Heating issue with boiler

The noise could be movement of the pipes or indeed, a leak; although, you would probably have seen evidence of that. You mentioned that you lost pressure. There could be a leak on your system or in the boiler. It could be the pressure relief valve that is leaking or the heat exchanger. You need a Gas Safe Engineer to check.

The heating pipe are always under pressure & have water in them. So if there was a leak it would leak even if the heating was off. If it was leaking in the floor you'd see it coming through ceiling at some point. Unless it's extremely slow. If the boiler is losing pressure does the pressure gauge rise when heating to over 3bar, if so it's the expansion vessel. First thing to do is get a service and ask them to recharge the expansion vessel & check prv. If that all ok, you can likely get success from a leak sealant into the system for minor leaks which won't cost much

Depends on sounds/ how often you loose pressure?

-The expansion vessel needs replacement or 2Divert valve fault and stuck on hot water as soon as the heating on the divert valve leaks and then loses pressure the boiler

The noise could be movement of the pipes or indeed, a leak; although, you would probably have seen evidence of that. You mentioned that you lost pressure. There could be a leak on your system or in the boiler. It could be the pressure relief valve that is leaking or the heat exchanger. You need a Gas Safe Engineer to check. Read less

The sounds you can hear is circulation noise there are chemicals for noise reduction it’s worth dosing your system with that because I’m assuming this noise is a recent occurrence. Also if your system is constantly losing pressure regularly (daily, weekly) and not annually then more then likely you have a seeping leak.