sludge in the boiler & system ?

[ALMAJPJL]

I recently had a plumber around to service the boiler. He told me that the boiler was fine, but was full of sludge and that both the boiler and heating system would need to be flushed out with a quote of £645!
When I bleed the radiators the water which comes out is Gin clear! Is this because all the sediment is sat in the bottom of the radiatiors or is this a ploy to fleece me some more

 

[ALMAJPJL]

It's a Britony combi boiler/system by C & M

 

[davetheplumber]

your plumber is certainly taking the *iss. you shouldn't be paying more than about £300.