Do pipes from boiler have to very 15 mm?

[LadyKooKoo]

We moved house last Friday and currently have a boiler in the kitchen which is about 20 years old and two tanks in the bathroom upstairs. We are planning a kitchen extension so was always part of the plan to get a new boiler. A gas engineer came out today to disconnect the gas fire in the living room. I showed him the boiler and he said we would have to move it anyway as flues should not be under windows? He also said that all the pipework will need replacing as it is currently 8mm pipes and new boilers use 15 mm pipes and sometimes 22mm. Is this correct?

Just saw typo in title. Stupid phone!

Pigletjohn will be along shortly, but I was told last week that even 15mm isn't good enough for running more than a couple of rads and 22mm is better.

8mm pipe is called microbore. You should have 22mm from the boiler to distribution manifolds, normally situated under the floor. Then you run 8mm pipe from the manifolds to each rad. It's a system that was popular for a while because 8mm pipe can be run like cable so there's less disruption and damage when you're fitting it.

I don't know why it's gone out of favour but it's worth getting a second opinion. Try someone who has been in the trade for a long time and has experience with microbore systems.

microbore? bin it.

Quote is in at 3600. Boiler recommended is Valiant Ecotec Plus 831.