Thermocouple

[_knight_]

I've got a reznor heater that the pilot wont stay lit, there are 3 of the same heaters. Other than the thermocouple, what would hold the pilot out from staying lit?

[bigjohn79]

Its got to be a bad solinoid in the gas valve. There are ways to test it but it is a safe bet to just change it out.

[jayguy]

make sure the pilot is in the right position and getting proper flame. will it light at all? not even light up? light but not hold when gas valve opens?

[_knight_]

It's the one where you hold down the button on the gas valve for 1 or more minutes until the thermocouple gets hot enough, or gives a 30 millivolt output. but there are two red wires that go onto terminals coming out of the gas valve, these terminals are directly connected to the thermocouple, but go to a thin like [=====] limit thats inside the heat exchanger compartment. The problem is, that the heaters are so high in the air (30+ feet) that I can barely reach the gas valve and thermocouple assembly, so I'm wondering what these wires go to, or if it's just some sort of limit switch that cuts out the pilot once it gets hot enough in the heat exchanger. thanks

[jayguy]

i know some units have a manual reset limit in the upper portion of the heat exchanger. it trips when the combustion motor does not move enough air (kinda like flame roll out). i thought that this went to the gas valve though, not the pilot. i could be easily wrong though.

[just_opinion]

Pilot light goes out - Not only the thermocouple and the gas valve are the problems. But the environment is the major factor. For instance if they are in the car collision repair wahrehouse. The building is in negative pressure (alot negative) whehn they close all garage doors. Thus the air draft back down from the vent pipe and blows out the pilot light. So pay attention to that.

[hands]

If the pilot light is going out right after you let off of the gas valve button, it is most likely the thermocouple, I assume you haven’t changed it already. You should rent a lift to do the heating check-outs on all three of the Unit Heaters if they are 30+ feet high. You should change the thermocouples on all of them as this is part of heating maintenance. If the pilot is staying lit for awhile and going out randomly, it could be a hole in the heat exchanger or negative building pressure as mentioned before.

[t527ed]

gonna have to get up high enough to check the limit that is hooked to the red wires. if that is open pilot will not stay lit. if closed it is thermocouple or gas valve.

[lirunaway]

If you do change the thermocouple the package may have a warning not to use sealant. Like most warnings they don't continue to explain why, so we ignore them. I always try to do a quality job therefore found out the hard way. The sealant will interupt the signal.

[service guru mike spisak]

could have dirt and debris up in the pilot orrifice
you know that white stuff

[trane]

Those red wires go to what is called a ECO limit that can range from 150 to 200 degrees depending on model and size.
It could be doing its job and nothing is wrong with the pilot or thermocouple.

[bigjohn79]

Just curious if the building is under a negative pressure don't you need some kind of forced draft system anyway to keep the CO out and if you do don't you need a Direct Spark Ignition or a Hot Surface Ignition???

[indian]

I could fix it for you, all you would need to do is pay the bill.