Furnace Trane XL 80 does not fire up

theoj

HI,
I am having an Trane XL 80 (TUD080R936K0) furnace which has problems starting up. The gas never starts flowing when the heating element is red hot.

Detailed Current Observations/Symptoms

1. The furnace yet request for heat.
   
2. The controller correctly signals the request
   
3. Switch click -> The Furnace Draft Inducer Motor starts running.
   
4. Switch click -> The Heating Element is warming up and is reaching to glowing state.
   
5. Switch click -> Normally now the gas would start flowing but nothing happens.
   
6. Switch click after about a second -> The heating element is turning off.
   
7. The Furnace draft motor runs for 1-2 mins and turns off.
   
8. Repeat of previous steps.
   

History of previous issues and replaced parts

1. Nov 2016 - Control board fails and also startup issues. Replaced parts: Control Board, Flame Sensor
   
2. Dec 2016 - Still startup recurring start up issues (draft motor starts, heating element starts up, gas flow starts but turns off after 1-2 seconds). Replaced parts: Flame Rollout Limit Switch, Pressure Switch, Draft Inducer Motor, Tube [to pressure switch]
   
3. Oct 2017 - Startup issues again. Again heating (draft motor starts, heating element starts up, gas flow starts but turns off after 1-2 seconds). Replaced parts: Flame Rollout Limit Switch
   
4. Oct 2018 - Startup issues again. Again heating (draft motor starts, heating element starts up, gas flow starts but turns off after 1-2 seconds). Furnace starts working after troubleshooting session and cleaning.
   

Previous observations

1. For the previous symptom (draft motor starts, heating element starts up, gas flow starts but turns off after 1-2 seconds) it often was turn out that opening the cover while troubleshooting the furnace for some reason made a difference and the furnace turned off, while with closed cover it did not. This was not always the case but a few time. After running it for some time (supervised) open, the furnace had no issues turning on again for a full season. Does that make sense to anyone?
   

ratio

Check for power to the gas valve, the terminals should see 24 VAC after the ignitor is hot. Watch carefully, it sounds like the controls only give it 2 second to prove ignition. If the power's there, check the gas valve itself, also make sure the gas is on to the unit.
BTW, most of your other startup troubles sound like proof-of-ignition related, either flame rod dirty or out of position, or burner grounding.

Tim McElwain

It sounds like you may have a problem with ground long term. Find the bare copper wire in your 120 volt feed to the boiler and run a 18 gauge wire from it to the gas valve. Attach it to the body of the valve (some valves actually have a clip on the valve for that purpose).

unclejohn

Make sure the gas is on. There may also be a on off switch on the valve its self.

theoj

Hi all,
Thanks for all your feedback. The root cause for the issue was a defect gas valve which needed to be replaced.

I will look into the burner grounding but so far so good.

Thanks again!