Why don't plumbers want to flush out my system?

[Ripeberry]

Yesterday had the heating on for the first time since April and some of the upstairs radiators are not getting warm and a couple are stone cold.
Tried bleeding out the air, but just black water comes out and one of the supply pipes is hot at the bottom and cold further up.
There must be some severe blockages in there somewhere.
Rang about 6 diff plumbers and they said they would get back to me and no-one has.
Maybe they are run off their feet with other peoples boiler probs.
But i was wondering, is this a job that can be done DIY or does it need a professional.
Has anyone had a system flush done before?
Thanks
AB

def a job for professionals i would think. do you know anyone that could recommend one to you?

i sympathise, i too have boiler woes

I think it's quite a big job - we have same problem, our attic bedroom radiators don't get hot. Thanks heavens for electric blankets! We had British Gas chappie come out to fix boiler and he said a power flush of system would be £800, but they'd do it free if we had a new boiler installed

Just had a call from a Plumber....amazing!
He said it would cost £380 to get it done (not sure if it incl of VAT), will have to check.
He did mention British Gas was expensive but £800!! that is a bit steep!
Just waiting for our own local Plumber to call and i'll see what he says and maybe try and play the two off each other and get a discount...worth a try?
AB