Boiler is Potterton Flamingo.
Cylinder has a Drayto stat I changed it last year as the old one (old ACL Drayton one) was sticking and no hot water was coming on when called to.
Thanks for your help here everyone.
Them shock arresters look good. I have heard of them, but never used one. Where do you fit them, on the incoming mains in thr case of the original poster?
I have a leaking coil in my hot water tank (small tank is overflowing and big tank constantly filling. when I turn off gate valve it stops).
Would internal leak sealer (Fernox) be of any use to stop this. My mate used it on a leaking rad and it was fine and worked immediately and is still...