Asked on Feb 17, 2013

We have a Weil-weyman hot water furnace and have had 3 thermal couplinks installed in 3 years. Is this a lot?

Woodbridge Environmental


This furnace has given us nothing but trouble. Had it fixed many many times. It is about 14 yrs. old and am ready to throw it out. We get a new part and then another part goes bad so he says.
1 answer
  • If the thermocouple is being changed out that often It can be one of two things that is the issue. 1. incorrect install or proper flame or 2, faulty gas valve. To understand what is going on you need to understand what the thermocouple does. Inside the tiny bulb that the flame is coming into contact with is two dissimilar metals. And connect to them is a wire. When the metal is heated it generates a very tiny voltage which is delivered to the gas valve. Inside the gas valve is a winding of wires that sees this millivolt current and the winding's amplify this current to create a magnet. This magnet in turn holds a tiny metal bar into place that keeps the gas valve in a position that allows the main flame to operate. Should the pilot light go out the voltage is loss thus the tiny metal bar is no longer held into position. This in turn prevents the main gas from coming on filling the boiler or furnace from filling with gas that is not lite from the flame. If the flame is not large enough and is not properly hitting the thermocouple in just the right spot it will not produce this millivolt current. If the thermocouple corrodes from rust or debris it also will not produce current, If the connection to the gas valve corrodes or comes loose where the wire connects to the gas valve, it will not transfer this voltage to the gas valve and it will not hold the rod in place and shut down. If the wiring within the gas valve is faulty or has failed, it may require the maximum amount of voltage only a new thermocouple can produce and not work as a result. My guess it is either a poor pilot, a poor connection where it connects to the gas valve or the gas valve is faulty. I have seen in the past where thermocouple fail, but three times? Not so much. If you determine that the thermocouple pilot light is bright blue with no yellow flame at all. Yellow indicates that the pilot light is not burning properly and the yellow will produce soot that prevents the thermocouple from working as it should. And that the bulb end of this device is clean and not dirty, then remove the wire out of the gas valve and very slightly sand it with very fine sandpaper or emery cloth. Just enough to make is shiny, no more. Put it back in the valve and try lighting the pilot again. If that does not work, then the gas valve is faulty and needs to be replaced. Even if works after putting in a new Thermocouple it will fail again. Sometimes the wiring within the gas valve corrodes just enough that it requires the current only a new thermocouple can provide, As they age they loose some of the ability to produce enough current to hold the gas valve pin into place and the result is what your experiencing. Lastly, My only question would be is, Does the pilot stay lit once you light it again? Or does it go out as soon as you release the gas valve plunger that you push to light the pilot? If it goes out again then everything I said before stands. If not and the pilot stays on for a while only to come back later and its off, then you need to check one more thing. Sometimes down drafts in the chimney can blow the pilot out and make it seem that the thermocouple is faulty. If you do not have a strong bright blue pilot flame that can weather an occasional down draft that can occur, then you need to adjust the flame as that is the cause of your issue.

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