got a baxi boiler its 6 years old,when its topped up to 1bar it only holds that pressure for number of days,and is now down to 0.5 bar,where it stays for quite a long time,its had the pressure release valve replaced by british gas about a year ago and some seals as it was leaking,no visible leaks from boiler now(was getting water on kitchen top under boiler before)any ideas why boiler wont stay on 1 bar??