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The Home Smithy
The Home Smithy, Tradesman
Category: Plumbing
Satisfied Customers: 9622
Experience:  Tradesman
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I have a pub and the thermocouple keeps burning out on the

Customer Question

I have a pub and the thermocouple keeps burning out on the boiler can I bypass it or do you know why it keeps failing after only about 2 weeks.
Submitted: 8 years ago.
Category: Plumbing
Expert:  The Home Smithy replied 8 years ago.


You can not bypass the thermocouple. Without it you would have to severly modify the gas/fuel valve/pump in order to make it operate properly.

How thermocouples work is by electrical voltages produced by heating the bulb at the end of the unit. This electrical charge is measured in millivolts (millionths of a volt) This small electrical charge operated an electromagnet that applies a minute amount of pressure on a valve that allows the pilot light to recieve fuel. It also allows the other valves in the main valve body to open up and supply fuel to the main burners.

If these keep failing on a regular basis you need to look for something that is frying the electric generator or the magnetic properties of the thermocouple. This can be something as simple as a speaker magnet set too close to the unit. It may also be a transient spike of electricity from something.

I once went to a friends parents home to repair their computer. They said that they had it repaired only a few days before by a factory repairman. But that was their last free service call. They were allowed three. After speaking with them they took me into the den to look at the computer. The lady ran a day care at her home, and there of course were finger paintings, and color crayola drawings posted everywhere.Especially dense was the compter caseing. There were magnets holding at least 50 or more little pieces of paper with miscellanious things on them. I asked her if they had always been there. "No," she said. "Only for the past couple weeks. The unit used to be in the desk". I removed all the magnets (these were good neodynium magnets. Nice and strong to keep all the paper attached), and then reloaded the opsys. She never had problems with it again that I know of.

. This is the type of thing you need to look for. Something that even a tech would be hard pressed to notice. A wire touching the metal of the unit, a speaker, or even the flame of the pilot up too high. Unless you are a very unlucky person there is an underlying reason for this unit to be blowing this many thermocouples.

Please post any other concerns you may have here.

Best, THS

Expert:  Rick replied 8 years ago.
It is highly unlikely that successive thermocouple replacements would burn out every few weeks. You probably have an underlying problem such as an intermittent failure of the main gas control valve. How do you know the thermocouple is burnt out? Is the end melted or does it have a hole in it? If you are losing the pilot because of this most likely the problem is in the main gas control valve and not the thermocouple. DO NOT ATTEMPT TO ELIMINATE THE THERMOCOUPLE IS IS A PRIMARY SAFETY DEVICE. Without it you could fill your pub with gas.
Customer: replied 8 years ago.



I have recenctley moved here and it is quite an old boiler that was not working So I had a new gas valve fitted and it works fine now however it seams to have some kind off adjustable overheat thing on it and the boiler kept cutting out so I temporarly bypassed this and that solved one problem but I still have a problem as it works fine for between 2 and 4 weeks then cuts out and will not light untill I replace the thermocouple I think the pilot light may be to high but im not sure.

Expert:  The Home Smithy replied 8 years ago.


First off what is the make and model number of your unit. I will see if I can locate a service manual for it.

What you need to do is determine if there is an adjustment for the pilot. This is in the form of a screw recessed into the body near where the pilot gas tube exits the main valve body. You will want to turn it down (to the right clockwise) until only about 1/4" of flame is actually touching the thermocouples bulb. From there adjust it only if the flame is burning yellow anywhere except for the very tips of the flame. This should give you the proper heat at the thermocouple. If the unit does not remain lit then adjust a bit more flame out.

One other thing to look for is what I call torching. This is where the flame of the pilot is partially obstructed and it causes a flame that resembles a mini torch. This can almost always be determined from the hissing sound the flame makes compaired to the silent operation of the normal pilot.

Please let me know if I can be of further assistance.

Best, THS

Customer: replied 8 years ago.

Hi I have attempted to lower the pilot light as you sujested I found two Brass screws on the body of the gas valve one let gas out and the other did not seem to do any thing but on closer inspection of the thermocouple it apears to pertrude through the pilot light and when the main burners come on the touch it as well I have been to the plumb centre and they tell me it is the right length 900 mm i was thinking of getting a universal one and adjusting it so it only goes into the pilot light then seeing what happens unless you can think off any other reason for them failing so often.


Kind Regards


Expert:  The Home Smithy replied 8 years ago.

I think that is a good plan, Trevor. If the thermocouples bulb is too long it will extend into the main burners flame and this will overheat the thermocouple.

The main burners put out a lot more heat than a single pilot will. So if there is one pilot light hitting it and two of the main burners flames are hitting it you have three times the normal amount of heat that the thermocouple is used to recieving. This burns out the thermocouple in short order.

Go ahead and do as you planned. I believe that this will solve the problem.


As for the screw that didnt do anything. That one is for the main burners and should be adjusted while they are operating.


please post any other concerns you may have here. If I have answered your question please be sure to click the accept link next to my answer.


Best regards, XXXXX XXXXX Smithy