immersion thermostat keeps tripping

micks_address · 20-09-2024 10:29AM #1

hi folks,

recently the thermostat keeps tripping on the immersion - its less than two year old tank and the rcd etc doesnt trip. I can reset the thermostat and it works the next night but then trips again. I'm wondering if it would have a two year warranty if i get onto my plumber or is it worth getting a new stat and having it wired or could it be a bigger immersion problem?

Cheers,

Mick

hydrus21 · 20-09-2024 10:53AM

I found some of the cheaper stats do this.

John.G · 20-09-2024 02:36PM

https://www.boards.ie/discussion/2058369752/immersion-thermostat-keeps-tricking

Can you take a photo of it with the cover removed, it may be a indirect cylinder with a heating coil which may have tripped it.

micks_address · 20-09-2024 04:20PM

Yep it's an indirect cylinder. The gas flow temp is set to 55 and the thermostat is set to 65. The stat is working as you can hear it click if you turn down the temp setting on the dial

Wearb · 20-09-2024 04:34PM

Do you have a boiler stove?

Any recent changes to the wiring?

micks_address · 20-09-2024 04:39PM

No wiring changes. Have an eddi that I use as a time clock to turn on the immersion each night on cheap electricity. At first the thermostat seemed to only trip after a power cut, had a couple a month or so ago but then it started happening every night. Nothing else heating the water apart from gas

John.G · 20-09-2024 04:50PM

Is it a top mounted dual (or single) element Immersion and is the control stat (the one you hear clicking) separate to o/temp stat which is attached to the top of the immersion boss or is it a combined contol and o/temp stat?, what make?

micks_address · 20-09-2024 05:26PM

Here's a picture. It's top mounted. It looks like it's a separate probe which is sitting lose in the top of the tank

John.G · 20-09-2024 07:31PM

It may be just the photo but looks like a bit of overheating maybe due to a lose connection at the nearest terminal, just isolate the power to the immersion, remove the wiring and simply pull up and remove the stat, its inside in a dry pocket. Is it a single or dual element immersion with a sink/bath c/o switch? If so, then its the neutral thats switched ike it seems to be in yours, if a single element, then the live is normally switched but shouldnt make any difference operationally, if nothing obviously wrong maybe just renew it, they are not overly expensive.

micks_address · 20-09-2024 07:44PM

Single immersion. Just one element

John.G · 20-09-2024 07:55PM

Here's one with a separate o/temp stat and switching the neutral, a twin element.

Damien360 · 20-09-2024 08:13PM

I have the exact same element and it did exactly the same tripping and I would reset it via that little hole on it every so often. I had pics here on another thread but it turned out to be my timer had wiring that was too thin a gauge and it eventually burned the timer. Got in an electrician and he wired a new timer with much larger gauge of wire. Hasn't tripped once since that.

micks_address · 20-09-2024 08:15PM

https://www.boards.ie/discussion/comment/122637872#Comment_122637872

The wiring I have was put in by an electrician who installed the eddi solar diverter. It doesn't look like light cable

John.G · 21-09-2024 08:50AM

I think you have a 18" stat, if so, I see your problem, just disconnect the two wires and pull it out, its the vertical element is the problem, will revert with a few numbers, later.

John.G · 21-09-2024 03:16PM

This may not be your problem if you havn't got the separate top mounted O/temp stat, I don't know how the O/temp stat works in the combined unit, the underside of the stat might juse sense the temp in the top of the cylinder and the o/temp will then trip at ~ 80C.

These rod type stats as far as I know measure the average temperature, so assuming you start off with a cylinder of cold water at todays cold water temp of 18C then the whole cylinder will heat up uniformly to 65C (your setting) and the stat will close the contacts to start re heating at ~ 55C when HW is drawn off. The vertical heating element increases the water temperature uniformly, for example if you draw off a 1/2 tank of water and start reheating then the 1/2 tank at 65C will increase say to 70C and the water in the bottom 1/2 will increase from 18C to 23C. My calcs show that when some HW is drawn off and 4" of the stat (assuming a 18" stat) is immersed in the cold water at 18C, (the remaining 14" will still be at 65C) then the stat average temperature will be at 55C and reheating will begin, if no further HW is drawn off then the stat will re open the contacts (at a average stat temp of 65C) but the 14" of the 65C water will now have reached 75C and the 4" of the 18C water will have reached 23C or something like that, it mightn't quite work like that but there can certainly be a substantial difference between the water in the cylined top and the stat setpoint temperature depending on the volume of HW drawn off.

micks_address · 21-09-2024 05:11PM

Thanks for the detailed post. It sounds plausible. Especially as I'm using both immersion and gas to heat the cylinder. What's the solution?

John.G · 21-09-2024 08:37PM

I think you should take the temperature from a hot tap after the stat cuts out normally and if you can catch it after it trips on the O/temp, there must be dozens of this type of installation around and yours worked for 2 years or so without problems?

micks_address · 21-09-2024 08:48PM

https://www.boards.ie/discussion/comment/122640920#Comment_122640920

Yeah no major issues, used to trip the odd time but not every night.

Lenar3556 · 21-09-2024 11:54PM

I would be inclined to replace the stat. It’s a simple swop without any drain down and will eliminate both a faulty duty and high limit stat.

micks_address · 22-09-2024 04:31PM

Ate there better stats or just go with the same again?

https://www.screwfix.ie/p/tesla-dual-safety-thermostat-18-/89445

John.G · 22-09-2024 05:49PM

Tesla havn't a great name due I think to the o/temp stat failing. Maybe try one of these.

https://www.backer.co.uk/collections/thermostats?srsltid=AfmBOopW4EG63wnlgHDh5Zm5hn5KvSeT_tmD_XBXcjJ0MSCx8Knisce3

micks_address · 22-09-2024 06:13PM

Thanks was looking at this, have free shipping from Amazon

Thermostat: 18in Resettable resettable 18" immersion heater rod thermostat 18" Resetable immersion heater rod themostat:

https://amzn.eu/d/aLLPkkp

micks_address · 23-09-2024 12:19PM

Phoned plumber this morning and he's going to replace the stat. Sure will see how it goes

John.G · 23-09-2024 12:36PM

Santon Immersion Nov 1972.jpg

When he takes out the old one, if you can lay hands on it, you might take a photo of the underneath of the top, I`d like to see if the o/temp is part of this, in contact with the top of the immersion. My 52 year old one has no rod type stat but has separate contact type ones one, the sink, is set to 65C, the other, the bath, is set to around 80C!! The change over switch is conveniently located right on top of the immersion. Its a Santon and cost 7 old pounds in Nov 1972. Will post a photo later for posterity.

micks_address · 31-03-2025 09:50AM

https://www.boards.ie/discussion/comment/122637381#Comment_122637381

Hi folks,

Plumber replaced the immersion few months ago now - but i noticed its stopped working last few days - took top off again and the switch had popped out but also noticed this wire had broken off its connector. Ill phone the plumber again - the cover looked like it had some slight burn marks on it as well. It didnt trip the rcbo though. Looks like these are just bad immersions or design in general? i only use the immersion at night to heat the cylinder and then gas during the day to keep it topped up. Have serious regrets that i didnt put a bigger tank in a couple of years ago and something a bit better as this has given too much hassle. Current tank is 130 litres and with 4 of us and running a shower of it could do with 200 or maybe bit bigger. Its manageable at its current size as i use a temp sensor on the tank which triggers the hot water zone from the gas when it drops below a certain temp. 30 minutes of the gas gets it back up to temp.

Annoying all the same.

Thanks,

Mick

p.s. apologies @John.G i wasnt home when the plumber replaced the immersion last so i couldnt get a look at it

John.G · 31-03-2025 10:25AM

The broken off wire is a different problem to your other one IMO.

This problem, if only occuring after using the gas fired coil might be because (even if unlikely) the temperature in the cylinder top is reaching 80C even though the cylinderstat is set to 55C, it depends on where the cylinderstat probe is attached/inserted, can you show a photo of the coil inlet and outlet piping and the position of the cylinderstat probe in relation to these positions.

micks_address · 31-03-2025 10:34AM

https://www.boards.ie/discussion/comment/123313125#Comment_123313125

Hi John,

What does that grey wire do? I phoned the plumber and he's arranging a call out - re the gas temp ive boiler flow temp set to 60 so i dont think the cylinder could ever get to 80?

Ill try pop up a picture later this evening. The tripping hasnt occured since the immersion was last replaced in September / October last year.

Thanks,

Mick

John.G · 31-03-2025 12:16PM

If the other end of that circled wire is connected to one terminal of the stat then its (single element) is wired unconventionally. Normall you will have a 3 wire cable, live (brown), blue (neutral) and a earth wire. The live will go into one terminal of the stat, the other stat terminal is connected with another wire to one of the element terminals and the blue (neutral) from the cable connects to the other element terminals, so the stat is switching the live. The earth wire should be connected to the body (top) of the heating element.

Your stat appears to be switching the neutral, you have the live (brown) connected to one of the element terminals, the circled grey?? wire is (if) connected from the other element terminal to one stat terminal and the other stat terminal is connected to the cable blue (neutral) so the stat appears to be switching the neutral, both should work as the neutral is allways switched with a dual element stat.

micks_address · 31-03-2025 12:36PM

Thanks

I'm concerned that the Rcbo didn't trip. Obvious burn marks on the immersion cap

John.G · 31-03-2025 12:56PM

The RCBO had no reason to trip on either overload or earth leakage. The broken wire just acted as a additional resistance either due to a slack terminal screw or a partially broken wire which then just overheated due to the high current draw, hundreds of appliances go on fire due to this, you should see the photos of burned out electric showers.I would think a new length of wire will sort it out, your electrician will check that the wire thickmess (csa) is adequate.

micks_address · 31-03-2025 01:37PM

https://www.boards.ie/discussion/comment/123313595#Comment_123313595

Thanks yes just heard a few horror stories recently of immersions going on fire and burning down properties. I dont like the way it was wired. I'm not an electrician but to me the wire that broke was unnecessarily bent at a tight enough angle which probably didnt help

immersion thermostat keeps tripping

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