Problem with boiler pressure

[thames]

Hello
Hope someone can give me some advice on a problem im having with the central heating in my flat.
I have a Glowworm 18si fanned flue system boiler with 5 radiators. Over the past year I have had a problem that the boiler keeps losing pressure going to 0.6 where the red light will start flashing and then continuing to go to 0.0

It started almost a year ago and would lose pressure gradually over a couple of weeks but got quicker with time. We had a plumber come round and he fitted a Presure release valve which seemed to stop the problem for a couple of months how ever the problem eventually came back and slowly got worse.

We have had a couple of different plumbers round over the past couple of months and most recently had someone from British gas come round. He said he thinks it is a leak in the pipes somewhere and flushed the pipes with some filler. This has not helped and the system can now go from 1.8 to 0.0 in as little as an hour.

If the central heating is turned off but the hot water left on the boiler maintains its pressure, recently as a test I turned off each radiator individually at their bases and then turned the central heating on. this caused the boiler to lose pressure very quickly.

Obviously if this is a leak it will mean pulling up carpet and wooden flooring in my flat which I would rather not have to do not to mention drilling into the floor to get to the pipes is there anything else that would cause this problem. my flat is on the 3rd floor of a 3 story block and i have had no complaints from anyone below about leaks or ceiling stains from above so cant understand where the water could be going if it was a leak.

Thanks in advance for any help you can give.

[gisago]

Have you checked if the pressure gauge goes right up above 3bars before it loses all its pressure. It may be the expansion vessel.

[thegasman]

turnung every single rad off was not the best idea and i am not surprised the pressure went down very quickly as the boiler would've been heating water that had nowhere to go causing overheating and the preesure to rise and in turn causing the prv to operate. As with the previous post i agree it is probably the expansion vessel, it may just need pumping up, but worst case you have it replaced. just fill up the boiler to 1.5bar turn on your heating and watch the gauge. If it goes right up to 3 and beyond get somone to check the vessel you will probably need another prv although it might just need cleaning and greasing.