My CH system has a Potterton EP2000 control unit, which works fine, however when i last switched it off to replace a faulty valve, the time disappeared [usually stays displayed] and i had to re-program. I know that the controller contains a backup cell, can this be replaced? how do i get to the cell [never taken controller off wall!!]

Derek Elsley, February 2009

There's a little slot on the right hand of the bottom of the unit. Switch off the mains, push a screwdriver blade into this, and the whole of the front flips off, revealing the works on the back of it. The battery is a green thing in one corner on mine, which lasted 18 years before it died! Get a replacement from a good plumbers supplier. Take note of which is the + contact on the unit and battery-- on my unit the board was not marked at all!

BryanL, February 2009