On Wed, 18 Sep 2013 10:31:45 +0100, Davidm wrote:


http://www.toolstation.com/shop/Hand...s/Radiator+Val

ve+Change+Kit/d10/sd210/p31768

http://tinyurl.com/m3jhbc4

Ah yes, I've got a couple of these, I guess I have to plug both the
feed and vent pipes at the tank.

Yep. If air can't get in, water can't get out.

The "negative pressure" of the water won't damage anything in the boiler
will it?

What "negative pressure"? Nothing is leaving the primary (or
shouldn't...) if anything does it means some thing has got in some
where. The system remains at it's static pressure determined by pure
head.

I've heard tales of people who have seen hot water cylinders collapse
when these plugs have been used on the hot water side of an open vented system and then opened a tap at the lowest point!

Well I guess there is the "pull" from the weight of water in the pipe
work below the cylinder. Which in a normal house with cylinder on
first floor and taps on ground could be could be around 8' of head or
1/4 atmosphere.

--
Cheers
Dave.