Hi, please could some one help I have a Ariston Microgenus HE, the heating is working okay but when I turn the hot water tap on the digital temp starts at around 30 then starts to rise to mid fourty's water is hot out of the tap then suddenly it says 99 and water runs cold. Is this the Thermostat switch faulty, or some thing more?

Sam, November 2009

Blocked Plate Heat Exchanger or Diverter Valve, its a job for a Registered Gas Engineer

www.elanar.co.uk, November 2009