immersion thermostat keeps tripping

micks_address

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

I found some of the cheaper stats do this.

John.G

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

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

Do you have a boiler stove?

Any recent changes to the wiring?

micks_address

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

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

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

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

Single immersion. Just one element

John.G

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

Damien360

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

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

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

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

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

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

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

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

Lenar3556

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

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

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

John.G

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

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

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

John.G

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.