I recently purchased a new flat, which has an Ariston Combi boiler (installed last year along with new heating system by previous owner). If I switch the boiler off (Eg on timer) the pressure gradually starts to drop. If left approx 8 hours or more, this drops to a level where the boiler fails to switch back on, error message appears and pressure needs to be corrected by opening water inlet valve briefly.

If the boiler is switched back on within approx 4-6 hours, the pressure is adequate to restart and gradually comes back up to a 'normal' level.

Any ideas? The person who installed the system cannot schedule a visit to me for a month, so keen to get an idea of whether this can wait or should be looked at sooner. Plus it is costly to programme it to come on every 4-6 hours to avoid this issue. Appreciate any advice - thanks!

Pamela, January 2010

This is happening to me with my Ariston boiler too, but it is NOT the pressure relief valve, as I too have had a new one, and two days ago they also drained the boiler expansion tank but that didn't resolve it either. The guy seemed stumped as to what to try next and thought to run some stuff through the system which seeks out any small leaks. I'll let you know if they resolve it as I am about to ring them yet again (thank goodness I took out insurance when I moved in to this house in Dec).

Sue G, March 2010

my ariston boiler does just the same and has to be repressurised every morning - even though the pressure relief vale(pump switch) was replaced in june 2009!

josephine, February 2010

Can't help with an answer, but my Combi A also does the same. I don't have any external leaks from rad's or pipes and it stays up if I leave it on permanent. The pressure also drops when the hot water is ran as well.
I'm afraid I'm leaving mine (expensively) not on timer until the weather warms up in the hope I get a solution.

Simon., January 2010

hi pam
theres a leak some where on the systerm if you look at the boiler it should have a pressure relife pipe going through the wall to out side look out side to see if the pipe is dripping if it is then your pressure relife valve needs changing, check all your radiator valves sometimes they weep and the pressure will drop, other than that ask the flat below if there are any damp patches appeard on there ceilings

wayne the plumb, January 2010