Glowworm Swiftflow combi losing water pressure -help!

[jamescycling1]

Water pressure needing topped up daily, pretty much going to zero overnight. Had British Gas out, they say nothing wrong with the boiler, must be a leak under the floorboards. Had another guy out who replaced the PRV as he thought that was the issue but problem still persists. Had another guy out who has spotted 2 things
1. At the top of one of the radiators, when you touch it there is a tiny drop of water that comes off on your finger. The guy said this might be the problem, but becuase I was losing pressure daily he wasnt sure if this was the major cause.
2. The valve part I turn to top up the water is connected to the double check valve via a short hose. He removed the connecting hose of the doublecheck valve from the top up valve, and during the night about half a tumbler of water has steadily dripped from the open double check valve. Would this be the problem or is this another red herring.

I appreciate the problem may well be under the floorboards, but I had a quick look under one of the floorboards and the pipes (the very small amount I can see) seem lagged. The British Gas guy is coming back tomorrow (on a contract) and I want to make sure he checks everything possible before I consider ripping up floorboards.

Any help would be grateful

 

[twgas]

has the leak on radiator been fixed, it not get it done as this will cause some pressure loss - it all depends on size of system as to how much 1bar would be

 

[jamescycling1]

I cant understand this, now I have replaced the hose to the double check valve it is still leaking - it didn't before the guy removed it. Also, the pipe that goes outside is now leaking slightly onto the driveway (only slightly). Could it be the pressure vessel?

 

[twgas]

Any leaks/drips you know about should be repaired, pressure vessel may need checking to ensure it can take up any increase in pressure from heating the water in the system. the pipe outside will be connected to the PRV - this will also need checking/changing. the double check valve sounds like it need replacing, the braided hose connects thye cold main to the rad circuit, it will not, although screwed onto it, affect the check valve.

 

[jamescycling1]

Any leaks/drips you know about should be repaired, pressure vessel may need checking to ensure it can take up any increase in pressure from heating the water in the system. the pipe outside will be connected to the PRV - this will also need checking/changing. the double check valve sounds like it need replacing, the braided hose connects thye cold main to the rad circuit, it will not, although screwed onto it, affect the check valve.
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thanks, so the double check valve has not direct impact on the pressure - it just needs replaced as it is leaking - is that right?

The PRV was replaced a few days ago.