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Default Faulty Thermostat or faulty installation

Next door neighbour has just had their HW tank replaced under
maintenance contract by BG. The old tank was copper but I think the new
one is SS - it is certainly very flat topped (still open vented).

They transferred the immersion heater (the immersion heater is not used
and is a back up for boiler failure only) and thermostat from old tank
to new but now they seem unable to get satisfactory HW temperature.

One minute it is scalding hot, reduce the thermostat setting by 1Deg and
the water ends up dropping to luke warm before the boiler wakes up to
warm it up.

When moving the thermostat manually there is about a 5C "backlash"
between switch on/off operations.

Any suggestions as to whether this is

1) a thermostat that didn't like being moved and has failed due to the
disturbance

2) Lack of thermal connection between the new tank and the thermostat
(should there be any form of heat transfer compound between them) - I
think this would be my first point of call if it was my tank)

3) Incorrect positioning of the thermostat

4) any other ideas.

He has the maintenance contact with BG so they will be called in to fix
it but he would like some confidence that the problem can be fixed.


--
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Default Faulty Thermostat or faulty installation

Chris B wrote:

Lack of thermal connection between the new tank and the thermostat


Is it the strap-on with curtain wire, or shoved in a pocket/tube type?
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Default Faulty Thermostat or faulty installation

On 18/04/2021 10:55, Andy Burns wrote:
Chris B wrote:

Lack of thermal connection between the new tank and the thermostat


Is it the strap-on with curtain wire, or shoved in a pocket/tube type?


Its held on with a flat metallic strap about 5mm wide that goes right
round the tank.

--
Chris B (News)
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Default Faulty Thermostat or faulty installation

On Sunday, 18 April 2021 at 10:58:21 UTC+1, Chris B wrote:
On 18/04/2021 10:55, Andy Burns wrote:
Chris B wrote:

Lack of thermal connection between the new tank and the thermostat


Is it the strap-on with curtain wire, or shoved in a pocket/tube type?

Its held on with a flat metallic strap about 5mm wide that goes right
round the tank.

--
Chris B (News)

Whereabouts on the tank is it? It should normally be about 1/3 of the way up, too high and because hot water rises it will constantly monitor the water temperature where it is hottest so the bottom half of the tank does not warm up.

Richard
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Default Faulty Thermostat or faulty installation

On 18/04/2021 11:03, Tricky Dicky wrote:
On Sunday, 18 April 2021 at 10:58:21 UTC+1, Chris B wrote:
On 18/04/2021 10:55, Andy Burns wrote:
Chris B wrote:

Lack of thermal connection between the new tank and the thermostat

Is it the strap-on with curtain wire, or shoved in a pocket/tube type?

Its held on with a flat metallic strap about 5mm wide that goes right
round the tank.

--
Chris B (News)

Whereabouts on the tank is it? It should normally be about 1/3 of the way up, too high and because hot water rises it will constantly monitor the water temperature where it is hottest so the bottom half of the tank does not warm up.

Richard

Well I haven't actually measured it but yes at a guess I would say its
about 1/3 of the way from the bottom

--
Chris B (News)


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Default Faulty Thermostat or faulty installation

On 18/04/2021 10:38, Chris B wrote:

When moving the thermostat manually there is about a 5C "backlash"
between switch on/off operations.


Is that just the normal hysteresis of 5 to 10C?


1) a thermostat that didn't like being moved and has failed due to the
disturbance


It is probably a simple bi-metal strip with little to go wrong - except
in moving it the installer has created a high resistance electrical
connection - wire connected with screw through the insulation and only
just making electrical contact.


2) Lack of thermal connection between the new tank and the thermostat
(should there be any form of heat transfer compound between them)* - I
think this would be my first point of call if it was my tank)

The strap may not be tight enough to hold the thermostat tightly against
the tank. As far as I'm aware no compound is used between the tank and
thermostat


3) Incorrect positioning of the thermostat


Where is it positioned? The position may only be relevant to what
temperature you set it to. Currently on by tank I have installed two
(Ebay special) temperature probes/displays. One half way down the tank
where the thermostat is fitted and one at the very top. While water is
heating from cold there is a approx a 10C difference in reading with the
top of the tank being hotter.




4) any other ideas.

He has the maintenance contact with BG so they will be called in to fix
it but he would like some confidence that the problem can be fixed.




--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk
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Default Faulty Thermostat or faulty installation

On 18/04/2021 11:08, Chris B wrote:
On 18/04/2021 11:03, Tricky Dicky wrote:
On Sunday, 18 April 2021 at 10:58:21 UTC+1, Chris B wrote:
On 18/04/2021 10:55, Andy Burns wrote:
Chris B wrote:

Lack of thermal connection between the new tank and the thermostat

Is it the strap-on with curtain wire, or shoved in a pocket/tube type?
Its held on with a flat metallic strap about 5mm wide that goes right
round the tank.

--
Chris B (News)

Whereabouts on the tank is it? It should normally be about 1/3 of the
way up, too high and because hot water rises it will constantly
monitor the water temperature where it is hottest so the bottom half
of the tank does not warm up.

Richard

Well I haven't actually measured it but yes at a guess I would say its
about 1/3 of the way from the bottom


Is the tank insulated? Normally on a foamed copper cylinder, you would
cut a pocket in the foam to allow the stat to make contact with the
metal. Many of the SS cylinders are dual skinned with a metal outer
cover over the insulation, which in turn is over the inner cylinder.
This could make the stat unable to "feel" the change in temperature
effectively, and also make it such that even a quite substantial
temperature change in the cylinder is reflected in a small change
visible to the stat.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/
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Default Faulty Thermostat or faulty installation

Surely the thermostat is measuring the water temp not the tank temp is it
not?. Why did they not fit a new one? They are cheap items after all,
compared to a new tank.
Brian

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"Chris B" wrote in message
...
Next door neighbour has just had their HW tank replaced under maintenance
contract by BG. The old tank was copper but I think the new one is SS -
it is certainly very flat topped (still open vented).

They transferred the immersion heater (the immersion heater is not used
and is a back up for boiler failure only) and thermostat from old tank to
new but now they seem unable to get satisfactory HW temperature.

One minute it is scalding hot, reduce the thermostat setting by 1Deg and
the water ends up dropping to luke warm before the boiler wakes up to warm
it up.

When moving the thermostat manually there is about a 5C "backlash" between
switch on/off operations.

Any suggestions as to whether this is

1) a thermostat that didn't like being moved and has failed due to the
disturbance

2) Lack of thermal connection between the new tank and the thermostat
(should there be any form of heat transfer compound between them) - I
think this would be my first point of call if it was my tank)

3) Incorrect positioning of the thermostat

4) any other ideas.

He has the maintenance contact with BG so they will be called in to fix it
but he would like some confidence that the problem can be fixed.


--
Chris B (News)



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Default Faulty Thermostat or faulty installation

The first type are as useful as a chocolate fireguard in my experience, do
these still exist?
Brian

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"Andy Burns" wrote in message
...
Chris B wrote:

Lack of thermal connection between the new tank and the thermostat


Is it the strap-on with curtain wire, or shoved in a pocket/tube type?



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Default Faulty Thermostat or faulty installation

Brian Gaff wrote:

The first type are as useful as a chocolate fireguard in my experience, do
these still exist?


Yep 15 quid from screwfix, if you've got a hot water cylinder with
separate lagging, there's nothing wrong with a strap-on stat, it's what
I have here.

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Default Faulty Thermostat or faulty installation

If it is a double skinned tank then surely it has the pocket type thingy for
one of those thermostats?At least then it will be in the standard place and
no bits of left over insulation will be causing issues.
Brian

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"alan_m" wrote in message
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On 18/04/2021 10:38, Chris B wrote:

When moving the thermostat manually there is about a 5C "backlash"
between switch on/off operations.


Is that just the normal hysteresis of 5 to 10C?


1) a thermostat that didn't like being moved and has failed due to the
disturbance


It is probably a simple bi-metal strip with little to go wrong - except in
moving it the installer has created a high resistance electrical
connection - wire connected with screw through the insulation and only
just making electrical contact.


2) Lack of thermal connection between the new tank and the thermostat
(should there be any form of heat transfer compound between them) - I
think this would be my first point of call if it was my tank)

The strap may not be tight enough to hold the thermostat tightly against
the tank. As far as I'm aware no compound is used between the tank and
thermostat


3) Incorrect positioning of the thermostat


Where is it positioned? The position may only be relevant to what
temperature you set it to. Currently on by tank I have installed two (Ebay
special) temperature probes/displays. One half way down the tank where the
thermostat is fitted and one at the very top. While water is heating from
cold there is a approx a 10C difference in reading with the top of the
tank being hotter.




4) any other ideas.

He has the maintenance contact with BG so they will be called in to fix
it but he would like some confidence that the problem can be fixed.




--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk



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Default Faulty Thermostat or faulty installation

On 19/04/2021 07:50, Brian Gaff (Sofa) wrote:
If it is a double skinned tank then surely it has the pocket type thingy for
one of those thermostats?At least then it will be in the standard place and
no bits of left over insulation will be causing issues.
Brian



To answer all the questions at once, it seems to be foam covered (best
equivalent picture I can find on the net is like this - although not
this brand)

https://www.wolseley.co.uk/product/g...ainless-steel/

The thermostat is definitely measuring (or trying to) the outside
temperature of the tank and not the water.

the fitters have cut out a section of foam about half a mm bigger than
the thermostat (just like the thermostat fitment on my own clyinder).
Might they have not fully cleared the foam from the side of the tank?

--
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Default Faulty Thermostat or faulty installation

Chris B wrote:

Might they have not fully cleared the foam from the side of the tank?


I think only you can answer that! Remove the strap and have a look.

Tim

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Default Faulty Thermostat or faulty installation

On 19/04/2021 10:21, Tim+ wrote:
Chris B wrote:

Might they have not fully cleared the foam from the side of the tank?


I think only you can answer that! Remove the strap and have a look.

Tim


once you have made sure that all the foam has been removed from
the cylinder where the thermostat makes contact, ensure that it
makes good mechanical contact with the cylinder.

if you have some thermal grease, the stuff used with CPU cooling
'radiators', put a smear of that on the tank before refitting the
thermostat.
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Default Faulty Thermostat or faulty installation

On 18/04/2021 15:52, John Rumm wrote:
On 18/04/2021 11:08, Chris B wrote:
On 18/04/2021 11:03, Tricky Dicky wrote:
On Sunday, 18 April 2021 at 10:58:21 UTC+1, Chris B wrote:
On 18/04/2021 10:55, Andy Burns wrote:
Chris B wrote:

Lack of thermal connection between the new tank and the thermostat

Is it the strap-on with curtain wire, or shoved in a pocket/tube type?
Its held on with a flat metallic strap about 5mm wide that goes right
round the tank.

--
Chris B (News)
Whereabouts on the tank is it? It should normally be about 1/3 of the
way up, too high and because hot water rises it will constantly
monitor the water temperature where it is hottest so the bottom half
of the tank does not warm up.

Richard

Well I haven't actually measured it but yes at a guess I would say its
about 1/3 of the way from the bottom


Is the tank insulated? Normally on a foamed copper cylinder, you would
cut a pocket in the foam to allow the stat to make contact with the
metal. Many of the SS cylinders are dual skinned with a metal outer
cover over the insulation, which in turn is over the inner cylinder.
This could make the stat unable to "feel" the change in temperature
effectively, and also make it such that even a quite substantial
temperature change in the cylinder is reflected in a small change
visible to the stat.


BG installers could not be so stupid...could they?
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