The physics is very simple, there is a leaking somewhere in the system! The leaking can only be at one of these three parts: 1. boiler pressure relief valve (PRV), or 2. boiler main heat exchanger, or 3. on external pipes and valves. But to find out an actual leaking point is sometimes not straightforward by just one visit. We wrote this Diagnosis Strategy to help our customers on understanding the problem.
As a Herts Boilers standard policy, we offer “no fix no fee” to most of our repairs, but unfortunately for a pressure problem on a sealed system we will charge by the number of visits, not by the outcome, although we will do our best to find out the leaking and get it fixed. The reasons behind this exception are: 1. if it is boiler main heat exchanger leaking, some customers will go for a new boiler, or we don’t always get main heat exchanger replacement jobs. 2. We are not an expert on external pipe leaking fault finding (external pipes mean the pipes outside the boiler which are all over your house).
Once your boiler is losing pressure on a regular basis, it is also suggested to check around your house, ie, is there any radiator valve leaking, is there any wall corner damping, or is there any floor board wet?