Glow Worm Compact 80E switches on without the tap !?

This morning I heard clicking and went to the boiler and noticed the domestic water heater switches on and off - without anyone using the hot (or cold) water tap !?

I switched the unit on and off and opened the tap a bit and even turned on the radiator. But now as soon as the boiler is turned on it starts heating domestic water and won't stop (water actually gets hot and it's usable via the tap).

I got worried that if water is not used and if it just keep heating it inside, it would get damaged or blow up !?!? Is there a danger of that... !?

Two years ago the Hot Water Micro Switch (with Diaphragm) started leaking which I bought a new one and changed it myself and there was no problem ever since until today. Is there a problem with that switch again ? (I recall if that switch has problem the boiler doesn't come on with the tap, now it's other way around !?)

Any suggestions appreciated....

(The boiler is about 10 years old and not serviced for a while.)