On 2007-06-14 18:06:57 +0100, "John" said:

Two radiators are getting sluggish. The last time I removed one for
decorating I checked the flow - There was a good flow out of the "return"
but a poor flow from the "flow" pipe.

The pipes are behind the plasterboard (wallpapered only last year) and in
the case of the other - the pipes run under a laminate floor. I am therefore
keen to try a cleaner - and was thinking that if I turn off all the other
radiators it should maximise the effect on the blocked pipes.

Any comments - any suggestions? Do all cleaners need to be thoroughly
flushed out? Are some better than others?. I have tried using mains water
pressure to improve the flow - without success.

I have a system of similar age and design. By the age, I suspect that
yours is open vented as mine was. I had always been very particular
about making sure that the system was regularly dosed with a good
quality corrosion inhibitor such as Fernox or Sentinel (NOT the budget
ones because they are questionnable and a false economy for an
investment of several £k). I also took care to ensure that there was
no pumping over or sucking down of air at the header tank. These are
the main reasons as to why sludging happens in the first place.

The issue that I had was that the original installers had not done a
very good job of initial flushing and there was quite a lot of copper
swarf and other builders' crud in the system. This did tend to
reduce flow in a few places although not severely.

I took the decision to replace the old boiler with a quality condensing
model and to take the opportunity while doing so to give the system a
very good flushing and cleaning. Part of this involved changing to
a sealed system. Actually this is very easy to do and has a lot of
benefits. Essentially, the header tank and vent are removed and a
pressure vessel and filler arrangement are fitted. This could be in
the same position as the old header tank, but I fitted mine in a void
in the utility room where there is also a cold mains supply. Note
that most new boilers will work with sealed systems, older ones may not
- that would need to be checked.

Having done the new plumbing arrangements for the vessel and filler
and taken the header tank away, I fitted a strainer filter on the
return pipe to the boiler and an isolating valve either side of the
boiler.

I then took the radiators off, one at a time and out of doors for a
thorough flush with a pressure washer. Care here because sludgy water
stains indellibly. While a radiator was removed, I placed a hose
adaptor onto the valve leading to a vessel and with what is now mains
pressure applied opened the radiator valve to flush the pipework at
each radiator and each valve in turn. This method has the advantages
that there can be substantial pressure which will certainly clear out
the rubbish and that it is taken out of the system altogether and not
circulated round.

With the position of the boiler, it also meant that it was impossible
for crud to be pushed through it - only clean water.

Once that was completed, the system was put back together and refilled.
At that point a chemical cleaner is interesting to use because it
will tend to mop up residual stuff. Heavy amounts of crud would not
effectively be removed by chemical cleaner anyway, and residues etc are
simply pumped around if you just put in cleaner and run it round the
system without mechanical removal first. In any event, cleaners must
be flushed out again.

The method proved very effective and on a repeat a few weeks ago, some
three years after the original, the 20 year old system remains as clean
as a whistle.


If you didn't want to go the whole hog of going for a sealed system,
there is a way that you can still easily deliver mains pressure into it
for cleaning and flushing.
This would be to drain out the contents of the header tank and cut the
feed pipe (the one at the bottom of the tank.).. Cut the mains
supply one to the ball valve as well. Then remove the tank
temporarily. Fit a stop end to the vent pipe that is over the top of
the tank. Buy a filling loop as used for sealed systems. These are
two valves, one being non return and a length of braided hose between
them. Fit this between the mains and the feed pipe the right way
round. When you want to flush at a radiator, open the valve there
and then turn on the mains at the filling loop valve. Close and then
repeat for each radiator position. At the end, remove the filling
loop and reinstate the plumbing.