Single cold radiator

On Mon, 7 Dec 2009 17:32:06 +0000, Tim Lamb

If the rad valves are both working, a single cold rad can be caused by the circuit being 'unbalanced' ie, the other rads are 'stealing' all the flow. If you reduce the flow through some of the other rads by partially closing their lockshield valves, hot water will now pass through the cold rad.
David
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David J wrote:

No! Don't do that, shut the other non lockshield valves off on all other rads, then all the available flow goes through the cold rad. My system is like that, even though it is fed from a normal boiler. My system is a pig to get up and running again after a drain down because of all the loops in it and this is what I do to get it up and running again.
Dave
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SNIP
For lots of fun it is possible (with experience) to have a replacement valve ready, enclose the whole thing in a stout polythene bag and a seriously decent cotton soak sheet. With both hands inside the bag working VERY quickly you hold the old valve in place, remove the nuts, whip the old valve out of the way and have the new one in place before more than a cupfull of water is lost. Takes practice, confidence and even more confidence, but it does avoid draining down and creating all sorts of airlocks afterwards. Do make sure before you try this that the threads on the old and the new valves are identical. Some faint hearts plug the outlet and the vent at the feed and expansion tank before doing this. A kit called a plumbers mate consisting of two tapered rubber plugs is available for such a task
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cynic wrote:

Explained this to a mate once, when he needed to introduce a service valve and a tee into an existing set of rad tails. Vented system, not too much head etc. He said he understood what to do. Anyway, I was working on something elsewhere in his house and heard a "scream", went back to find a new valve assembly in place, but black iron stained water all him, and all over the place including the ceiling! I said I would do the next one. Pipe cutter until almost through - wiggle of the tail to snap it off and thumb in over the pipe end - then quick swap for the waiting valve - push down with one hand while doing up the compression nut a bit to quench most of the flow, before giving it is final tighten. Total water lost; about a cup full.
While watching me he commented that I had pre-assembled the compression joint first! (he had uncovered and recovered the pipe to place first the backnut, then the olive, and then the valve over the pipe, and also forgot to turn the valve off first!

Well worth having, but a carrot can work if you don't have those!
--
Cheers,

John.

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larkim wrote:

Don't bee too sure. You will struggle to bleed a system while the pump is running.

I can't answer that, cos I have no experience of TRV's
Dave
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OK, but I can conclude that the radiator itself isn't full of air (which I know is the first thought for a cold radiator).
Matt
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larkim wrote:

Have you tried my method of shutting down all the other radiators and running the heating through just this one?
Dave
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