Immersion heater thermostat

28 Nov 2017
Reaction score
United Kingdom

I've got a house with a loft conversion including a shower room. Water supply is independent of rest of house - cold water header tank, vented cylinder, electric immersion heater and a big pump. Works a treat - usually...

Thermostat on immersion heater tripped yesterday, I reset but it tripped again. Installing the cylinder looks like it was tricky - there is not a lot of space. The side of the cylinder is reasonably accessible but the top only has about 6 inches or so of space between cylinder and roof. Unfortunately the immersion heater has been inserted through the top... Options seem to me to be:

1) Take cylinder out, change heater, refit. Deal with same problem again in X years when next immersion heater fails
2) Take cylinder out, replace heater with side mounted one, refit. Cylinder only has top entry point so am I right to assume you can drill into cylinder to add new immersion from the side and screw a cap over the old hole? Or would I need new cylinder?
3) Leave cylinder in situ, drill new entry for side mounted immersion and add new heater, leaving old on in place - might be tricky fitting new one in past the old heating elements
4) As for (3), but remove old heater bending/breaking it as we go to force it out in very confined space
5) Remove thermostat only, replace with the shortest one I can find - is there any need for the stat to go to the lower reaches of the tank?

Cylinder is 1050mm tall x 450mm diameter

Sponsored Links
Option 5 won't work, the shortest thermostat is 11" so still won't fit. Even if it did, you will find that it will switch the heater off with only the top part of the cylinder heated, so a lot less hot water.

It is possible to cut a hole and add another side element, but for a proper job this requires brazing the threaded flange to the side of the cylinder. You can get flanges which fit without brazing, but there is a good possibility of those leaking.

A new cylinder with side immersion is probably the easiest choice, although more expensive. However if you have a go at fitting a side element to the existing one and it all goes wrong, you will need a new cylinder anyway.
Thanks Flameport, what I think you are saying is go back and do what should have been done in the first place - often sound advice
Sponsored Links
Yes the guy who fitted the cylinder was a bit naughty there should have got a bottom element in it
I've put in the mechanical flanges and they do work but I seal them with really good tarry sealant
And don't get any on the threads.Bob

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local