Water cylinder stat tripping

[newbuilder22]

Hi everyone,

I have an electric hot water heated unvented cylinder. The reset button keeps popping on the thermostat.

I have tested two screws reading is 14ohm

I took the thermostat out (Tesla) and put it in a tall jar filled with water at a temp of 60 c. I put a meat probe in to get a reference. I then out the Tesla thermostat in and turned the dial untili is clicked (50 C). Leaving it to cool etc it still was between 5 and 10 c out. Could this lag be causing the safety reset to trip?

The thermostat was not fully immersed in the water - there was still some copper at the top, but it was immersed by everything but about 3 inches.


Do you believe this is a thermostat lag that is causing water to get too hot and then trip? or some other reason? Do I need a new thermostat, it is only 2 years old when the stat and the element was replaced together.

If it is a new thermostat, does it have to be the same brand and if not whats your recommendation?

Thanks in advance.

 

[Stuckinarut]

Tesla thermostats are usually for immersion heaters aren’t they? Is it the immersion reset tripping? Do you have hard water?

 

[newbuilder22]

Tesla thermostats are usually for immersion heaters aren’t they? Is it the immersion reset tripping? Do you have hard water?

Yip emersion element - thought the two "water cylider and immersion were interchangeable".

Soft as they come water- NE scotland.

I have noticed though that it is a 14" Tesla element with an 11" rod - rather than 7" - will that matter?

 

[JohnD]

I think you mean the thermostat in an immersion heater. Please post a photograph of it.

What colour is the cylinder?

Is the cylinder also heated by a gas (or oil, coal or wood) boiler?

Can you lay your hands on a thermometer to test the temperature of the hot water?

 

[newbuilder22]

It is a yellow copper cylinder circa 2000. similar to https://mcdonaldwaterstorage.com/products/vented/vented-cylinders/

https://www.screwfix.com/p/tesla-dual-safety-thermostat-11-/48571

The cylinder is heated with electricity and wood pellet boiler.

The temperature of the hot water according to the Eddi is

It is side entry and tripped just after 4pm .

The wood pellet boiler will only heat to 40 degrees.

 

[JohnD]

What is a Eddi, and where is its sensor? Higher or lower than the immersion element?

Still hoping for that photo.

I think yellow is much older than 2000. But you said unvented, which will not be copper, or yellow.

 

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The sensor is a pocket in the tank - not at the immerser- slightly lower- where the box is on the left.

It is showing as lower than the cut off on the thermostat of the immerser but the immerser is cutting out and tripping.
The wood pellet burner is showing as the water being at the tame temperature as that of the Eddi so both are in agreement.

I am really struggling to explain this so -

If thermostat in immerser is set at 70 or just below then Wood boiler and Eddi are showing at between 62 and 65 before it trips.

 

[JohnD]

1) That's not unvented. Yellow is very old.

2) the sensor is below the immersion so will read a lower tempersture. The hot water stratifies at the top

3) please show us a photo of the thermostat in the immersion heater, showing the wiring connections.

 

[newbuilder22]

 

[JohnD]

Sorry. Never seen one like that before.

Is the arrow pointing at 60? I can't make it out. It does not look very old. I can't see all the wires but presumably the brown or red one goes into the stat.

They are not very accurate, try turning it down by 10, but get a new one, they are not expensive. Poke something down the stat tube to see how long it is. If I interpret the pic correctly, it is horizontal so length should not matter much.

If the sensor is in the grey box, isn't it above the immersion element? Use a thermometer to test the tap water in case there is an inaccuracy.

BTW cylinder might be light green which is newer than yellow. Current foam is blue but unvented are usually white, having a secondary metal enclosure.

 

[ree]

OP,
After reading your posts, & seeing your pics then FWIW: why not call a plumber, someone who is familiar & qualified for working on unvented.

 

[newbuilder22]

OP,
After reading your posts, & seeing your pics then FWIW: why not call a plumber, someone who is familiar with Indirect's, or a similar knowledgeable sparky?

Because the invention of forums is for asking questions. Hence that is what I was doing. Calling a sparky or plumber on a sunday at 11.15pm is a bit overkill - don't you think.

But thanks for the useful insight into your knowledge of this topic.

 

[newbuilder22]

Sorry. Never seen one like that before.

Is the arrow pointing at 60? I can't make it out. It does not look very old. I can't see all the wires but presumably the brown or red one goes into the stat.

They are not very accurate, try turning it down by 10, but get a new one, they are not expensive. Poke something down the stat tube to see how long it is. If I interpret the pic correctly, it is horizontal so length should not matter much.

If the sensor is in the grey box, isn't it above the immersion element? Use a thermometer to test the tap water in case there is an inaccuracy.

BTW cylinder might be light green which is newer than yellow. Current foam is blue but unvented are usually white, having a secondary metal enclosure.

I think it is light green - didn't know that they had standardised an aging process.

Thanks for all the pointers though,

Tap water measures same as the Eddi and water stat on the pellet boiler so all is reading the same.
The thermostat is pointing to 60c as just as you had suggested I turned it down further after the last trip.

Will probably go for the size that comes with the set and shown https://www.free-instruction-manuals.com/pdf/pa_1936606.pdf then it is the same as the element which I believe is 14"

 

[Johntheo5]

Just to be sure, if you havn,t all ready done so, switch off the power to the immersion, with the m.meter to ohms, probe across the two stat terminals, turn the stat up and down, when it clicks when you turn it down, check for open circuit, turn it up, check for continuity when it clicks. Should read 0ohms or 0.2/0.3, if this checks out then a faulty hi limit since these dont operate until ~ 85C.

 

[newbuilder22]

Turning from

70 is 0 ohm
Click heading colder is: there is no click
25 is reading 122.1kohm
Heading hotter to just before click is out of range then 0, 0.1,0.2,0.3 at click