Does it need purging?

[ShaunCorbs]

Just a quick up date, the gas company carried out a air to gas purge although I still don't get how air would as got into the system, I would have though the valves would just shut once the pressure dropped.
Anyway it took the gas company about 5 hours for 2 men, think there is 8 heaters in total and a few need a cheery picker to get up to them. Although I think the building owners supplied that. The bill came to around £2.5k in total which I thought was crazy.

yep sounds about right

 

[Last Plumber]

I still don't get how air would as got into the system

It's more a case of the system having lost pressure.
Safety !
In a large Gas installation you need to be certain that there is no Gas air mixture within. The larger the installation the greater the risk.

If the installation has depressurised for any reason, it should be tested, purged and recommissioned.

This does not mean that air definitely entered the pipe work. It means it is unknown whether it did or didn't and therefore we should treat it as if it did.

hope this makes sense!