after ~30 seconds or so. Tried resetting all 3 rollout switches and tried turning gas valve off and then back on. But still no hot air. Gas valve is getting ~28 Vac while glow bar is on but then turns off when glow bar goes off. Measured the resistance across the input to the gas valve and it reads open. So I assume this means the gas valve solenoid is dead. I checked control board diagnostic LED and it goes red when the unit first turns on but is not lit at all after that (no blinking codes). Can just the solenoid be replaced or does the entire gas valve need to be replaced? Anything else I should try before purchasing a gas valve? Thanks for your help.

[16345Ed]

I know next to nothing about furnaces. But sounds like classic ignitor failure. 

Edited December 15, 2018 by 16345Ed

[spencertech]

check for 24v to gas valve after igniter warm up but it seems like you have to replace the gas valve

[RMN]

Thanks for the suggestions. Ignitor seems to work since glow bar gets red hot but nothing ignites so I'm assuming that the gas valve is the cause. It has ~24V across it while the glow bar is on but that then goes away after nothing ignites. I also measured an open resistance across the gas valve solenoid so I assume that also means it is bad. Just wanted to make sure that was it and I wasn't missing checking something else before I bought a replacement.

[16345Ed]

I missed part about no resistance on valve. 

 

However ignitors can and do fail yet still glow. 

Edited December 16, 2018 by 16345Ed

[Gags730]

Check for 24 Volts at the Valve. 

If you have the voltage at the valve then Kill the power, and you need to check for continuity across the valve.  With the wires pulled  off the valve,  You should have continuity.  If not replace the valve.