Where is the filling loop on a Potterton HE30 combi boiler?

Further to my question, I've now repressurised the boiler - once I found the right tap under the boiler, it took a matter of seconds.
But I have two more questions for any CORGI experts:

1. As it seems so easy to do, once you find the right tap to turn, why does the manufacturer tell you to call an installer if the pressure falls below 0.5 bar?
I would guess that most people with a combi boiler suffer a loss of pressure at some point - why not make it easy for the owner to repressurise, since it does only seem to take seconds?

2. So far as I could see there was no filling loop - the two inlets where I guessed the loop should go were sealed with blanking plugs.
Would I have been able to repressurise without the filling loop in place?
If so, was it dangerous to do so?
Or perhaps the loop was there in a different place from the one I expected.

Thanks for any help you can offer.

Julian Duplain
October 2007