Boiling water

Hi there. I've just got home to find water in my boiler literally boiling - top water box too. I had the booster on earlier (but thought it was off). It was probably boiling for about four hours.

I recently changed the settings on the thermostat setting box on the wall, but thought that only affected the heating. Could that be it?

Other forums say it could be a faulty thermostat, but I'd like to rule out user error first.

Thanks

You don't state which model you have.

If a PC 2000 it might well be the rod stat in one or both heaters.

Check the water level too.

Mike