So I should ditch the boiler, and install a datacentre then?

Sounds like a plan. :P

If you have an old heating system, mine is about 20yrs old, as others have said before, the economics of updating the system needs careful consideration.

Under recently revised building regulations, if you change a boiler (and it now has to be condensing unless there's really good reason why not, and that'll be changing soon too), the whole system has to be updated to current regs standard, i.e. thermostatic rad valves, timer/controller, factory insulated cylinder (if you have one), thermostat on cylinder, pipe insulation etc., and if it's like mine the cylinder vents isn't up to current spec either.

My old Potterton boiler is 100% reliable, about 65% efficient (according to SEDBUK rating), and I reckon an update would take about 12yrs to break even.

As others have said, under these circumstances insulation is the way to go. For DIY loft insulation try the Crown/Knauf Space-blanket stuff, it's plastic covered so virtually no dust, it's about 50% dearer than normal stuff but convenient.
http://www.buildingtalk.com/news/kna/kna110.html

Current building regs would start at typically 250mm thickness for loft insulation. Take care to ensure adequate loft ventilation to avoid condensation and dry rot.

My hot water is gravity, and I've improved the efficiency a lot by generous insulation of all the pipes between boiler and cylinder, also running it only once rather than twice per 24hrs. It's reduced the summertime HW-only running costs by about 25%. Also a second jacket on the (old bare copper) cylinder. I get the pipe insulation from a local Heating&Plumbing trade warehouse, costs about half the DIY stores prices.

Set the water temp thermostat as low as you can live with, saves heat loss. Too low a temp can make corrosion worse though.

Thanks Embee.

I have had a look at the website for the insulation, and think I may well sort the loft out. Can only help huh.

Will need to remove some of the loft boards (as it is half boarded) and then buy some new ones to complete the job. Should makes things nice n toasty!

Thanks for all the comments!

I have switched the heating on, but as I'm mean and have the room stat set to 17C, it's not actually kicked in yet. The loft must have 6" of insulation (I did it 12 years ago) and we have German-made double glazing with a large air gap between the panes. The boiler's a 26 year-old floor-standing 65K BTU Potterton which hasn't got any electronics in it, so it's reliable. Gas costs are difficult to gauge, as there's another system in the house too (in my mother-in-law's annexe) which seems to run most of the year round keeping her warm. Combined gas and electricity bills are staggering. Too many computers (4), tellies (5), washing machine, tumble dryer, fridges (2), freezers (2) and *lots* of lights all on at once. :cry: