Draining Central Heating System

21 Apr 2004
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United Kingdom
Hi guys,

I am redoing our bathroom and have remove all the fixtures including the rad. There is going to be a towel radiator installed instead of the rad and the valves need changing. Therefore, I presume that I will need to drain the system to facilitate the removal of the valves.

I think I am pretty ok with the draining of the system, but would like some guidance on the refilling process and how to get any inhibitors back into the system.

The project may be upset by the fact that most of the older radiators upstair have bleed valves on the back of the rad, the cheap and nasty one. The previous property owner chewed all the bleed valves up and cannot really be opened. Can I isolate the radiators with dodgy bleed valves when draining/refilling the system, or is this impossible and I will have to replace these radiators aswell.

Any help very much appreciated

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Pressurised system or open vented?

You can often undo a nut on the top of modern towel rails and fill from there if its pressurised, otherwise chuck additives in the F&E tank

With the other rads:- If you cant undo the bleed valves you are not going to get the air out so they will be useless.
Undo the bleed vlaves or renew the rads
Hi Slugbabydotcom,

The system is a pressurised system. I presumed as much with the rad's upstairs, and as they are the cheap older models with the valves at the back, they cannot be replaced, so I will have to replace the rad's.


Another way of getting inhibitor into the system is with the system drained take a radiator off, turn it upside down and fill it through the rad valve connection. Then put both the rad valves on to the rad and close them off before re-connecting the rad to the system. Its a bit of a mess about but cheaper than using THIS

There should be a silver braided filling loop usually somewhere near the boiler to get the water back into the system. With the air bled out of all the rads your system pressure should be 1 - 1.5 bar for most boilers

Any probs - - - just post back
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Thanks for the info, there is indeed a filling loop under the boiler. I am going to replace the faulty rad's upstairs at the same time as draining the system. This may also make putting the inhibitor into the system easier. If I get any problems, I will drop a post.

Thanks again for your help.

Before you bin those rads (they still make Barlos like that) get a decent big brass rad vent key and file the end square, then file the outer corner off all round, so it would be pointed llike apencil if the middle were solid. That will give you a much better chance of turning the squares. You could TRY taking one of the cores round a couple of local plumbers merchants to see if they have any vents with the same thread.

Most rad key seem to have the metal missing where you need it most!

You can also grip the sides of the square with a small pointy "Mole" type wrench, or a baby adjustable spanner (v cheap type) with the ends groundso they'll go in the small gap round the square, end on.

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