Water cylinder overheating

[wimbledoc]

My hot water tank is superheating, even when HW is switched off on programmer, and despite turning the tank stat right down (I get to know this is happening because the high temperature causes the shower pump to lock out)
If the CH is turned off at programmer, then HW supply does not overheat.
Any hints or tips please?
Is it the three port valve, programmer, or something else at fault?
Many thanks

 

[Agile]

I would expect it could be the cyl stat or the motor valve.

But rather that asking us who have not been at your property, it would be better to do some electrical tests or call someone who can.

Tony

 

[matt1e]

Probably the actuator but may be a short in the wiring
I take it every thing used to work ok?

Matt

 

[wimbledoc]

Probably the actuator but may be a short in the wiring
I take it every thing used to work ok?

Matt

Things seemed to go wrong after header tank ran dry. Pipes, or was it pump, made a loud screech - but after bleeding some rads the noise stopped. it was after this that the water overheating seemed to start.....or is this just coincidence.

 

[Agile]

The cylinder cannot get any hotter than the boiler flow temperature!

That would not usually exceed 82° C

Tony

 

[gas112]

82 is feking hot .
It sounds like Your motorised valve is passing so when your heating is on and HW off water is still circulating around the cylinder with no control other than boiler stat .

 

[HERTS P&D]

Is your immersion turned on?

Andy

 

[wimbledoc]

Immersion is definitely off

 

[wimbledoc]

Have fitted new three way valve head - still getting the same problem.
Should I be thinking about getting a new programmer ? - current one is a Potterton EP 300.

 

[ChrisR]

The sealing part of the valve is inside - wet. Not uncommon for them to "let by". Unfortunately!

Also the spindle can just go stiff.
What make is it ?
Take the head off, put a small spanner on the spindle, wiggle and gently squash the rubber inside by pushing against the "end stops". If it's a Honeywell it only moves a little and you stand a chance, other makes go round all the way, and it's deffo worn out.