I have a Cotherm TSD thermostat for my hot water cylinder that has been staying on indefinitely, i.e. the water is getting far too hot.
When I turned the dial from end to end, there was no clicking sound, so the contacts were closed all the time (which I tested with a resistance meter).
Since I've always wondered how these things are supposed to work, I took it apart and cleaned the contacts.
There's a wire that goes down the tube that expands to open the contacts. I suspect that wire has stretched over the years.
When I put it back together (there's only one way of doing that), it works fine except that when I set the temperature to 30 the contacts are open circuit and for temperature 80 the contacts are closed. So it's working the wrong way around.
However if I just set the temperature to the middle, the contacts open and close correctly when the temperature varies. So the dial is the wrong way around.
When I first installed the thermostat I set it to 55 and that seemed about right, so I never noticed a problem.
Surely it's not possible for the manufacturer to label the dial wrong, but I can't see anything I have done wrong,apart from taking it apart that is, but this is a DIY group!.

On Sun, 15 Sep 2013 20:30:38 -0700 (PDT), Matty F wrote:

I have a Cotherm TSD thermostat for my hot water cylinder that has been staying on indefinitely, i.e. the water is getting far too hot.
When I turned the dial from end to end, there was no clicking sound, so the contacts were closed all the time (which I tested with a resistance meter).
Since I've always wondered how these things are supposed to work, I took it apart and cleaned the contacts.
There's a wire that goes down the tube that expands to open the contacts. I suspect that wire has stretched over the years.
When I put it back together (there's only one way of doing that), it works fine except that when I set the temperature to 30 the contacts are open circuit and for temperature 80 the contacts are closed. So it's working the wrong way around.
However if I just set the temperature to the middle, the contacts open and close correctly when the temperature varies. So the dial is the wrong way around.
When I first installed the thermostat I set it to 55 and that seemed about right, so I never noticed a problem.
Surely it's not possible for the manufacturer to label the dial wrong, but I can't see anything I have done wrong,apart from taking it apart that is, but this is a DIY group!.

If you bring it to the Northern Hemisphere it'll be OK.
--
Peter.
The gods will stay away
whilst religions hold sway

"Matty F" wrote in message
...
I have a Cotherm TSD thermostat for my hot water cylinder that has been
staying on indefinitely, i.e. the water is getting far too hot.
When I turned the dial from end to end, there was no clicking sound, so
the contacts were closed all the time (which I tested with a resistance
meter).
Since I've always wondered how these things are supposed to work, I took
it apart and cleaned the contacts.
There's a wire that goes down the tube that expands to open the contacts.
I suspect that wire has stretched over the years.
When I put it back together (there's only one way of doing that), it works
fine except that when I set the temperature to 30 the contacts are open
circuit and for temperature 80 the contacts are closed. So it's working
the wrong way around.
However if I just set the temperature to the middle, the contacts open and
close correctly when the temperature varies. So the dial is the wrong way
around.
When I first installed the thermostat I set it to 55 and that seemed about
right, so I never noticed a problem.
Surely it's not possible for the manufacturer to label the dial wrong, but
I can't see anything I have done wrong,apart from taking it apart that is,
but this is a DIY group!.

ISTR some thermostats have a switch to tell the various controllers that the
required temperature has been reached. There are labels CALL and SAT. I
assume SAT is short for 'satisfied', and this would become closed in the way
you describe. If there is only one switch, then by default, I think it will
be CALL (i.e. turn the heating on).

On 16/09/2013 04:30, Matty F wrote:
I have a Cotherm TSD thermostat for my hot water cylinder that has been staying on indefinitely, i.e. the water is getting far too hot.
When I turned the dial from end to end, there was no clicking sound, so the contacts were closed all the time (which I tested with a resistance meter).
Since I've always wondered how these things are supposed to work, I took it apart and cleaned the contacts.
There's a wire that goes down the tube that expands to open the contacts. I suspect that wire has stretched over the years.
When I put it back together (there's only one way of doing that), it works fine except that when I set the temperature to 30 the contacts are open circuit and for temperature 80 the contacts are closed. So it's working the wrong way around.
However if I just set the temperature to the middle, the contacts open and close correctly when the temperature varies. So the dial is the wrong way around.
When I first installed the thermostat I set it to 55 and that seemed about right, so I never noticed a problem.
Surely it's not possible for the manufacturer to label the dial wrong, but I can't see anything I have done wrong,apart from taking it apart that is, but this is a DIY group!.

Are you sure that it isn't a changeover switch with 3 contacts? If so,
the central (common) contact will be connected to one of the others
below the set temperature and to the other one above the set
temperature. This enables the stat to be used for both heating and
cooling applications (or sometimes for more complex heating
arrangements). Which way it operates depends on which of the contacts
you use.

If you get that wrong, it still won't work properly even at the mid
position because it will never switch on when the temperature is too low.
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

On Mon, 16 Sep 2013 11:11:03 +0100
Roger Mills wrote:

when I set the temperature to 30 the contacts are open circuit and
for temperature 80 the contacts are closed.

Surely:

If you set it to a lower setpoint (30) than the ambient temperature, the
contacts are open, so it's not telling the heater to heat. If you set
it to a higher temp. (80), the contacts close, and tells the heater to
come on.
Sounds correct.

--
Davey.

On Monday, September 16, 2013 11:07:43 PM UTC+12, Davey wrote:
On Mon, 16 Sep 2013 11:11:03 +0100

Roger Mills wrote:



when I set the temperature to 30 the contacts are open circuit and

for temperature 80 the contacts are closed.



Surely:



If you set it to a lower setpoint (30) than the ambient temperature, the

contacts are open, so it's not telling the heater to heat. If you set

it to a higher temp. (80), the contacts close, and tells the heater to

come on.

Sounds correct.

Yes of course you are correct. I just had a mental block. It's working fine now.
I only looked inside because the contacts were always closed. Perhaps the metal rod slowly stretches over 5 years, although it seems to have gone wrong over a few days. The water from the tap was much hotter than usual.
I have now fitted another thermostat.

On Mon, 16 Sep 2013 12:47:31 -0700 (PDT)
Matty F wrote:

On Monday, September 16, 2013 11:07:43 PM UTC+12, Davey wrote:
On Mon, 16 Sep 2013 11:11:03 +0100

Roger Mills wrote:



when I set the temperature to 30 the contacts are open circuit and

for temperature 80 the contacts are closed.



Surely:



If you set it to a lower setpoint (30) than the ambient
temperature, the

contacts are open, so it's not telling the heater to heat. If you
set

it to a higher temp. (80), the contacts close, and tells the heater
to

come on.

Sounds correct.

Yes of course you are correct. I just had a mental block. It's
working fine now. I only looked inside because the contacts were
always closed. Perhaps the metal rod slowly stretches over 5 years,
although it seems to have gone wrong over a few days. The water from
the tap was much hotter than usual. I have now fitted another
thermostat.

I had a similar problem, and it was caused by the zone valve on the side
of the hot water tank staying stuck open, so it never told the boiler to
shut off. The only control was the boiler's internal thermostat, the
result was much hotter water at the tap than normal.
--
Davey.

On Monday, September 16, 2013 4:30:38 AM UTC+1, Matty F wrote:

When I put it back together (there's only one way of doing that), it works
fine except that when I set the temperature to 30 the contacts are open
circuit and for temperature 80 the contacts are closed.

Sounds fine to me! Why would you expect it to work the other way round?

On Sun, 15 Sep 2013 20:30:38 -0700 (PDT), Matty F
wrote:

I have a Cotherm TSD thermostat for my hot water cylinder that has been staying on indefinitely, i.e. the water is getting far too hot.
When I turned the dial from end to end, there was no clicking sound, so the contacts were closed all the time (which I tested with a resistance meter).
Since I've always wondered how these things are supposed to work, I took it apart and cleaned the contacts.
There's a wire that goes down the tube that expands to open the contacts. I suspect that wire has stretched over the years.
When I put it back together (there's only one way of doing that), it works fine except that when I set the temperature to 30 the contacts are open circuit and for temperature 80 the contacts are closed. So it's working the wrong way around.
However if I just set the temperature to the middle, the contacts open and close correctly when the temperature varies. So the dial is the wrong way around.
When I first installed the thermostat I set it to 55 and that seemed about right, so I never noticed a problem.
Surely it's not possible for the manufacturer to label the dial wrong, but I can't see anything I have done wrong,apart from taking it apart that is, but this is a DIY group!.

Are you using the aircon contacts?