OK before you pick on me, it's a B&Q one Viso heatline 24, and yes I've read about them being crap (now) but it seamed like good value at the time.
Right now the problem on the central heating side, when it's working it's great but when it turns off after a couple of hours ( when everyones gone to bed) it looses all the pressure in the central heating and the low bar light flashes, when I come in from work I top the system up bleed rads and it's up and working, untill it again goes off then it looses pressure, so we have to fill it again, can't find any leaks....any ideas

tony

F&E tank still isolated?

Could be a few things.

Most likely the expansion vessel has either lost its pressure, or has ruptured inside.
if so the system will be pressurizing up to 3bar when running and blowing off outside, hence loosing its pressure.
Easiest fix is to plumb in an 8litre external expansion vessel from screwfix.

PRV could be dripping, again it will show outside. A new PRV is peanuts

Worst case scenario, heat exchanger could be split, turn boiler off, pressurize to 2 bar, and see if any water is running out of
condense pipe.....If so, buy a new boiler, Heatline spares are extortionate.

u2u me if you want any more advice.

Al.

Pressure vessel may have failed, when it's running does the pressure rise to above three bar.
If this is happening the pressure relief valve will dump the pressure out the wall then as it cools the pressure drops and won't relight.
check the vessel there will be a schroeder valve omit pump it up to .75 bar when the system is cold and see how you go if it keeps doing it its bolloxed.
You then have two options get a replacement for the boiler ( good luck with that )or install a stand alone vessel that can be cut in anywhere on the system.
Oh and before anyone else says it serves you right for buying a crap
Boiler.

Hth rob


Too slow how strange the same answer from two Leeds members


[Edited on 8/2/12 by bob tatt]

Sounds like the pressure is dropping faster than happened with me, but I had a similar fault that was traced to a failed copper pipe that was laid in concrete floor.

Had to isolate various parts of the heating system until we located the leg it was in, then bypassed the failed pipe.

Edited to coorict typo...

[Edited on 8/2/12 by Xtreme Kermit]