I am trying to understand how the thermocouple on my boiler works as I
have bent the copper pipe and need to know whether this is stopping
the thermocouple from working.

As far as I can tell, the end that resides near the flame is just a
pointy outside bit and needs to be heated up for 20 seconds to keep
the pilot light going. There is a long length of thin copper pipe that
bolts into the side of the manifold that is the source point for the
pilot gas supply.

On the end is what seems to be a metal or lead ball which rests on a
plastic plate that slots into place. This plastic plate has a strip of
metal on it. in the thermocouple copper pipe there seems to be an
internal cable that must somehow contact with metal on the plastic
plate.

Now, heres the cruncher ... with no power turned onto the boiler where
does the electrical charge that must bridge the copper and plastic
metal strip come from?

I'm baffled ... it seems that this is an electrical switch but there
is no power???

Can anyone enlighten me??

jON

I'm baffled ... it seems that this is an electrical switch but there
is no power???

Can anyone enlighten me??

I'm not sure if I quite follow what you describe, having never seen inside
the gas valve. However, a thermocouple actually generates electricity
directly from the heat. They are used in old boiler designs because they
work even without a power supply. Old boilers tend to only require a call
for heat signal and have no permanent live, so the pilot control must work
without the use of mains electricity.

Christian.

"Christian McArdle" wrote in message
. net...
I'm baffled ... it seems that this is an electrical switch but there
is no power???

Can anyone enlighten me??

I'm not sure if I quite follow what you describe, having never seen inside
the gas valve. However, a thermocouple actually generates electricity
directly from the heat.

Correct.

They are used in old boiler designs because they
work even without a power supply. Old boilers tend to only require a call
for heat signal and have no permanent live, so the pilot control must work
without the use of mains electricity.

The basic safety gas controls of a boiler/gas appliance a

1. Thermocouple valve
2. Governor
3. gas solenoid valve.

These were all separate valves on a pipe inside the appliance. In large
boilers they still are. In the 1960s they were all integrated into one
casting called the multifunction control valve, which is on the Spacesaver

The thermocouple generates a small current, enough to power a solenoid valve
which supplies the pilot light, but only when the valve is on its seating.
Enough to hold it down. That is why you have to turn a knob (the pilot gas
tap) and hold down the same the knob for 30 seconds) pushing the valve onto
its seating; enough time for the thermocouple to energise the solenoid and
hold the valve on its seating maintaining a pilot light. If the pilot light
disappears the solenoid de-energises and drops to its seating stopping all
gas to the appliance. Another solenoid valve further upstream is in the
main gas valve which is usually mains powered.




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The multifunction valve is the manifold at the other end of the Pilot
Pipe from the Piezo I presume?

I understand the principle now, but is a kink in the thermocouple
outer sheath likely to stop the thermocouple from working ...

we tried to get a spanner around the pilot nut and pushed the
thermocouple outer sheath into a little "v" shape and broke the
insulation on the Piezo at the same time which now refuses to work.

It looks like the Piezo, thermocouple head and Pilot are in a block
and need to be replaced together - is it possible to buy and fairly
eay to fit each of these components individually?

If so, how can I check that its all working ... is there a way to
check the charge generated by the thermocouple?

jON

"Jon Rowlan" wrote in message
om...
The multifunction valve is the manifold at the other end of the Pilot
Pipe from the Piezo I presume?

I understand the principle now, but is a kink in the thermocouple
outer sheath likely to stop the thermocouple from working ...

It depends on how sharp the kink is. Thermocouples are cheap. get another
two and have one inside the boiler in case.

we tried to get a spanner around the pilot nut and pushed the
thermocouple outer sheath into a little "v" shape and broke the
insulation on the Piezo at the same time which now refuses to work.

Then buy an new peizo electrode.

It looks like the Piezo, thermocouple head and Pilot are in a block
and need to be replaced together - is it possible to buy and fairly
eay to fit each of these components individually?

They slide out of the block. Look harder, they are usually secured in some
way to the block.

If so, how can I check that its all working ... is there a way to
check the charge generated by the thermocouple?

There are some device to check these, but expensive. Get another
thermocouple and a spare in case. They are cheap. ...and new peizo
ignition electrode.




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"Jon Rowlan" wrote in message
om...
I am trying to understand how the thermocouple on my boiler works as I
have bent the copper pipe and need to know whether this is stopping
the thermocouple from working.

As far as I can tell, the end that resides near the flame is just a
pointy outside bit and needs to be heated up for 20 seconds to keep
the pilot light going. There is a long length of thin copper pipe that
bolts into the side of the manifold that is the source point for the
pilot gas supply.

On the end is what seems to be a metal or lead ball which rests on a
plastic plate that slots into place. This plastic plate has a strip of
metal on it. in the thermocouple copper pipe there seems to be an
internal cable that must somehow contact with metal on the plastic
plate.

Now, heres the cruncher ... with no power turned onto the boiler where
does the electrical charge that must bridge the copper and plastic
metal strip come from?

I'm baffled ... it seems that this is an electrical switch but there
is no power???

Can anyone enlighten me??

jON

A Thermocouple generates a very small voltage (mV) which is then used to
sense heat; the voltage is generated by the thermal excitation of a junction
of two dis-similar metals. Run a Google on Thermocouple if you want to delve
deeper.

"Martin" wrote in message
...

"Jon Rowlan" wrote in message
om...
I am trying to understand how the thermocouple on my boiler works as I
have bent the copper pipe and need to know whether this is stopping
the thermocouple from working.

As far as I can tell, the end that resides near the flame is just a
pointy outside bit and needs to be heated up for 20 seconds to keep
the pilot light going. There is a long length of thin copper pipe that
bolts into the side of the manifold that is the source point for the
pilot gas supply.

On the end is what seems to be a metal or lead ball which rests on a
plastic plate that slots into place. This plastic plate has a strip of
metal on it. in the thermocouple copper pipe there seems to be an
internal cable that must somehow contact with metal on the plastic
plate.

Now, heres the cruncher ... with no power turned onto the boiler where
does the electrical charge that must bridge the copper and plastic
metal strip come from?

I'm baffled ... it seems that this is an electrical switch but there
is no power???

Can anyone enlighten me??

jON

A Thermocouple generates a very small voltage (mV) which is then used to
sense heat;

Uh!


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