Hot Water Problems

[bar1]

Can anyone help me with this one please? About six months ago my hot water stopped working. (Gas boiler - baxi bermuda) It would only work with the heating on. Had a new programmer fitted. Thought the problem was cured, but because it was winter, didn't realise that it was only working with the heating on. So was told to have new motorised valve installed. Had that done. Problem is now worse. No hot water at all. The pump works, the boiler works, the pipes from the boiler go up to the airing cupboard and are hot, but the cylinder refuses to get hot. If I turn off the system the immersion heater will work. Please can anyone give me a clue what it might be? I know I can't fix it myself, but would really like to know what it is. Thank you

[The Builder]

Do you have a cylinder thermostat clamped halfway up the outside of the immersion cylinder?
If that's faulty, it may "think" that the water is already hot, and stop it heating up properly................ although that doesn't quite make sense either. Faulty motorised valve does still seem the most likely.
Anyway, several people on here would have a better idea than I. Just 'ang about :o)

[bar1]

Thank you The Builder. Yes there is a thermostat on the cylinder and if I turn it down I can hear it click on and off. Hopefully someone will know. It's just frustrating because of the long weekend I can't get it fixed, so my mind has gone in to overdrive imagining all sorts of horrendous things and of course praying it's easily fixed.