hot water too hot - thermostat or valve or something else?

[AlF2008]

There is no immersion heater so its definitely not the cause

I had the system drained down at the weekend and after refilling I had the HW turned off while trying to get house warmed up and the radiators bled. the flow pipe for the HW was warm/hot but the return was pretty cold which suggests to me that the valve either isn't letting by or its by a small amount. Does that make sense?

I'll turn the HW off when I get home and wait for it to cool down. Then I'll check the pipes.

 

[AlF2008]

Last night I had the hot water off for most of the night. While the heating was still on, I checked the flow and return pipes. The flow was warm, return cold. I'm presuming that as the flow is further up the boiler that it will be warm if there is hot water in the tank?

New thermostat still hasn't arrived but hopefully will by the end of the day.