Had a quote to get my boiler upgraded recently. I've got a 15 year old 30kW combi boiler that's done me proud, but as it's only about 60% efficient (or it was when new) and new condensing boilers are 90% or better I'm changing it for a new one, same wattage and again combi. It's been sucking gas from a 15mm pipe all along and the fitter thinks I need to upgrade to a 22mm pipe which, surprise surprise, is a lot more costly and I need to change the pipe running from front to back of the house.

As it's the same wattage output, and as it's supposed to use less gas than the old one, why the need for a 22mm pipe run? Is this a genuine requirement or am I being done?

fraid its in the regs, about pressure drop in the pipe on full song. Nearly all need 22mm pipe feed.

That said, mines on 15mm, but it takes a cowboy to do that

Look on the bright side, you can always get another quote!

how many meters need upgrading and how much extra is it?

Well the pipe run is only about 8 meters and I'd do it myself if it really is necessary, but it's the disruption it would cause that'd be a pain in the rear...

Was tempted to swap the boilers round myself too, but it'd be a pain when I come to sell the house with no corgi certificate. I'm sure someone'll do it for me without changing the pipe and do me a corgi, if that's not a real issue.

Pipe may well not need to be bigger if calculated with a gas pipe calculator BUT CORGI do stipulate that the pipework should be 22mm up 'til the last metre.
So...
anyone filling in the Benchmark and putting their reg no. on it would want you to upsize that pipe....

All the people who quoted for my replacement said had to upgrade to 22mm, including the firm who got the job.

In the end they said it all depended on the pressure drop at full flow and my old pipe (3/4 steel I think) was within limits so they didn't replace. This was a relief cos the proposed new pipe would have been surface mounted round tricky corners etc.

This was reputable firm and issued Corgi Cert no trouble (well they would wouldn't they ? )

The same old pipe also feeds the hob unit and there is no noticeable drop in flame height when tyhe boiler kicks in.

i should point out that when my boiler lights up, the gas fire in the front room dips for a moment. ISTR a kink last time i was under the floor, too late now as its all tiled! So pipe sizing really can affect performance.

Hmm, might be a necessity then. I did discover something last night though - the pipe entering the house is 22mm, it's probably 22mm till it diverts to the cooker and boiler. Will have to find out where that is and go from there.

Thanks folks!

do all the hard work mount etc, then neatly lay all the pipe work and electrics (if nessacery) then pay some one to finish off, ie gas man to connect pipes, sparky to fit electrics. i did this last year, thou a mate helped with wiring as he does it for living, but i fitted boiler and got a gas man to connect up, cost me about 50 quid i think! snake