Hi, I have located a long standing, intermitent leak. It it coming from the bottom of the c/h manifold, suggesting the diaphragm is needing changing.It is a Vokera RS20-80 Flowmatic ordinary combi.Is the cover plate that holds the diaphragm in situ sealed with a compound, or just reliant on the seal of the diaphragm to plate,with the 4 screws stop it leaking.?It is not affecting the operation of the boiler, just have to keep topping up regularly.