I have had the worcester greenstar 24i junior boiler installed for about 6 years, but now if i have the temperature control on the bioler on number 3 or lower the pressure gauge rises from 1 bar to just the start of the red zone. if i turn it any higher than 3 the gauge goes well into the red zone, after the boiler has been switch off and cooled down the pressure is well under 1 bar so i have to refill it and start again, can anyone advise me thanks.w