Why why why?

[DirksPlumbing]

Still do not understand why the filling loop had been fitted and the key left with the customer. And capping off the safety device is something I can not imagine as being advised by Worcester. If someone closes both valves it would still have protected the boiler. Whereas on a conventional boiler you will not find valves to isolate the boiler as it is open vented.
So in my opinion the guy is right. It should still vent safely to the outside.

 

[GrahamM]

Still do not understand why the filling loop had been fitted and the key left with the customer. And capping off the safety device is something I can not imagine as being advised by Worcester. If someone closes both valves it would still have protected the boiler. Whereas on a conventional boiler you will not find valves to isolate the boiler as it is open vented.
So in my opinion the guy is right. It should still vent safely to the outside.

Because it was supplied as a fully functioning, sealed combi, but installed as an open system.
It would be pointless to install a PRV pipe.

I must admit I was scratching my head at a similar system some years back and penny dropped after quite a few minutes when noticed no PRV pipe.

 

[tamz]

It would make no difference if both valves were closed and the boiler was fired up. It is still open to the atmosphere through the vent pipe which is connected where the auto airvent was. Some, 280's iiirc, had a brass plug that was removed and the vent taken from there.
The prv wasn,t needed and was blanked off and the key was usually thrown in the van for a spare.

At one time BG wouldn't pressurise an previous open system if a combi was being fitted and insisted on a full system being done. They changed that after a while to 10 bar rad valves had to be fitted (peglers etc) but eventually just fitted them to whatever as most everyone else was doing it anyway with no ill effects and they were loosing sales.
It was most likely fitted by them.

 

[Nostrum]

I've seen these and scratched my head for a few minutes too. They aren't common and when your used to seeing combis day in day out you assume it is the same as the others. The key should have been binned though to save the confusion. I wonder how long they tried filling it for though and whether or not the water coming out the overflow was a give away !