Our hot water pump went recently and the bloke who replaced it said we
had a lot of gunk in the system. The radiators still get hot all over
but there is a lot of black sludge about. He quoted £450 to clean the
system out with some sort of acid which I understand from a plumber
friend is a reasonable price for this labour intensive job. However a
few years ago when we had the boiler replaced the bloke who did it
said there was a problem with our radiators and he couldn't degunk???
I fancy having a go at cleaning the system out myself. I want to know
how to go about it. I understand you can buy stuff at the local DIY
store for this job but how do I go about things.
Where do I put the stuff in? Expansion tank??
What do I need to turn off to drain the system? Expansion tank fill
valve how about the cold water tank fill valve?
I will be draining the system from a valve on a radiator just by the
front door, do I need to drain the hot water system aswell.
I presume I need to turn the boiler off throughout the drain?
Should I expect leaks from previously gunked up joins?
Genral advice aprreciated. Thanks in advance.
Simple DIY guide to cleansing a CH system follows.
First, drain the system. You could refill and drain again immediately,
which will clear some of the gunk.
Now take each radiator off in turn - close down the valves at each end
of the radiator first. And be aware that you WILL get some black gunk
coming out of the radiator as you attempt to move it - so pull back
any carpets or whatever BEFORE you undo the valves. I can't stress
this enough - if allowed to contact carpet material that gunk is there
Plug the ends of the radiator, turn radiator upside down (this keeps
the gunk in the radiator whilst you navigate your way outside) and
take into back garden. Bolt garden hose on one end and let it have a
good dose of mains water pressure. You will get a shedload of gunk out
so don't do this on your prize patio or SWMBO will withdraw your
marital rites for an indefinite period of time ;)
You can then put the hose on the other end to squirt in the opposite
Once you've done the rads (and opened the valves again), refill the
system (no inhibitor) and pump it around a bit (boiler off, thermostat
high). Try closing off all but one radiator in turn, so that that
particular radiator circuit gets a good flow. Then drain system again.
Last step can be repeated a couple of times for good measure. There
will be some gunk in the pipework which will benefit from this.
Then refill, including inhibitor.
By this time and at this time of year you and your loved ones will be
freezing.....best to leave this job until spring if you can..... :)
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With a system as gunked as yours sounds to be, I would certainly go
for the clean the radiators individually method that PoP describes.
I'd add acouple of things to the procedure though.
While each radiator is off the wall open each valve and allow some
water to flush out. I generally use cat litter trays from the
supermarket under each valve - right height and will take a lot of
water. Be a little careful to avoid staining anything. This
approach flushes most of the crud out of the pipework.
Once you have reassembled the system, If you are willing to do a
little plumbing you can put a strainer on the return pipe to the
boiler. Fit a full bore isolating valve either side of it such as a
lever ball valve. As the system runs you then trap any circulating
debris and can empty it once in a while without draining.
Another good idea, once you have the system flushed is to put in a
flushing agent and run the system hot for a few hours. Then drain
once more, flush (no need to remove radiators) and refill, adding
To email, substitute .nospam with .gl
From personal experience, I wouldn't even attempt to remove any of the
radiators. Drain the system at the lowest point - there may also be a drain
valve on the boiler. Switch the boiler off and leave the water supply on to
the header tank, then with all radiator valves open, let it run until clear
(or as clear as possible). Then turn off the mains supply to the header
tank, either by the stop cock or tying up the valve. Let the system drain
fully. Introduce some suitable cleaner (eg Fernox) into the header tank,
close the drain valves, turn on the water supply and allow the system to
fill. Run for a few days, or according to the instructions. Then flush and
drain the system again, then fill with inhibitor (Fernox again possibly).
It shouldn't be necessary to drain the secondary (hot water).
The whole procedure will take you several hours (you will need to bleed all
radiators several times for instance), spread over a few days, but you
shouldn't be deprived of heating for more than a hour or two. My system is
almost 32 years old and still economically provides heating and hot water.
It's even cheaper since I ditched the useless British Gas so-called 'service
contract', whose solution to my last problem (knocking) was to offer me a
new boiler for £2000. Solved the problem myself for less than £30.
This approach will work if the system is not too badly sludged. On
one that is, it won't - I have the tee-shirt from attempting it with a
friend's system which had not been properly looked after.
Despite very thorough flushing and circulating chemical twice, the
radiators were not cleared. The problem is that the path from the
header tank to the drain cock did not go via any radiators so there
was nothing to fluch them through - no exit path either.
In the end, the only way was to take all the radiators outside. They
were loaded with sludge. After that was flushed out, a third dose of
chemical cleaner removed what was left.
To email, substitute .nospam with .gl
£450 seems a lot to flush a system, if that is what he was quoting on.
That's 3 days labour! He may have been quoting to remove each radiator and
flush them outside using a hose.
You do not need to worry about your hot water system, draining it etc,
provided it is indirect, which i would think it is.
Turn off the expansion type fill valve and switch the boiler off. Drain it
down through the drain cock, opening radiator bleed screws to let the air
Once it is drained down, close off the bleed valves and fill the system up
again. Repeat this draining and filling a few times until the water you are
daining off seems to run pretty clear.
Then, add a bottle or two of system cleanser to the header tank and fill
back up again. Run the system as normal for a couple of weeks then go
through all the draining and filling again, but this time add an
inhibitor/protector for the final fill.
You might get the odd leak but if it's gonna leak, it's gonna leak.
Hope that helps
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