3 port duo valve system fault. Hot water too hot

[Lincsman]

Just started looking for a fault on my Y plan system - the water is too hot and does not respond to the cylinder stat.
I've noticed that although the cylinder stat is turned down ( not calling for heat ), when the CH stat is turned up ( calling for heat ) both systems are heated ( rads and hot water ).

My first assumption is that the mid position valve is not closing the HW port when the cylinder stat is satisfied, allowing the flow in both directions and overheating the hot water.

Before I change the valve, has anyone got any other suggestions or things that should be checked.?

The programmer has been changed for another fault (battery faulty) and also the pump (seized). The valve did get very hot when the pump seized and I'm just wondering whether this has caused it to stick etc.

 

[bathjobby]

Sounds about right as the temp out of the boiler is something like about 85c and its normally your tank stat (55c ish) which regulates your water temp. So if the tank stat is out of play (not calling for heat) due to you continually pushing 85c water through it, thats what will be in your tank. Have you tried manually shifting the position of the valve to a: see if it is seized b: it makes a diff ?

 

[Lincsman]

Thanks Bathjobby.

Not tried moving it manually yet, that's my next move which I feel more confident to do now you agree with my thoughts.

I'll take the top assembly off and see how it moves. Is it best to replace the valve section if it has been stuck or will a good wiggle sort it out.