Draining microbore closed system

[AWJS01]

My central heating is a closed system with a combi boiler and 7 rads all on the same floor. The pipes are 8mm microbore, which I gather is plumbed as a 'star' from a central 22mm pipe and a manifold.

I need to drain the system to change radiator valves on one rad. There's a drain cock that's a bit awkward to get to so I was planning to drain from one of the valves that I'm planning to replace.

To make this a little easier (I can only really get a tray under the valve) I was wondering if it was possible to close the valves on all the other radiators, so that I only drain the pipework rather than the rads.

When I refill the system I could then leave the air vent open on the new radiator and stand by with a bucket when the last of the air is forced out (rather than chase air around the system later on).

Is there something I'm missing here? It SEEMS like a cunning plan, but you may put me right!

Any comments appreciated!

 

[kevplumb]

big rads or small rads

 

[AWJS01]

Actually there are only 5...

One 120x60cm double
One 60x40cm double
One 90x60cm double
One 120x50cm single
One 60x60cm single

The 6th is the one that isn't currently connected/filled - it's a 4-column thing from B&Q.

Al.

 

[kevplumb]

if its only 8mm close the valve you are not changing freeze the pipe at other end tray under rad to cach the small amount of water
job done

 

[AWJS01]

I wasn't clear before - the radiator's new and currently empty, so the only water would be from the central heating pipe.

I was looking at the option of freezing the inlet pipe, but there's only about 4 inches of the 8mm pipe between the floor and the valve that I'm taking off - does that cause a problem?

The freezing kit says to freeze 7" from where you're working, but then I'm not going to be using soldered fittings - just the compression fitting on the valve.

Freezing would certainly be a lot less messing about...

 

[kevplumb]

you shouldnt have any probs 8mm freezes dead easy just wait till you hear the crack(when you try it you will know ) ang get all your gear ready beforehand

 

[AWJS01]

I'll ry the freezing option then - I suppose I can have the tray and hose standing by, so worst case scenario I end up draining via the rad by default!

One last question... I take it the freezing doesn't distort the pipe at all - I'm not about to freeze the pipe, fit a compression fitting, then find out it leaks once the plug melts?!

You've been a huge help by the way - thanks!

Al.

 

[kevplumb]

no is dosent distort the pipe but try to freeze it well away from where your working (not always possible i know)

 

[AWJS01]

I should ask though - in case I can't freeze the pipe and have to drain the system, what do you make of the idea of shutting radiators and just draining the pipework?

 

[kevplumb]

yeah no problem should work ok

 

[AWJS01]

Thanks!

 

[namsag]

No need to drain just turn off flow and return valves under boiler and release excess presure out of a bleed screw you will get anything from half pint to about 4 pints close bleed screw when water stops . This will then put a vacum into system and you will be able to remove valves and change one at a time without any other water coming out providing you don`t have a leak elsewhere on the system if air can`t get in the water can`t come out.(bit like the trick of turning a milk bottle full of water upside down with no lid on it and the water stays in). For the pro`s out there it`s just the same as using a bung kit on an open vented system and if youy can`t turn boiler isolating valves of screwing down the auto air vent cap will allow you to do same. Only occasionally will this not work and have done soldered joints on up to 22mm fittings. Sorry if this sounds like teaching your granny to suck eggs

 

[AWJS01]

Sounds like a good idea! I'm pretty sure there are no leaks in the system (solid at 1.1 bar without top up for ages) so that shouldn't be a problem. Since I'm only using compression fittings, I'm not so bothered about the odd drop of water. I'll post a follow up and let you know how it goes!

Cheers,

Al.

 

[kevplumb]

go get it floyd
be nice to the wife
shes warm now

 

[namsag]

When you initially take valve off stick a little plug of tissue into the rad tail to stop any waterdripping out