Would you expect to be able to drain down the radiators while keeping the hot water side pressurised and running on a modern unvented system? (ie system boiler and separate cylinder, not a combi)
The installer fitted a lever valve on the "CH Flow" pipe but not on the "CH Return" and I'm not sure why you'd have one without the other.
Unlikely, as the S/Y valve(s) are rarely 100% watertight.
Yup. The CH primary side only passes through the indirect coil of the cylinder, but otherwise has no connection to it. The DHW is self contained with its own expansion vessel.
Obviously you would lose the ability to reheat the cylinder with the boiler, but if you have an immersion heater, then that will still work.
Sometimes a valve is fitted somewhere to allow the balancing the flow split between the CH and the DHW in case you wanted to ever run them at the same time.
I agree with you, but I think the answer to the OP's question is not 'yup' but 'nah'. Heating the water hot with an immersion is probably not quite what he had in mind with " keeping the hot water side pressurised and running ".
Yes I meant hot water heated by the boiler while radiators drained. That's a pain. We have a tiny leak in a really awkward-to-get-at radiator feed pipe joint. If I have a go at resoldering it and fail I guess we'd be on immersion h/w until I can get the installer back. The system is less than a year old and he seems to be covid-isolating to the point of ignoring my texts, emails and voicemails.
Thanks anyway.
Resoldering the joint won't take very long but is only possible if there is no water in the pipe.
You need to be able to isolate both the CH flow *and* return if you want to continue to heat the DHW with the boiler.
Can you get at the CH return pipe to fit an isolator valve in it? (preferably a full bore quarter-turn lever valve with compression fittings).
If you de-pressurise the system and manually turn off all the radiators you should be able to cut the pipe without getting much of a flood (but have a wet-n-dry vacuum handy just in case).
Once you have that in place you'll be able to work on the CH at your leisure.
Rather than go for the full drain and fix at this stage, is it the kind of leak you could plug with some two part plumbing repair putty as a temporary fix? (its an epoxy based stiff putty type stuff, you mix it up and apply where required. It will stick to wet pipes. It sets in 5 mins.
e.g:
No. As your valves that control the flow are on one side of that only. The return or whatever is common.
If you close off water that can be heated, whatever it's in will explode.
I wondered about that but the joint is very close to the floor and wall; I'm not sure it would be easy to clean off epoxy putty all the way round to eventually solder properly. My bodge of LS-X, self-amalgamating rubber tape and two jubilee clips is working for the moment, and plumber has risen from the dead and should be here on Monday.
I had a pinhole in a heating pipe in a tight corner, by an ancient stoothing wall, which would have been a pig to drain fully or cut out without dismanting a lot of the surroundings. I got hold of some 2mm rubber sheet and cut a piece to form a bandage. A stainless steel Jubillee clip which could tighten to the correct diameter was employed to clamp the rubber in place over the hole. It's been in place for a couple of seasons without loss of system pressure. I suppose a tractor inner tube patch would be equally up to the job.
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