Well I had nPower out today to quote me for a system. At the moment I have
an old Thorn M56, and a h/w cylinder, gravity fed system.

For initial ease of things, I was thinking about dumping the h/w cylinder
and whacking in a combi. However, the chap for nPower, who was actually a
technical person, rather than a normal sales bod (been drafted in to cover
the massive demand), suggested that given the house is classed as 6 bed, but
only with 1 bathroom (currently), that I would be better off installing a
system boiler and a pressurised system. 100 year old semi, now with cavity
wall insulation, PVCu d/g sash to the rear of the properly, wooden d/g sash
to the front, loft insulation for the rear, and roof insulation soon to be
installed for the front two 2nd floor rooms.

This would mean:
- new boiler
- new pressurised water cylinder
- my two header tanks could be removed from the loft

He also suggested TVRs on all rads (seems logical), but suggested that as
the system would now be pressurised, rather than gravity fed there could be
an issue with valves leaking.

I am not sure of the age of the system, apart from a sticky label on the
boiler saying "Fernox installed Jul 86". So if I assumed the everything in
the system was that age, then it would not seem unreasonable to replace the
valves/fit TVRs, however nPower do this for £40/rad (I have 14 rads
currently), so that adds an extra £680 to the bill - ouch!

Given the price (around £2400 - not including valve changes) I have got for
a combi from nPower (this included their £400 to match the government
scheme), but not the actual scrappage money/voucher which I need to apply
for, I would imagine I could do a pressurised unvented system for about the
same money. nPower think their quote would be about double, as they price
each item with a "standard install" cost, so the cost remains the same if
they are in and out in a day, or stuck with a pig of a job which takes them
a week or two....

SE boiler: £800-£1000
Unvented indirect cylinder: £610
Timer: £130 (most expensive I can find in screwfix cat)

I am hoping I could do most of the work myself, and just get a local chap to
give me the green light (fitting things like the flue to apply with all
appropriate regs, etc) and to do the actual gas supply work. If not, then I
might have to pay to have the boiler fitted and plumbed up, but that should
probably only be a days work.

Is there anything fundamentally wrong with my logic? I would be new to
plumbing, but my father did his house (whole boiler install, etc), so I
would have a suitable mentor, but the initially install would primarily just
moving a few pipes to fit the boiler, and then a subsequent job would be to
re-route the h/w pipes to the bathroom and toilet upsets as they seem to
take a rather indirect route, but that would be done with the bathroom was
redone.

Thanks,
Matt