Why does my HW come on with CH even when switched off!

[plumberhelp!]

Our Potterton EP2 was old and the sliders for HW/CH were loose. We couldn't get CH without the HW on! So I put a new digital EP2 on. It fit over the old backplate : no wiring required! What I found then was that if I put HW on with the slider then fine - digital display come on "Hot Water" and one red light comes on. If however I put CH "on" with slider it immediately switches both red lights including for HW as well (even though slider for HW is off) but only the digital display for "Heating" comes on. We get loads of HW with CH until HW gets so hot stat switches both off!!. I've tried everything : put new backplate on programmer / new Drayton mid point value / new actuator : still the same. Checked the wiring to the chart that came with the Drayton : its correct. Checked the cylinder tank stat : correct. At a complete loss. Beginning to wonder if a fault with the Potterton itself why would the red light and the digital display be internally inconsistent???!

 

[Deleted member 120897]

Sounds like the potterton could be set to a gravity hot water system. Have a look on the back for the setting.

 

[plumberhelp!]

Sounds like the potterton could be set to a gravity hot water system. Have a look on the back for the setting.

Thank you so much I reset to pumped and its fixed it!!I assumed that because water to feed the copper cylinder came from a header tank it was gravity but of course thereafter it is pumped. Wish I'd gone on this forum before I replaced everything! Note for interest : Screwfix/Toolstation : drayton 3 way valve plus actuator : £62 actuator on its own : £82!!