Immersion thermostat replacement

Daniogroove

Hi

My immersion stat keeps tripping once its reaches temperature so I have to pin reset it each time. When replacing is it just a straight swap? Does it sit inside a channel in the tank or do I need to drain it or anything before changing?

Thanks

John.G

Is it a top mounted dual immersion??

You don't have to drain the cylinder whatever type of overtemp stat is installed. some have the control (normal) stat in a dry pocket about 11" long with the overtemp stat just sitting on top of the immersion, others, I think have the two combined in both, can you post a photo, or say if its like the one below, if its like the one below, its more than likely that its the control stat (blue one) has failed on. you can adjust that (may have to tear the seal) and just turn the setting screw up and down and you should hear a click each time, if not it needs renewing, note its setting (normally 60C) before test. Also ensure immersion switched off before test and ensure isolated at the consumer unit/fuse board if changing the stat.

Immersion Latest.jpg

The Continental Op

https://www.boards.ie/discussion/comment/120702724#Comment_120702724

If the stat is tripping I suspect the OP has a stat which has a trip built into it so can't use the standard one in your picture.

A standard one will work but won't have the trip which is a separate safety component in your picture.

I think the OP might want one like this (dependant on length) https://www.screwfix.ie/p/tesla-dual-safety-thermostat-11-/48571 which has a second resettable high temp cut out built in.

John.G

His photo will reveal all.

Daniogroove

It looks the same as in the photo from what I can see. I just put the button to reset the stat each time or am i missing something?

It's a dual immersion but only the batg connected.

John.G

Has this always been tripping g like this or is this just recent?.

The stat is set correctly to 60c so suggest doing the click test as suggested above.

Not sure if it's wired correctly but will have a better look shortly.

Daniogroove

It's been in place for years but never used it but we got solar pv installed so excess is used to heat the water before exporting back to the grid. It worked fine initially but the pv installers only used a 3 core cable, now we had a sink/bath switch, just a 20a isolator but because we never used it we didn't pass any heed. I got the installer back thinking he'd replace the cable, no just both elements in series 🙈 thermostat wasn't stopping it then, I've put it back to just bath element but i think their bodge has broken the stat. Hasn't been right since.

John.G

If he has connected the two elements in series then (assuming each elememt is 2.5kw) you will now only get 1.25kw or if both are 3kw, only 1.5kw, is there a reason for this??, if he connected them in parallel the total output is either 5kw or 6kw drawing either 22A or 26A.

He may have bypassed the control stat, can you just switch off the power and disconnect one wire from any side of the (blue) control stat, then see if the immersion still operates

The Continental Op

OP can you with the power OFF to the immersion lift up that little connector block to the right of your photo and take another one so we can better see how its all connected up.

If you are running this only of excess solar pv then you only need the bath element connected.

Daniogroove

https://www.boards.ie/discussion/comment/120704896#Comment_120704896

This might be better.

The Continental Op

This needs checking but from what I can see you have the sink element connected currently and the bath disconnected. I'm sure John will put me right on that if I've got it wrong but after just wiring one this week (well changed switch and had to trace what went where) I think the terminal without the connection (has a brown wire connected in Johns photo) is the bath (longer) element.

Edit> The whole fitting looks something like this

and you want the longer element connected to heat the maximum amount of water.

John.G

Yes, what he has done is, he has connected the live to the common "bar" for both elements (this is the common neutral normally with the stat switching it) and has taken the neutral off just one, possibly the bath, the live does appear to be connected via the overtemp stat and then the control stat so looks like the control stat is knackered, (possibly the o/temp stat but unlikely since its resetting), so carry out that test and see what happens (clicking?). More difficult to check to see if the bath is in fact the live element, a multimeter may check it if the resistances are different, the bath beig the lower resistance but sometimes both elements are the same power, If the bath element is connected then most of the cylinder will be hot, if the sink is connected then only about a foot of the cylinder top ~ 30/35ltrs will heat up and you will quickly run out of water.

The Continental Op

https://www.boards.ie/discussion/comment/120705237#Comment_120705237

I think its connected up the way someone not used to dual elements would connect it with the live being switched by the trip and thermostat. With a dual element you have two separate potentially live wires and because you don't know which is going to be used you have to put the trip and thermostat on the neutral. Or you could say its connected the correct way for a single element.

In the picture you posted I'm fairly sure the brown goes to the bath element and the bath to the sink. Again fairly sure that the normal convention on is dual element immersion is that black is sink and brown is bath (they are normally pre wired). I took this picture of my own and wrote down the connections Brown - Bath, Black - Sink, Blue - Neutral. Because I've wired them the wrong way before. Very annoying to have a bath and find you only have a sink full of hot water :-(

John.G

Remembered as Sink the black down the brown bath.

Daniogroove

Both elements are 2.85kW alright. The control stat clicks when adjusted too. I can check the resistance of each element but where is the other end of each one so i can isolate them?

The Continental Op

If they are both 2.85kW then the resistance check is futile because both will have the same resistance. A résistance check is only any use of the power requirement and hence the resistance of each element is different.

On the few I've installed the sink has had a slightly lower wattage than the bath so you can check which is which because the bath will have a LOWER resistance than the sink element. Bath around 16 ohms and Sink around 24 ohms.

If your immersion cover is marked 2/2.85kW I think that means 2Kw and 2.85kW not 2x 2.85kW?

Edit....

Obviously only check resistance with the power off.

On your picture the terminal with no connection will probably read around 16 ohms between it and the wo ends of the immersion heaters that are connected together (opposite side of the fitting to the terminal with no connection). The terminal with the blue wire connected to it will probably read around 24 ohms again to the two ends of the immersion heaters that are connected together, both measurements +- a couple of ohms. ie my guess is no connection is one end of the bath connection and the blue connection is to one end of the sink connection (neutral currently goes to the common connection where one end of both are connected together). - Hope that makes some sense?

Daniogroove

https://www.boards.ie/discussion/comment/120705428#Comment_120705428

Thanks will give that a go later. If you're right about 2/2.85kW then that would put it on the sink element as it only ever draws 2.1kW max.

John.G

As you have a multimeter, with power off, disconnect both wires on the stat, and place the probes on the stat terminal screws, turn the stat to minimum and you should get a o/c, turn the stat up and you should get 0 ohms or 0.2/0.3 ohms.

Daniogroove

https://www.boards.ie/discussion/comment/120705581#Comment_120705581

Will do, trying to get some painting done along side all this and kids home soon so will check it all out this evening and report back. Cheers lads

Daniogroove

Okay so the stat is testing fine, open when turned down and 0.1 - 0.2 ohms when set to 60C.

18.6 Ohms for the unused element and 26.2 for the working element.

You both know your stuff!

I should be good so to move the live to the bath element and move over the neutral? I might have some crimps around, if not I'll get some tomorrow.

The Continental Op

https://www.boards.ie/discussion/comment/120706761#Comment_120706761

Leave the live where it is. Its attached via the cut out and thermostat to one end of both of the heating elements, thats correct for wiring a single element. Just move the blue neutral from the terminal its connected to the one with no wire (to its left).

John.G

You should be OK to just move the neutral from the sink to the bath, even though the live is connected to the common bar for both elements the current will only flow through the bath element (once neutral changed over), the electrician might have have reasoned that as now only one element is used its electrically more correct to switch the live.

You still have this overlimit tripping, just ensure yourself that (as it seems to be) the live goes to the connector block, then to the o/temp stat, then from the o/temp stat to the control stat, then from the control stat to the the common element(s) common bar. If so looks like the o/temp stat is faulty and switching off the power too soon as it shouldn't operate until ~ 85C, some of those o/temp stats are only glued to the cylinder top so you may be better off removing both the o/temp stat & the control stat and replacing both with the dual stat as shown in post #3?.

Daniogroove

Cheers lads, I had emailed elemex looking for a wiring diagram but never heard back. It's now taking 2.9kW so definitely on the bath element now alright, I'll let the solar heat it for free tomorrow and see does it trip out again but I'm confident that's it.

I thought it was on the sink just from the volume of water, how much power it was taking to heat it and for such short times I knew something was wrong. The pv installer sent a different electrician out who made it all worse and the tripping started. So hopefully back to rights now. I still might just run a 4 core myself so on the dull days I still might have enough excess to heat the sink volume.

Thanks again!

John.G

Immersion Wiring Schematic.jpg

Just remember, if you do run a 4 core then have that stat switching the neutral.

(Schematic courtesy of Bruthal)

The Continental Op

https://www.boards.ie/discussion/comment/120706995#Comment_120706995

Somewhere I think I have the bit of paper with the wiring diagram that I got with the element? If I ever find it I will post it so it can be referred back to as this isn't the first time we've had questions on wiring dual element immersions.

Daniogroove

The water started heated alright today but reset again after only a short time. I've reset it and it's continued heating so will monitor it. At this rate I'm beginning to wonder am I better off replacing the whole thing.

John.G

I would suggest but only as a TEMPORARY measure to just by pass the overtemp trip to prove its the the problem, I wouldthen install the dual stat.

Ce

The Continental Op

Its not to difficult to replace the whole thing but the cheapest and easiest course of action is to remove the cut up trip from the circuit and replace the thermostat with the one I linked to in post #3 (as John has also suggested).

The brown live wire on the supply cable would go directly to the new thermostat. You'd remove the connector block and the wires to the cut out.

Cost if you use the screwfix thermostat with built in trip is going to be €19 with no need to drain the tank. We know the heating elements work.

Daniogroove

Well lads, I got the dual thermostat in the end, working away fine since. Thanks for all your help!

The little chamber the stat drops into it; is that only capable of taking the 11" stat like the original. I ask because it's a 24" element which should bring it right down past the oil stat. But i do still think the volume of hot water is well than with the oil. Is that just the way it usually is verus a coil or would a longer stat (if possible) ensure more water to heated to temp?

The Continental Op

Its a dual immersion. No good having an 18inch thermostat down below the short sink element.

Daniogroove

Yes but I only have 3 core cable coming to it so I'm using the bath element

The Continental Op

https://www.boards.ie/discussion/comment/120750726#Comment_120750726

But you won't have a pocket for anything larger than an 11inch thermostat, take a look back to the picture in post #11, your immersion heater will look very similar.

If this isn't satisfactory then a Willis heater may give you more hot water in the tank? https://www.boards.ie/discussion/2058243718/fitting-a-willis-immersion-heater

John.G

The problem with the 11" stat and a 24" element is that, depending on HW usage, you could end up with only "11 inches" of HW at 52C to 60C and "13 inches" at maybe ~ 25C, the 11" stat will only ensure a "24 inch" volume at 60C from a cold cylinder and if all the hot contents are used up then again. The Willis heater is certainly worth considering or a destatification pump.

Daniogroove

I was looking at the destat pump alright, solar diverter has an output to power it too so it would all be run from solar. Part of me also thinks maybe to make the investment in a stainless steel tank with two side elements and never have to worry about it for years.

John.G

A bit of caution if you intend to have a coil as well, the bottom immersion element is normally above the top of the coil so you may end up only heating ~ 50% of the cylinder, back to square one, you may be able to get a cylinder with the element below the coil so have a look.