The filling loop pipe on a sealed system - is it OK to leave it connected?

Andy From Sligo

The loop pipe on a fully sealed CH system, once the system is filled to 1bar or thereabouts is the pipe supposed to be disconnected or left in situ connected up but with the taps turned off?

Am sure i saw a youtube video of a boiler engineer in the UK filling up a sealed system and was sure he said "the pipe must be disconnected by law after filling" - but over here in Ireland I have seen the loop pipe connected all the time on the systems I have seen.

What would be the reasoning anyway for it to be disconnected by law would it be so that the water from the CH system does not syphon back into the mains water system and pollute that and everyone's mains water down the street and give them legionnaires disease or whatever it is ?

John.G

The main reason for disconnection and best practice IMO is to prevent over pressurisation of the heating system resulting in the lifting of the PRV at 3 bar and in some cases like the Grant oil fired boiler at 2.5 bar, despite having 2 isol valves and normally a double NRV installed at the boiler end for legionella protection. Despite the obvious some gas fired boilers have permanent filling loopswhich one can programme to auto fill a completely daft status IMO as a slight leak will go unnoticed until your rads get pinholes. I have a 50 year old gravity OV system but I have a isol valve on the mains supply to the ballcock which I keep closed permanently, somerads are > thsn 40 years old