Hi Guys, I've recently had problems with my central heating system
where not all of the radiators can be switched on at the same time. A
coorgi fitter came to check and he changed the pump. He said the
system also needs flushing but for this I should contact the gas board
as it requires special equipment to do the job, as it will cost about
£350 to do. Can anyone tell me what exactly is done during the
flushing process and is £350 about right. Many thanks.
Sounds about right in terms of how much they normally fleece you for.
Sometimes they can do you for 600 quid or more. Alternatively, hire the
equipment yourself, or remove the radiators and blast them outside with a
You may find it enough just to run a flushing agent in the system for a
week, drain down and refill until the water runs clear and then refill with
inhibitor. This won't clear persistent sludge in the radiators, though.
Had the job done by British Gas who power flushed my system about two and a
half years ago.
1. About a week before the system is flushed, a cleaning chemical is
added to the system.
2. The system is then generally flushed out
3. All the radiators are then turned off and each individual radiator is
the turned on and flushed - and at the same time "tapped"
with a rubber mallet to aid the removal of scale on the radiator sides
4. The system is then again generally flushed
5. The above was then repeated until the water in the system ran clear
6. The system was then refilled with the correct inhibitor and silencing
7. The C/H expansion tank was checked and cleaned out
(The above is not a complete list)
In my case renewal of ALL the radiator valve O seals and the C/H pump was
replaced with one that ran quieter.
Again in my case, to flush out an eight rad system and a wall mounted baxi
boiler came to £460 and took a complete day to carry out.
As there were specific problems after the system flush the following was
carried out under warranty and at NO extra cost:
1. Pipework alterations in the airing cupboard to change the direction of
the way the water was pumped around the system
2. The renewal of the cast iron heat exchanger in the boiler
3. A complete re-flush of the system after these works were done and
chemicals added - all under the supervision of the
powerflush pump and chemical suppliers representative.
Was it worth it? Yes, once all the problems were sorted out (I have a
rather non-standard system fitted. This was done about thirty years ago
when the estate was built - and all the houses were the same) It has
certainly reduced my heating costs and the system is a lot better for it.
A while ago there were postings about how to clean a system out without
Also some links to a FAQ.
Depends on if you are prepared to spend a day getting wet and possibly mucky
to save the money.
AFAIK it goes something like this:
(1) Drain off some water from your CH system and add a flushing compound;
top up the water again.
(2) After the specified time (several days) drain the system and flush
through until the water runs clear. IIRC you can flush by opening the drain
tap, but not enough to drain faster than the header tank can fill. You need
to have water flowing round the system and all the radiators, so the
radiator TRVs (if you have them) should be on maximum to ensure that they
are open. The boiler thermostat should be turned off so that the boiler
doesn't heat the water you are throwing away. Keep water flowing through
until it runs clear. You should then have flushed all the moveable crap out
of the system.
(3) Turn off the water to the header tank (e.g. by tying up the float arm)
and allow the system to drain completely. Again make sure all the radiators
are drained - open the bleed valves on the upstairs ones, then later (or you
will get wet) the bleed valves on the downstairs ones until water ceases to
flow. This may take some time.
(4) One by one, using a plastic lunch box and old towels or rags to catch
the inevitable filthy water still left in the bottom of the radiators,
remove each radiator, drain the last bits of water out, take it outside and
flush repeatedly with a hose until no more black filth will come out. It
helps to have a block of wood on which to rest the threaded bit sticking out
of the radiator. Otherwise you can damage the thread on a hard surface such
as brick or concrete. Putting some water in, plugging the holes, then
shaking violently can dislodge some more crap. Hitting the radiator can also
dislodge stuff. Get an assistant - unless you have gorilla arms a double
radiator is a bit of an armful.
(5) Refit each radiator once it is clean, taking care to remake the joint to
the radiator valve; PTFE tape on the threads can help here.
(5a) Also dust behind where the radiators was, repair wallpaper, paint, and
generally do all those things that you can't do while the radiator is on the
wall. You may even wish to paint the back of the radiator. Enjoy.
(6) Take this opportunity to clean out the header tank.
(7) Refill the system and check all is well, and that all radiators are
heating up O.K. and you have no leaks or airlocks. Once you are satisfied
that all is perfect, drain some water out of the system, add corrosion
inhibitor and top up again.
Bound to have missed out stuff, but as you can see this is a major mission
for more than a couple of radiators.
Takes a lot of labour and hassle.
This is why contractors power flush instead.
There is also less risk of spilling half a pint of filthy black iron-laden
water on the best Wilton Shag Pile.
Also less risk of taking a radiator off and having problems (e.g. leaks)
Also avoids the problem of not being able to remove a radiator because the
threads are siezed up.
I had a quick Google for power flush hire but without much luck - you can
probably hire the kit to DIY which is a good yardstick for the quoted price.
A fun job if you do it yourself, but do it soon - or you will be cold in the
house and even colder outside playing with a hosepipe.
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