Replacing boiler thermostat

[SCOTT495]

Firstly I know very little (if nothing about Boilers) but wish to lear

and eventually be able to maintain my own boiler myself and this seem a good place to learn how to start.

I have a 'Direct Combination Cylinder' boiler and my white mete heating has recently stopped working (the lower cylinder). I believ this may be the thermostat and I wish to change this myself but haven? the slightest clue how to proceed. Before I buy a thermostat Im going t switch my top and bottom ones to see if this fixes the problem (althoug I will have to wait overnight to find out). Ive also been told to pus the reset button before doing anything on my boiler to see if thi fixes it, but I cant find the button. I am confident enough to chang the thermostat myself, but I would rather ask advice before attemptin it.

Please can someone let me know what I should do and in what order (obviously switch the power off at the mains first) but afte that???... (yes I know that little about boilers) and also where th reset switch would lilkley be?

I have attached some photos.

Thanks very much for any advice in advanc

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[Set Square]

Firstly, you need to sort out the terminology!

What you've got ISN'T a boiler - it's a hot water cylinder heated by two immersion heaters.

If one of these has stopped working, it *could* be the thermostat but it's just as likely - maybe *more* likely - to be the electrical heating element in the immersion heater.

I can't quite make out all the wiring in your picture, but the red thing is the thermostat. The live side of the supply cable will go to one side of the stat, and the other side of the stat will be connected to one side of the element. The neutral side of the supply will be connected to the other side of the element.

You need to switch everything off, and disconnect enough to be able to get at the cables going to the element - and then check with a suitable meter that you have continuity across the element.

If this sounds totally foreign to you, it's probably safer not to touch it but to call in a qualified electrician instead.

Incidentally, your stat is currently set at 80 deg - which would be dangerously (scaldingly) hot if it actually managed to achieve that!

[Ed Sirett]

One or two more points.

If thermostat needs replacing then you are likely to need a short (7") one. Anyway the old unit will be a guide.

Replacement units will now have a cutout button on the thermostat which can only be reset by pushing it.

80C is very hot - but since this is off peak heating it is important to get the water a hot as possible. IIRC there is a relaxation of the 65C max rule for off-peak storage water heating. However great care must be used when using this water.

If the element needs replacing then you are info some serious work if you have not done one before.