Yes. I have a meter and know a reasonable amount about electrics. Not too sure of working with mains voltages, but I know the principles. Do you have an idea?
Sorry - I need to go out now, but will check back on here later/in the morning for any updates.
That's the main junction box - if you know what you are doing you could check that there is no voltage between brown and blue wires of the myson valve when heating turned off (with system powered up). If there is 230v then there is a problem with the controls.
Then, if there is no voltage, isolate the system, disconnect orange and grey wires of myson valve, check for continuity between them. If there is continuity then the microswitch is closed and the valve is stuck open.
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