Thankyou for your helpful responses. Please forgive my followup
questions - they will probably sound really stupid to those who have a
plumbing background - however I am learning by doing, and learning
fast!!! So here goes....

1) When we flushed through the system (weve done this about 4 or 5
times now) the water now runs clear. Where would the blockage be
occuring if it appears that water is running through the system?

2) Why is it that a blockage causes the other symptoms of banging and
crashing in the system? Im afraid that something has gone wrong inside
the hot water cylinder or between the boiler and the cylinder. The
cylinder also seems to get very hot - probably overheating.

3) Do you have any instructions as to how to 'back flush' the pipes.
Would I have to connect a hose pipe and flush through mains water?

4) How would I collect the water with inhibitor in it?

5) Would there be any point in changing the pump even though it sounds
like its working?

6) Should we just bow our heads to the inevitable and pay out for the
powerflush as first advised?

Again, all advice very gratefully received.

Coldtoes.

Hi,

I can't claim to be much of a plumber at all, and certainly not a
heating engineer, but I did suffer from a problematic heating system in
a flat I lived in a few years back.

We also had the alarming boiler noise which you describe and cold
spots. After a bit of research and internet posting I discovered that
the noise is usually caused by a buildup of sludge, scale or oxide on
the heat exchanger in the boiler. This is a fairly vital part of the
boiler which transfers heat from the gas burners to the water as it's
pumped through. If the water-side of the exchanger gets coated in crap
then it doesn't conduct the heat very efficiently. Because the heat
from the burners isn't getting carried away as fast as it should bits
get overheated and expand that shouldn't expand. That's what can cause
the clanking and banging. I tried using various cleaners, desludgers
and descalers. The only one that did the trick was Fernox DS40 which is
a particularly aggressive one. It dissolves just about anything in its
path. Because of this you have to be aware that it can cause elderly
systems to spring leaks (or at least reveal leaks which had previously
been plugged by sludge).

You can find some old posts on this by searching for "pentreath ds40"
in google groups.