Replacing a radiator in a closed CH system.

[RomeoPapaKilo]

Hi,

I am a reasonably capable DIY plumber and have done most types of re-plumbing/repairs etc. However I have no experience of draining down, re-filling on combi boiler systems. Hence my query here.

I am installing a new downstairs bathroom and I need to replace the rusting radiator that is there at the moment. I have full access to the pipe work under the floor boards as there is a 3' foot gap below the floor to the foundations in which to crawl around.

The new radiator (plus TRV) is a different length to the one that is being replaced so can't just connect up to existing pipework.

Plan A.

1. Shut off both valves of all radiators, go under floor with bucket, pipe cutter and copper push-fit isolating valve (set to "off").
2. Cut through one of the pipes, expect a drench of water, push on push-fit valve.
3. Ditto with other pipe.
4. Remove old radiator, re do pipework.
5. Connect new pipework to isolation valves and open valves.
6. Bleed radiator, check combi boiler pressure and re-fill if necessary.

Plan B. Drain whole system, new radiator etc and re-fill with new rust inhibitor.

Would Plan A work? My main concern is the amount of water coming from the cut pipe before I cap it with the valve - seeing that it is a closed (ie pressurised) system?

Thoughts - better suggestions?

Thanks. Rog

[The Natural Philosopher]

This is not a lot.

Star by finding a suitable bleed point to drain down what you can. On a floor mounted boiler this is typically a hose connection somewhere at the boiler.

If its a low radiator, this is your only real option apart from freezing the pipes first.

A high level rad will of course not require a total system drain-down.

In any case the pressure wont result in much water whooshing out when its released. What causes the small flood is when air gets in to replace the water.