There is one solution where the flap of pipe (copper, but also steel) is kept in a pocket, permanently: Flamco T-Plus.
These are not cheap: they cut a full-bore hole in pressurized steel pipe, irrespective of flow, with a plunger driven by a small explosive charge. There's more technology in the them beyond just a T...
The first prices I googled are 100 EUR for steel cutting 1/2" teed off 1/2", 70 EUR for copper, 1/2" into 15mm. So pricey, but entirely viable in a commercial setting where time is money, maybe less so in a diy setting.
Unless they are at the bottom of the system, you only need to partially drain down. And you can shut off the valves to each rad to minimise the draining down too.
If draining down and re-filling is a PITA, sort that first. You'll not regret doing so.
I'd always use end feed solder fittings apart from where impossible.
A full refill would be about £150-200 for the glycol. Not going there. Although much of that is in the buffer tank which is at the bottom of the system and I think isolatable. Turning the rads off as well means it's only the pipework that needs draining, so maybe that's not so bad.
I should probably work out how to repressurize it by re-injecting any fluid that does come out.
Presuming you can get the pipe dry enough to solder them if there's still water in the loop?
I have just discovered that copper pushfit is a thing. That makes it rather attractive in this kind of scenario, where you want to mess with radiator pipes but don't want ugly plastic pushfit on display. I suspect doing a snatch with pushfit and an un-drained system (perhaps even a pressurised one, although cutting under pressure might be difficult) might work in the case where even a compression wouldn't.
I was previously envious of pressfit, but it doesn't make sense for DIY as the tool is very expensive (and hiring is a faff for odd jobs) - but copper pushfit might work.
Any recommendations on system? I see the Conex Cuprofit are demountable, which might help in the inevitable case I get it wrong (and means I can practice first). The Primaflow at Wickes claim to have a release tool but every review says it doesn't work (the pictures look very similar to Masterflow so it could be related).
I seem to recall the late great Andy Hall described exactly the process that he used to capture and re-inject antifreeze rich CH water in these very pages...
He had a secondary circuit that fed his workshop - and hence went outside. I think he used a modified "pump up" garden sprayer to reload the (sealed / pressurised) loop.
("Cuprofit" fitting - sealed system, with just enough water drained to relieve the expansion vessel pressure)
IME Cuprofit are ok... I only use them in limited numbers for things like the above. (ISTR I bought a bag of 10 a decade ago, and still have most of em!)
Hmm, good idea. I think I have one of those somewhere...
One more question. Supposing I want to change the pipework to a ground floor rad. I depressurise, close the valves to the rad and disconnect them. If the system is sealed, all the water stays in the pipes. But maybe I have an air leak somewhere - some fitting is sealed when pressurised from the inside, but with the pressure let off maybe air can get in. Will that cause the system to siphon everything out from my removed rad? Or will it just amount to the run that's above my removed rad, and the ground floor room next door would be unaffected.
One example I'm thinking of is air release valves at the top of pipe runs. When depressurised will they let air *into* the system, or are they strictly release only? (I think there's often a knob to close them, but curious what happens if they aren't closed).
I *think* the siphoning would depend on where the air leak is: it would siphon all of the pipe between the removed rad and the leak, assuming the leak is higher up (if not, it would siphon out of the leak location instead). But curious to know how it goes in practice, and whether this is actually a problem.
If you turn off both rad taps, then you can remove the rad and lose no water at all.
If you then cut off one of the tails, then you will get some spillage from the pipe. If you leave a cut end open, then air will also flow into the cut end, and you will get ongoing slow loss of water. The key to working on a live system, is speed - you make a cut and get it sealed again quickly!
The lack of stored pressure, and hydraulic lock removes the torrent of water escaping from the pipe in the "oh shit the pipe has burst!" panic. It also limits the pressure to something that can be blocked by hand easily. That does depending a bit on the overall height of the property
- a three storey place might have 30' of head, which will be 1 bar/15psi of static pressure at the lowest point in the system (dynamic pressure will be less since a good hydraulic lock will reduce that dramatically when water is flowing))
If there is a path for air into the system, then water will continue to come out. A small leak as you describe is not really that relevant, since you won't be just cutting off a pipe and leaving it for weeks.
You might want to watch out if you have any automatic bleeding valves - that may allow air to suck in when there is no pressure on the "inside" if they are left in the open position. Normally they can be "closed" so they are sealed completely.
Much will depend on the pipework layout, and also if you have rads open or turned off. With all the rads turned off, you could actually drain all/most of the pipework, while still retaining most of the system water in the rads. (you would need to slacken a rad union nut near the top of the system to let air into the pipes)
In places with solid ground floors, they often do all the pipework under the first floor, and drop down to each rad. Then it is actually very difficult to fully drain the system, since even at the lowest point there are other independent low points that can't drain by gravity into the bit with the drain point (hence why some systems have drain points on most downstairs rads)
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