Very hot water tank

[andyc555]

Please can somebody guide me to a solution?
I have an Ideal gas boiler for central heating and hot water, both controlled via a timer. The central heating works fine (and is now switched off). My problem is with the hot water. Over the last few days I have noticed that the hot water tank has been making a noise as if the water inside is bubbling / boiling. When you turn the hot water tap on it has indeed increased in temperature. It has a Danfoss Type AT thermostat on the cylinder and the temp is set to 60 degrees, I put it down to 50 but still the same is happening. If I turn the thermostat up it 'clicks' at about 78 degrees indicating that it is being heated to that temperature. In the evening the hot water is timed to go off at 7pm yet last night the 'bubbling' was still going on at 4 in the morning.
The immersion part is definately switched off.
When I look at the boiler, although it is making a noise it does not appear to be fired up?
Currently thinking about replacing the cylinder thermostat?
Any ideas would be gratefully recieved.

 

[ChrisR]

Boiler stuck on , with a 3 port valve, would do it.
More details needed.

 

[2520years]

I don't know what it's called, but there's a metal lever on the side of the 3-port valve. If you push that across it'll slowly go back to where it started, but in the meantime it'll free up the valve inside. It's no effort, so it's worth a try.