Daft question but here goes...
Recently had a new combi fitted and now I need to disconnect a rad for
decorating purposes. Can I drain it in the normal way i.e. just have
the CH off - drain the water from the rad - and let the system 'fill
up again' afterwards when I switch the CH back on?
I've done this many times when I had an old CH system with water tanks
etc. Just not sure about this combi lark.
The difference you are experiencing has nothing to do with a combi per se -
but is simply that you previously had a vented system, and now have an
unvented system - with no header tank for the primary circuit.
You can remove one radiator without draining the whole system simply by
turning off both valves* and then cracking open each union between the valve
and rad, and draining the water into a suitable container. You can continue
to use the system with this one rad out.
The main difference is that when you put it back, you will have to
re-pressurise the system and you won't be able to re-use the water which was
in the removed rad **(which you could previously have poured back into the
header tank) and will thus dilute the inhibitor a bit.
* if your system has been balanced, count the number of turns required to
close the lockshield so that you can put it back to the same position
** unless it has a removeable plug at the opposite end from the bleed
screw - in which case you *may* be able to re-fill it after connecting it up
and before opening the valves. Has anyone tried this - or any other method
of getting "inhibited" water back into a sealed system?
Yes, but not that way.
For my workshop circuit, which is isolated from the house one and
connects via a heat exchanger, I have an antifreeze inhibitor.
This is fairly expensive since it needs to go in at about 30% of the
total volume - IIRC I have 4 or 5 5 litre containers of Fernox
My solution was to drain water into a plastic fermenting bucket to
I then bought a cheap pressurised garden sprayer (the kind with hose
and lance). The aluminium lance will fit and seal into an 8mm
compression fitting, so I made up an adaptor consisting of
8mm compression coupler --> 8mm tube --> 8x15mm solder reducer
-->15mm tube --> washing machine tap.
The procedure is to fill the sprayer with the water to be returned,
and with the WMC valve closed, pump it up quite hard.
Connect the WMC valve to the filling loop hose and thence the system.
Open the valve at the filling point and the WMC valve.
This will drive the water in. Pump as required to maintain flow.
Add more water and repeat procedure.
With the medium sized sprayer, there is enough pressure to pressurise
the system up to more than 2 bar, although a bit of topping up from
the mains may be needed. Obviously bleed off any air.
For single radiator removals, I tend to keep a tube of the gel stuff
and pump in a couple of squirts before refilling to maintain the
To email, substitute .nospam with .gl
On 6 Mar 2004 07:54:41 -0800, email@example.com (Tim) wrote:
It's not really directly a function of it being a combi, rather
whether or not the CH system is now pressurised.
Typically, combi based systems are sealed and pressurised, but there's
nothing apart from the manufacturer's installation requirement that
If you don't have a small header tank, then somewhere there will be a
filling loop consisting of a tap on the mains water supply, a flexible
hose and a valved connection onto the system with non return valve.
You *may* be able to just turn off the radiator valves tightly (noting
the position of the lockshield valve with a pencil, and then release
the pressure in that radiator via the vent. If it's turned off OK,
very little water will come out and any drips will stop.
You can keep the CH running in this scenario.
If they do, then you are OK to proceed with undoing the valve unions.
Use something like a cat litter tray under the unions as you undo
them. Beware that CH water contains iron salts, especially if there's
any sludging and it will indellibly stain.
If you can't shut off the valves completely, then you will need to
release the pressure from and drain the system to at least below the
radiator. There should be a drain cock somewhere. This time, the CH
has to go off. Drain as you have in the past and remove radiator as
For refilling, use the filling loop and look at the pressure gauge.
The normal recommendation is 1 to 1.5 bar, but refer to the boiler
instructions. Fill to a bit over this and vent the radiators, then
add more water and so on.
If you have had to drain or if it hasn't been done, add some
corrosion inhibitor. If you are OK with plumbing, put in a tee with
a branch pointing vertically upwards at a convenient point upstairs.
On the end, fit a compression type end stop. You can use this to
introduce liquid inhibitors.
Alternatively, there are gel inhibitors that come in a cartridge that
fits a mastic gun. There is a fitting that will go into a radiator
airt vent. Don't follow the instructions to inject against the
system pressure, but rather go to your empty radiator and inject the
stuff into it. Then fill with water as before.
To email, substitute .nospam with .gl
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