the boiler is eight years old serviced yearly by the installer had this problem with the pressure dropping for a number of months i have had the engineer out on two occasions He changed the pressure relieve valve and done other checks e.g expansion vessel test which he said was OK I have checked the central heating system for any leaks the last time the engineer called he said that there was a lot of air in the expansion vessel but there was nothing wrong with it but i still have the problem I have to pressure rise the boiler every two to three days

David Richards, March 2008

if you are losing pressure regularly it can only be through a leak or the expansion vessel.To determine whether you have a leak pressurise your system to 1.5 bar and leave overnight but do NOT USE THE BOILER during this period.If the pressure is still the same the next day then your system is watertight as the slightest of leaks will lower the pressure. lower the pressure back to 1 bar(drain water via a radiator)This would then tell me it is your pressure vessel which must be losing its charge of air and would explain the pressure drop

jimmy, March 2008