Hot Water Cylinder Problem

[Matalan]

Hello, we have a Honeywell L641A1039 CYLINDER THERMOSTAT CONTROL
fitted and turned down to 40 (the lowest setting)...however the water is reaching a very high temperature. This is happening even when the water is in the OFF position on the programmer LANDIS+STAEFA RWB9.
I would appreciate any help at all please with my process of elimination. Thanks

 

[Newboy]

It's possible that your three port valve (assuming you have one) is stuck so that when you are running your central heating the water is constantly being heated. If you set you programmer to heating off / water on see if the radiators still get warm.

If the valve is stuck then it could be either mechanical fault - the paddle is jammed or an electrical fault with either the drive motor or the microswitches

 

[Matalan]

Thanks for your reply. I have something that says Honeywell F49713 which has a lever and three positions...main, open and auto. The lever is set at the auto position. Is this correct please? I have given this a light knock with the heel of my hand.

 

[gas4you]

Sounds about right. If this is very old valve you may have to change the entire unit.

 

[Matalan]

Thank you for your reply. I have just checked the lever again and noticed it wasn't Fully down into the auto position. It is now, so I will wait and see how it goes. Thanks again