Maximum flue length for boiler

We would like to move our bolier to the centre of the house. This will require a horizontal flue of 4 metres in distance. The plumber tells us that this is not possible and that the flue max is 2 metres. Is this true, or would anyone have other advice on how to resolve the problem ?

I am not sure about boilers, but the minimum for a stove / fire is 4 mts from start of flue.

A four metre horizontal flue is possible; It may need to be assisted by a fan. See, for example:

http://www.gasapplianceguide.co.uk/fanned_flue.htm

A general explanation of different flue types is here:

http://www.centralheating.co.uk/index/fuseaction/site.articleDetail/con_id/5170

Many plumbers have particular set-ups with which they are familiar; it is hard to get them to step out of the comfort zone; and when they do, it is hard to get them to 'RTFM'

The length depends on the boiler your using, it's possable to use twin flue on some gas boilers which in some cases give a max length of 14m. Elbows and bends reduce the overall length by 1m for each 90 and .5m for a 45 bend.

Thanks guys. Your remarks and the links are most helpful. Great help from this website.
We'll now start searching for a plumber that does rtfm!