Radiator maintenance

Hi,
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.
TIA
Tim
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In an earlier contribution to this discussion,

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?
--
Cheers,
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wrote:

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 Alphi-11.
My solution was to drain water into a plastic fermenting bucket to begin with.
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 concentration.
.andy
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On 6 Mar 2004 07:54:41 -0800, snipped-for-privacy@inscrutable.plus.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 dictates it.
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 above.
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.
.andy
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