"Set Square" wrote in message
...
In an earlier contribution to this discussion,
wrote:

my ideal isar he35 has been fine for the last 6 weeks since fitting
until this week, i noticed the pressure had dropped to 0.75 bar from
the usual 1 bar (recomended when cold) i topped it back up to 1 bar
and it held this until the central heating had been on again, when it
had again dropped to 0.75 bar. This has continued all week it never
drops below 0.75 and works o.k. i can see no apparent leaks and the
pressure release valve has not discharged any water, the maximum
pressure reached when running is 2 bar. The only mention in the
handbook of 0.75 bar is the pressure at which the expansion tank is
pre pressurised at. has anyone any ideas

thanks in advance

Stick a pot or something under your overpressure relief pipe, and see if it
fills up with water. If your expansion vessel is buggered then upon firing
up, the pressure will rise, the expansion vessel will not accomodate that
pressure rise and the overpressure relief valve will operate ( at about 2.5
to 3 bar ) dumping water out of the 15mm pipe that presumably emerges
outside your house wall somewhere. Then belatedly you look at the system
pressure and find it's dropped down to 0.75 bar.

That's one possibility anyway. If you keep filling up the system with mains
water to repressurise it eventually all the inhibitor in your system will be
flushed away and your boiler and radiators will start to corrode etc.

Andy