Troubleshooting Pilot on Older Reznor

[iced98lx]

I've recently gotten the Reznor XL-75 unit heater that was previously in the garage in our new home hung back up, plumbed back in and fired up. I can get the pilot to light and hold but as soon as the system calls for heat it dies out. A little manual assist via propane torch and it lights up and runs perfectly. If it cycles off for any amount of time it then of course will not keep the pilot lit when calling for heat.

Seems like a classic "Replace the thermocouple" situation based on what I know (limited). There is an older used thermocouple hanging next to the heater but I assume if I match the length and connections any of these $5-10 options at Menards are going to function OK?

Am I missing anything on what it might be?

PXL_20201117_194347016 by Christopher Uthe, on Flickr

Sure wish I could get my hands on an electric ignition conversion kit, heater seems to be in great shape other than the thermocouple issue and heated up the space really nicely while being very quiet.

 

[nadogail]

If it is not the Theromcouple, start shopping for a millivolt operated gas valve.

 

[SALIV8]

The gas valve will have an adjustment screw on it to adjust the pilot.

It may have a cap that needs to be removed.

 

[samss]

Check your pilot light flame.
The first thing to check is the color of the flame. A natural gas flame should be a bright blue color with a small amount of yellow at the very tip. A propane flame will have more of a bluish-green flame with a tinge of yellow at the tip. The flame should be strong enough to cover about 1/2 inch at the end of the thermocouple tip.

If the flame is too strong and not adjusted correctly, it will be blue and may make a hissing sound as the flame crosses the thermocouple. The pilot should be adjusted to reduce the intensity of the flame.

A yellow flame is caused by lack of oxygen and incomplete combustion. If the pilot light is a weak yellow flame it will not get hot enough to heat the thermocouple to the temperature needed to enable the gas valve to open. This is often caused by a dirty pilot tube tip.

A split flame is usually caused by debris inside the pilot tube or the pilot orifice.

A flickering or wavering flame is usually caused by a draft. Check to see if there are sources of drafts in the room and take steps to reduce the effects on the furnace.

 

[naturalgas]

Pilot is dirty. Disconnect pilot line from valve.blow compressed air through line, reconnect and it should be fine.


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[fitter30]

Thermocouples lenght doesn't matter as long as its the same or longer. Check the gas valve side for tightest. They only put out 35mv. Where the pilot tube connects to the valve there might be a screw that when removed has a pilot flame adjustment.

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[iced98lx]

Thanks everyone for the suggestions, I'll clean out the pilot tube and try to adjust the pilot flame today and let everyone know how it goes!

 

[iced98lx]

The gas valve will have an adjustment screw on it to adjust the pilot.

Check your pilot light flame...

Pilot is dirty. Disconnect pilot line from valve.blow compressed air through line, reconnect and it should be fine.

Eureka. I disconnected pilot line, blew it out, re-connected, strong blue flame cycles just fine now. No need for a thermocouple!

Heater hasn't been ran for at least 2 years, if not 5+

Another win for the community