Further to my post on boiler questions earlier in the week, tonight, we tore out the old bath, after simply shutting off the supplies to the boiler / rest of the house cold feed, as advised by the good folk on here. Didn't lose a drop of water. Once the bath was out, I removed the tap block, and just fixed it back on the pipework as a temporary measure so that I could get the water back on, and evaluate what was going on with all the pipework behind the bath. It seems to have been modified at some time in the past, when a shower was added, and it's a bloody mess, so now I've got the measure of dealing with one of these combi boilers from the hot / cold water aspect, I'm going to tidy it up to new spurs to put my new push-fit flexi tap connectors onto.
As to the other part of the job that I've got roped into - replacing the rad in the bathroom - I've now had a good read up on her exact model of boiler. I managed to get the installation / technical manual off the manufacturer's website, and it all makes sense now. I have found the filler loop, and as suggested by someone in the original thread I think, it *is* permanently connected. It has been put in what was the airing cupboard before the boiler was replaced in the past. It looks as though they have just put it between what was the cold feed to the header tank, and the CH return pipe, which also passes through the cupboard. Now that I understand the principle of filling from the link provided by John Rumm, I can see that it will be a straightforward job. The pressure gauge is right on the front panel of the boiler, and it is currently a little low anyway.
Anyway, thanks for all the advice so far - it has helped no end. Hope to get the new bath plumbed in tomorow night. Hopefully, it will go as well as getting the old one out ... :-)
Arfa