Oil Boiler, Water Too Hot

[foxyferret]

My mum has an oil boiler about 3 years old with a hot water tank in the airing cupboard. The dial on the tank is set on 60 degrees where it has always been OK. Suddenly the hot water has gone extremely hot. We have tried turning it down to about 40 degrees but it has made no difference. She lives in a bungalow so all on the same level. Could this be the thermostat?

[Ryzen]

Could be the cylinder stat , the diverter valve,or a wiring fault between the 2.

[The Builder]

Yes, I agree. It's most likely a faulty cylinder stat.

[foxyferret]

Thank you both, the plumber is coming on Monday to check it out.