Drain central heating - leave water in rads?

[EdTurtle]

Hi, i have some truly shocking radiator tails (pics to follow if anyone is interested?!) that i want to replace with chrome pipe - to attach to a towel rail. I have a baxi back boiler with gravity system.

I have two choices in so far as I can tell (correct me if I'm wrong please)

1) Bung the tank in the loft, cut the pipes under the floor, position new pipes (chrome)with a 90deg elbow, and work quickly!

2) Drain the heating down, then the same thing, but with the luxury of a bit more time.

I'm not hugely confident with this, so i thought i'd rule out option one, and drain the system down. Couple of questions about this:

Is this better than a vacuum and quick job, in terms of applying compound sealer to dry pipes v wet etc?

If i drain the system down, can i close off all rads and just drain the pipes, or am i asking for trouble with airlocks or similar?

Will I need new inhibitor if i only drain the pipes and not the who system?

I have auto bleed valves on all the radiators, does this cause any issues anywhere?

Is refilling any easier/harder with a full system drain compared to a partial drain?

I have one two port valve (c-plan system), what do i need to do with this on the draining/refilling please?

Thanks very much

 

[Daveydub]

Is it a pair of 15mm pipes feeding only the one radiator?
If so, you could air-lock it, check that flow is stopped (or near enough) and stick a pair of ballofix on with a tub underneath.
Before you do, turn ballofix to off position, put nut & olive on a spare bit of pipe, wipe compound on olive, screw ballofix on hand-tight. Olive is now in position & coated ready to whack on to existing pipe & tighten. Job now much easier. The auto vents will allow a bit of air in so water out. We don't worry because we are used to it but handy to have another pair of hands about when you are doing it. Note that base of direction arrow on valve should be put on existing pipe not the point of the arrow.

 

[EdTurtle]

I think its only one pair of pipes feeding one radiator - all I can see are two tails out of the floor, and one radiator, but dont know what its like under the floorboards yet. Would it be a problem having the ballofix under the floorboards? Also, is a ballofix: https://www.screwfix.com/p/isolating-valve-15mm-2-pack/65251 ?

If so, would full bore be better? https://www.screwfix.com/p/full-bore-isolating-valve-15mm/46860 ?

Silly question perhaps, but why would i have a spare bit of pipe in the ballofix first? Surely this would take the chrome pipe instead?

The bleed vents are all on the other radiators, not this one (in fact, there is no radiator there at the moment, the pipes coming out the floor are capped off) does this affect it in any way other than a little bit of water coming out? I have taken a few radiators off 'live' and its not a lot of water that comes out, I assume this is the same then?

Finally, whats the best way to pull the vacuum with no radiator in place, can i let the bleed vent out of another radiator, or would i best to take the vacuum off the pipes i'm working on? It'll be tricky to collect the water coming out of a vertical pipe? Once i've got the vacuum, i can cut one pipe, put the valve on, then cut the other pipe without having any problems, if i make sure i only cut one pipe at a time?

Thanks - sorry for the questions if they are obvious!

 

[EdTurtle]

https://www.screwfix.com/p/gate-valve-15mm/85316 would this be better than isolation valve, as its under the floor?

Thanks

 

[RigidRaider]

Beware - cheap gate valves don't always close fully.

 

[Daveydub]

Gate valves not great on higher presssures so stick with ballofix. Full bore is not essential where it is feeding only 1 rad, it could easily be fed with 8mm pipe so bit of restriction in valve is irrelevant.
Bung feed & vent and release water from either of your rad valves ( where the rad is removed) and you should get only a couple of pints before it stops (or reduces to a trickle). You can eaqually take water from elsewhere, a drain off, an air vent, wherever but the open ended valves are convenient to where you are working even if you need a bit of hose to divert in to a bucket
The spare bit of pipe ensures that everything is in line so that it slides easily onto your pipework. Allows you to smear paste on the olive. You remove the spare bit and then you are ready to go.