Central heating system won't maintain pressure.

[Chugg]

A couple of months ago I had a new boiler fitted along with new radiator valves fitted onto the existing radiators which vary in age, (oldest is around 30 years). The central heating system is a sealed system which when needed, you have to top up the system via a loop valve.

The problem I've got is that I simply cannot get the system to maintain it's pressure with the boiler switched off. The system drops down to 0.0 bar within a matter of hours from turning off the boiler. The heating system is fine with the boiler on. I'm unable to find any leaks on any of the radiators or on the boiler either. I'm worried that I may have a leak under the floor somewhere but it's a ground floor flat and I'm thinking that it's a concrete floor. If anybody could help me with this I would greatly appreciate it.

 

[easyflow]

assuming your talking about a combi, if you are sure there are no surface leaks and the pressure releif valve is not letting by, you have a problem with the expansion vessel, if that check out ok.
You will need to have the heating system drained and an air pressure test done by disconnecting the flow and return from the boiler with one end capped and pressure tested at the other, either way you will need to get someone in to do this

 

[sooey]

Top it up to one and a half bar and turn off the isolating valves on the flow and return pipes into the boiler.
If it holds it's pressure the leak is on the system somewhere other than the boiler.

 

[kevoffthetee]

Given the number of problems I've had with my boiler, it could be the pressure release valve or the expansion vessel