I have a Myson boiler. The water boils, the overflow pipe make a noise
like thunder as hot water overflows into the header tank in the loft
with a tremendous gush. The overflow pipe is very hot to touch, and
the water in the header tank is hot and steaming. Is this a boiler
thermostat problem? The boiler does this after a couple of hours of
being on for HW and CH and is up to temperature. When I turn the
temperature control on the boiler front panel down to off, it stops.
The pump is working. What's the likely cause, and is it a DIY job to
fix it?
Thanks
Kevin