Replacing boiler thermostat?

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

-- SCOTT495

the picture looks like a water heater element.

is this a boiler or water heater?

also from the temp numbers i guess those are degress C so you are probably in Europe and maybe they call water heaters boilers over there?

mark