Fitting a flue

I'm fitting a flue to a new Baxi Bermuda back boiler and have a few questions.
1)The "flue outlet socket" at the top of boiler hood measures around 5.5". The instructions say that a 5" flue pipe is required.When I offer up the flue adaptor to the flue outlet socket there is (obviously) a 0.25" gap all round. Is this standard? I've read that this gap is then filled with fire cement but this gap just seems too much you would think that they would manufacture the outlet socket smaller than 5.5" diameter.
2) The holes on the boiler hood for securing the flue adaptor do not coincide with the holes on the flue adaptor. Is it Ok to drill small holes into the adaptor then screw the 3 self tapping screws?
3)When fitting the adaptor to the flue pipe and also the liner terminal do you use fire cement to 'glue' them together or is it sufficient do just push them together? If so do you smear the adaptor with fire cement then push it together or push it together then just smear the edges?
4)The boiler instructions state that I should "wrap the gas and water pipes through the brickwork and within the fireplace opening itself." What do I wrap these pipes with?
5) Is it really worth insulating the chimney or is this yet another gimick? If I don't insulate am I correct in saying that I do not need a plate at the bottom of the chimney?- all instructions I've seen are with the insulation.
Thanks in advance for any advice -I've done lots of searching but there doesn't seem to be any good websites on this subject.
Jon
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Hi Jon,
Sorry to say this, but you sound as though you don't realise the dangers of flue gases, and so I'd ask you to get some in to fit the boiler for you. You can then do the rest of the plumbing work yourself.
It also sounds as though you don't have all the bits in the correct places on the boiler flue outlets and so I think you should read the instruction book until you fully understand where everything goes.
Please don't take the chance with this crucial part of the system.
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Jonathan Curtis wrote:

You sound like your are attempting to fit a conventional flued back boiler. There is _much_ more to go wrong - perhaps lethally - than with a modern wall mounted fanned flue unit. The sort of questions you are asking make me concerned that you might not be 'competent' (see FAQ).
Regulars readers of my postings will know that I'm not one to slag off all diy activity. However I seriously suggest some help should be sought for fitting these type of boilers ( which are to be avoided if possible on several grounds).
Usually for back boilers the spigot of the flexible liner is located into the top of the draught diverter ("hood"). If the manufactuers specifiy a material for jointing than that should be used, otherwise Flue Jointing Compound is a high temperature mastic which will work well (the flue is unlikely to exceed 120C and FJC is IIRC good for more than that). Also fire cement needs serious heat to set.
Copper pipes within builders' openings are wrapped in "Denso" tape. (Ughh!) (Sort of grease loaded felt).
I may be wrong but I thought the flue securing screws were sort of like clamps/set screws?
Flue liners are finally sealed and secured in place by compacted rockwool and chicken wire.
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Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
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Thanks for the replies. I was mistaken about the adaptor it is only a small gap of slightly less than one eigth of an inch all the way round. I have found the advice on fluesystems.com useful also as there is a live on line 'chat' helpline. They say that the adaptor fits straight into the appliance hood and it is OK to drill fresh holes. All I need to do now is contemplate whether it's worth the risk....
Thanks again
Jon
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