thorn m80/100b boiler. the pilot light will ignite but as soon as i lift the button it goes out. any answers please
pilot wont stay alight
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Is the wire from the thermocouple firmly connected to the gas valve? Does the pilot light flame impinge directly onto the thermocouple end?
If so, then you probably need a new thermcouple.
To understand why a bad thermocouple will cause the problem you're having, use the Search feature of this web site to search this plumbing/heating forum for a thread called "Solder Ring Tee valves/joints" posted by psarinuk and read the post in it by me that explains how a gas valve typically works.
If so, then you probably need a new thermcouple.
To understand why a bad thermocouple will cause the problem you're having, use the Search feature of this web site to search this plumbing/heating forum for a thread called "Solder Ring Tee valves/joints" posted by psarinuk and read the post in it by me that explains how a gas valve typically works.
Hi Nester-kelebay
Found the thread mentioned and comment from you re solder joints but would be interested to see your mentioned comment on how a gas valve works. Have just started a thread with my problem
Regards Paul
Found the thread mentioned and comment from you re solder joints but would be interested to see your mentioned comment on how a gas valve works. Have just started a thread with my problem
Regards Paul
I'm not a plumber, but I had the same problem in the last house, and it was the thermocouple.
Essentially, when you press the ignition button on on your boiler, the pilot light ignites and heats the thermocouple (just looks like an ordinary piece of wire located at top of flame). When the thermocouple is warm enough, it opens the gas valve allowing the gas to enter the main burner, and the main burner ignites, you can then release the ignition button.
As it's a problem inside of the burner unit, it's not a DIY job
Essentially, when you press the ignition button on on your boiler, the pilot light ignites and heats the thermocouple (just looks like an ordinary piece of wire located at top of flame). When the thermocouple is warm enough, it opens the gas valve allowing the gas to enter the main burner, and the main burner ignites, you can then release the ignition button.
As it's a problem inside of the burner unit, it's not a DIY job
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How some gas boiler pilot light thermocouples work
It is an electrical device consisting of two dissimilar metals joined together at two joints if you heat one joint and keep the other joint cool a small voltage is produced. The thermocouple used in many gas boilers consists of a thin metal tube with a second dissimilar conductor down the middle at the pilot light end is the hot joint in the form of a tip at the other end is the elecrical connections the small bulb on the end is insulated from the outer tube by a small insulating washer. When you screw this into the gas valve the nut and outer tube connects to the metal body of the valve and the centre tip makes contact with a metal terminal that is insulated from and passes through the gas valve body. This contact is then connected inside the gas valve to the winding on the pilot light solenoid, the other side of the winding is connected to the gas valve body completing the circuit. The power produced by heating one end of the thermocouple is not sufficient to actually open the solenoid however it is suffiecient to hold it open once it has been opened mechanically. So you hold down the button with your finger which holds open the solenoid mechanically you light the pilot which heats the thermocouple until it produces sufficient voltage and current to keep the solenoid open, you can then let go of the button.
When changing thermocouples i have known tiny pieces of metal drop down and form a short between the threaded sleeve and the centre contact so if the new thermocouple does work try cleaning out this area first.
I have also seen on other web sites that some universal thermocouples do not produce a high enough voltage for some boilers and can therefore work erratically.
It is an electrical device consisting of two dissimilar metals joined together at two joints if you heat one joint and keep the other joint cool a small voltage is produced. The thermocouple used in many gas boilers consists of a thin metal tube with a second dissimilar conductor down the middle at the pilot light end is the hot joint in the form of a tip at the other end is the elecrical connections the small bulb on the end is insulated from the outer tube by a small insulating washer. When you screw this into the gas valve the nut and outer tube connects to the metal body of the valve and the centre tip makes contact with a metal terminal that is insulated from and passes through the gas valve body. This contact is then connected inside the gas valve to the winding on the pilot light solenoid, the other side of the winding is connected to the gas valve body completing the circuit. The power produced by heating one end of the thermocouple is not sufficient to actually open the solenoid however it is suffiecient to hold it open once it has been opened mechanically. So you hold down the button with your finger which holds open the solenoid mechanically you light the pilot which heats the thermocouple until it produces sufficient voltage and current to keep the solenoid open, you can then let go of the button.
When changing thermocouples i have known tiny pieces of metal drop down and form a short between the threaded sleeve and the centre contact so if the new thermocouple does work try cleaning out this area first.
I have also seen on other web sites that some universal thermocouples do not produce a high enough voltage for some boilers and can therefore work erratically.
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paulmedd said:
Paul:
Sorry, I guess I posted the wrong thread. The correct thread is entitled:
"Thorn M Boiler - Problem maintaining the pilot flame alight"
posted in this Plumbing & Central Heating forum by davidnicole on Jan. 30
Basically, in a nutshell, what I say is:
a) a gas valve contains of two electromagnetically operated valves arranged in series so that no gas will flow completely through the gas valve unless both electromagnetically operated valves are open.
b) The first electromagnetically operated valve get's it's power from a thermocouple or thermopile sitting in a pilot light.
c) gas must flow through this first electromagnetically operated valve before it can flow up the pilot tube to the pilot light, so if the pilot light is burning, that means the thermocouple or thermopile is producing enough voltage to operate this first electomagnetic valve.
d) the second electromagnetic valve is operated by the voltage produced by a thermopile or from a transformer, and controls the flow of gas to the main burners of the appliance.
e) a thermopile is typically used on hot water heaters which don't require a household power to run a circulating pump or blower, and is simply a whole bunch of thermocouples connected in series within one component.
f) the voltage produced by both thermocouples and thermopiles will drop in time, and they periodically need to be replaced because of this.
So:
1. if a pilot light won't stay lit, the most common cause is that the thermocouple or thermopile needs to be replaced because it's not producing enough voltage anymore.
2) if the pilot light is burning, it means the thermocouple or thermopile is producing enough voltage to keep the first electromagnetically operated valve open. And, my understanding is that if there's enough power to keep that first electromagnetically operated valve (called the "safety electromagnet") open, then there is enough power to operate the second main valve to the burner trays.
3) On an appliance that has household voltage available to it to operate a circulating pump or blower, then the gas valve will use the power from a transformer to operate that second electromagnetically operated valve. So, if the pilot light is burning on a boiler or forced air furnace, but the gas valve isn't opening, check for the correct voltage at the wires going to the gas valve. If there is voltage between those two wires, then the problem is likely to be that the gas valve needs to be replaced. If there is no voltage there, the problem is that voltage is not getting to the gas valve to open it, possibly because of a safety device stopping the voltage from getting to the gas valve.
Non sequitur!I'm having the same problem, as soon as I stop pressing the button, the pilot goes off. It's 1am and it's a very very cold night. I will appreciate any suggestion.
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It's probably the thermocouple.
When a pilot light goes out... it's probably the thermocouple.
When a pilot light won't stay lit... it's probably the thermocouple.
Don't matter who asks the question. Don't matter how often they ask.
If the pilot light isn't burning... it's probably the thermocouple.
It's only AFTER changing the thermocouple and finding out it didn't make any difference that you should be phoning a heating contractor.
That way, 90 percent of the time, you save the cost of having to phone a heating contractor.
When a pilot light goes out... it's probably the thermocouple.
When a pilot light won't stay lit... it's probably the thermocouple.
Don't matter who asks the question. Don't matter how often they ask.
If the pilot light isn't burning... it's probably the thermocouple.
It's only AFTER changing the thermocouple and finding out it didn't make any difference that you should be phoning a heating contractor.
That way, 90 percent of the time, you save the cost of having to phone a heating contractor.
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