There is a leak from behind the combustion chamber below the expansion tank which has got worse recently. It does lose pressure but always has done slightly even after replacing the pressure relief valve. The diaphragm and some of the seals were replaced a few years back. The water is dripping from the centre of the metal plate below the expansion tank as can be seen (just)
in attached photo. I am in Norwich and would appreciate any suggestions and help offered including from any qualified reasonable local engineer who might be able to sort my problem.