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Immersion Thermostat wire burns out

Discuss Immersion Thermostat wire burns out in the Central Heating Systems area at ElectriciansForums.net

Still and all, the measured element resistance is 14 ohms or 16.43A at 230V, so, is it really outrageous to use a 20A stat to switch this?. Daughter's 2.5kw immersion still has the same 15A skol (or shol?) stat switching it for the last 16 years, so 15A switching 10.87A.
 
With reference to the 20A control stat I discovered this while searching for its technical specification: ​

Cotherm
TSD01106
Thermostat​

Cotherm TSD01106 20A Control Thermostat
A Cotherm brand adjustable control thermostat with a range of approximately 5°C - 85°C.
The TSD01106 is a rod thermostat with single pole break-on-rise action rated at 20A 240v. The stem (rod) is 265mm long and 7.5mm in diameter making suitable for use in all standard 280mm x 8mm (11" x 5/16") thermostat pockets. It is ideal for use in commercial products for direct control of single phase loads up to 3kW or to operate a contactor for higher loads or three phase applications.
Note: This device does not include a safety cut-out and is only designed to control the water temperature.
This thermostat is NOT SUITABLE for DOMESTIC without there bring an additional a safety cut-out as required by law.
Condition: New and unused in original manufacturer's packaging.

Delivery​

Orders received before 2pm Monday to Friday will be despatched the same day. Orders received after 2pm Friday, Saturday or Sunday will be dispatched the following Monday. Orders received after 2pm will be treated as having arrived the following day.

All goods are dispatched, professionally packed, on a signed for service. In most cases our carrier can leave the goods in a safe place, or with a neighbour for no extra charge. Should you require this service please detail it in the notes when placing your order together with a contact telephone number.

If you do not receive the goods within three working days (Monday to Friday) of placing your order we would ask that you contact us. We can then investigate the problem and authorise a replacement where necessary.

If you wish to purchase more than one listed item, we can usually ship these together for a reduced overall carriage charge. In this instance please contact us before paying so that we can advise you of the combined carriage charge.

Hours​

 
Last edited:
brixtonia said:
I have a 4kW immersion heater in a thermalstore - very recently replaced by a plumber as the previous one was leaking. Supplied with a cotherm thermostat and a second pocket for a safety cutout into which the safety cutout from the previous immersion was fitted and seems to be working fine.

I smelled burning and removed the cover to find that the insulation on the wire between the cutout and the stat was melting. The end closest to the stat was clearly more affected. The stat has deformed around the point the wire connects to it and the stat has ceased to work.

The wire between the safety and the stat is exactly the same as the wire from the spur to the immersion which has been in place since I can remember. The connection seemed sound but hard to tell now.

One thing I had noticed after it was installed is that it was cycling on and off quite rapidly.

Just a faulty stat?
Click to expand...
One thing I had noticed after it was installed is that it was cycling on and off quite rapidly.

By the second it I reckon you mean the control stat. I think this control stat is acting akin to a thermal flasher device viz:

What is a Flasher Unit? | what is a Flasher Relay? - https://www.arc-components.com/blog/blinking-lights-what-is-a-flasher-unit.html

One might assume the control thermostat stat senses the temperature of only the water in the tank - but it does not. Alas the control stat will also be subjected to the Ohmic heating effect of all its electrical components through which the IH element current flows. This heating effect will increase if the IH element current is higher as is the case for a 4kW element vis a vis a 3kW one.
 
Last edited:
marconi said:
With reference to the 20A control stat I discovered this while searching for its technical specification: ​

Cotherm
TSD01106
Thermostat​

Cotherm TSD01106 20A Control Thermostat
A Cotherm brand adjustable control thermostat with a range of approximately 5°C - 85°C.
The TSD01106 is a rod thermostat with single pole break-on-rise action rated at 20A 240v. The stem (rod) is 265mm long and 7.5mm in diameter making suitable for use in all standard 280mm x 8mm (11" x 5/16") thermostat pockets. It is ideal for use in commercial products for direct control of single phase loads up to 3kW or to operate a contactor for higher loads or three phase applications.
Note: This device does not include a safety cut-out and is only designed to control the water temperature.
This thermostat is NOT SUITABLE for DOMESTIC without there bring an additional a safety cut-out as required by law.
Condition: New and unused in original manufacturer's packaging.

Delivery​

Orders received before 2pm Monday to Friday will be despatched the same day. Orders received after 2pm Friday, Saturday or Sunday will be dispatched the following Monday. Orders received after 2pm will be treated as having arrived the following day.

All goods are dispatched, professionally packed, on a signed for service. In most cases our carrier can leave the goods in a safe place, or with a neighbour for no extra charge. Should you require this service please detail it in the notes when placing your order together with a contact telephone number.

If you do not receive the goods within three working days (Monday to Friday) of placing your order we would ask that you contact us. We can then investigate the problem and authorise a replacement where necessary.

If you wish to purchase more than one listed item, we can usually ship these together for a reduced overall carriage charge. In this instance please contact us before paying so that we can advise you of the combined carriage charge.

Hours​

Click to expand...

A bit strange because they have a 4kw (at 230V) element here with a ST7 thermostat which doesn't look anything special, no mention of a contactor.
The OP has a 4kw element which he measured at 14 ohms which is more than likely 4kw @ 240V = 3.8kw @ 230V or 16.5A and is using a 20A stat!.

www.eurosales.ie

14” TITANIUM SINGLE IMMERSION ELEMENTS - 4KW - 1 3/4”BSP - 230V - SIDE ENTRY WITH STAT - TSDR7

IDL091009SC 091009SC Heating and Ventilation Ideal Elements Domestic & Industrial Elements Heating and Ventilation Water Heating Immersion 4KW Ideal 230V
www.eurosales.ie
 
Today I sent a question on current rating and immersion element power to the Backer Electric Company Limited. They confirmed as Johntheo mentioned above that their Backer stats rated 20A can indeed directly control a 4kW IH element. Whether other makes of stat can is another matter.

brixtonia: 1. The question about the rcd is to see whether the 4kW element albeit a new one is leaking current to earth - unlikely if new but maybe this is a cause of overcurrent.

2. I'd love to have some pictures of the installation to study. Are push on spade terminals used for any of the connections? Are they bare metal or shrouded types?

3. What is the supply voltage?

4. Does the installation have a large solar pv system feeding into the grid which might be elevating the local mains voltage? Are the large solar pv arrays nearby which might be raising the supply voltage?

5. Forgive me - is the wiring definitely 2.5mm2 csa?

6. The 16A safety stat is under-rated.

7. What temp do you have the control stat set at?

8. What is the length of the link between the control and safety stats?

Probably enough for now. But some images of the point of failure on the control stat external terminals would be useful to see.

:)
 
Last edited:
marconi said:
Today I sent a question on current rating and immersion element power to the Backer Electric Company Limited. They confirmed as Johntheo mentioned above that their Backer stats rated 20A can indeed directly control a 4kW IH element. Whether other makes of stat can is another matter.

brixtonia: 1. The question about the rcd is to see whether the 4kW element albeit a new one is leaking current to earth - unlikely if new but maybe this is a cause of overcurrent.

2. I'd love to have some pictures of the installation to study. Are push on spade terminals used for any of the connections? Are they bare metal or shrouded types?

3. What is the supply voltage?

4. Does the installation have a large solar pv system feeding into the grid which might be elevating the local mains voltage? Are the large solar pv arrays nearby which might be raising the supply voltage?

5. Forgive me - is the wiring definitely 2.5mm2 csa?

6. The 16A safety stat is under-rated.

7. What temp do you have the control stat set at?

8. What is the length of the link between the control and safety stats?

Probably enough for now. But some images of the point of failure on the control stat external terminals would be useful to see.

:)
Click to expand...
Firstly to answer your questions:

1) Not on an RCD.
2)
[ElectriciansForums.net] Immersion Thermostat wire burns out
3) 240
4) No solar PV.
5) That's what I specified when I bought it.
6) yes the 16A cut out stat is underrated - nevertheless it has been working for about 4yrs.
7) Temp control set at 75-80C as per manual supplied with UFH and Thermalstore.
8) 100mm approx.
[ElectriciansForums.net] Immersion Thermostat wire burns out
 
This may be resolved although I am not sure why.

I purchased a Sunvic VK4351 20A rod thermostat which I mistakenly believed had a safety cutout but did not - it is just a straightforward 20A stat. I fitted this with the 20A cotherm TSD01106 stat (mains>sunvic>cotherm>immersion) which is the same as the one supplied with the immersion. (I appreciate that this is a little pointless but I wanted to see if having removed the 16A cutout things worked OK). The connection into the 20A Cotherm quickly began to overheat as before and melt the insulation. It also cycled perhaps 10s on 40s off as before.

So I removed the Cotherm and replaced it with the Sunvik VKL2352 cutout with manual reset (the 16A cutout which has been working fine for a couple of years). So (mains > new sunvic 20A stat > old sunvic 16A cutout > immersion). And it's been working fine for a week.

I was struggling to find an 11" (or 7") rod stat which was 20A rated and had a variable temp range up to 80C and an inbuilt safety.

It seems to be the Cotherms which have been causing the problems.
 
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marconi said:
With reference to the 20A control stat I discovered this while searching for its technical specification: ​

Cotherm
TSD01106
Thermostat​

Cotherm TSD01106 20A Control Thermostat
A Cotherm brand adjustable control thermostat with a range of approximately 5°C - 85°C.
The TSD01106 is a rod thermostat with single pole break-on-rise action rated at 20A 240v. The stem (rod) is 265mm long and 7.5mm in diameter making suitable for use in all standard 280mm x 8mm (11" x 5/16") thermostat pockets. It is ideal for use in commercial products for direct control of single phase loads up to 3kW or to operate a contactor for higher loads or three phase applications.
Note: This device does not include a safety cut-out and is only designed to control the water temperature.
This thermostat is NOT SUITABLE for DOMESTIC without there bring an additional a safety cut-out as required by law.
Condition: New and unused in original manufacturer's packaging.

Delivery​

Orders received before 2pm Monday to Friday will be despatched the same day. Orders received after 2pm Friday, Saturday or Sunday will be dispatched the following Monday. Orders received after 2pm will be treated as having arrived the following day.

All goods are dispatched, professionally packed, on a signed for service. In most cases our carrier can leave the goods in a safe place, or with a neighbour for no extra charge. Should you require this service please detail it in the notes when placing your order together with a contact telephone number.

If you do not receive the goods within three working days (Monday to Friday) of placing your order we would ask that you contact us. We can then investigate the problem and authorise a replacement where necessary.

If you wish to purchase more than one listed item, we can usually ship these together for a reduced overall carriage charge. In this instance please contact us before paying so that we can advise you of the combined carriage charge.

Hours​

Click to expand...
Interesting - especially as this was the stat supplied with this 4kW immersion.
 
Good evening from London. Thank you for the information. That element has 3 separate elements wired in parallel. Could you give me manufacturer and part number for it please so I can learn more about it?
 
marconi said:
With reference to the 20A control stat I discovered this while searching for its technical specification: ​

Cotherm
TSD01106
Thermostat​

Cotherm TSD01106 20A Control Thermostat
A Cotherm brand adjustable control thermostat with a range of approximately 5°C - 85°C.
The TSD01106 is a rod thermostat with single pole break-on-rise action rated at 20A 240v. The stem (rod) is 265mm long and 7.5mm in diameter making suitable for use in all standard 280mm x 8mm (11" x 5/16") thermostat pockets. It is ideal for use in commercial products for direct control of single phase loads up to 3kW or to operate a contactor for higher loads or three phase applications.
Note: This device does not include a safety cut-out and is only designed to control the water temperature.
This thermostat is NOT SUITABLE for DOMESTIC without there bring an additional a safety cut-out as required by law.
Condition: New and unused in original manufacturer's packaging.

Delivery​

Orders received before 2pm Monday to Friday will be despatched the same day. Orders received after 2pm Friday, Saturday or Sunday will be dispatched the following Monday. Orders received after 2pm will be treated as having arrived the following day.

All goods are dispatched, professionally packed, on a signed for service. In most cases our carrier can leave the goods in a safe place, or with a neighbour for no extra charge. Should you require this service please detail it in the notes when placing your order together with a contact telephone number.

If you do not receive the goods within three working days (Monday to Friday) of placing your order we would ask that you contact us. We can then investigate the problem and authorise a replacement where necessary.

If you wish to purchase more than one listed item, we can usually ship these together for a reduced overall carriage charge. In this instance please contact us before paying so that we can advise you of the combined carriage charge.

Hours​

Click to expand...
Can you provide a link to this info? I'd like to share it with the supplier.
 
If this was fed by a three phase supply, you wouldn't be able to control it directly with a single 'stat, which possibly explains why there appears to be two 'stat pockets.
You could also fit two stats with your single phase supply, controlling two elements with one, and the third with the other. This would bring the 'stat current well within the limits of a 16A version.
 

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