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