I get water not air, a common line of thinking, but not the right one.

If for example you have air locked in the return, then the water will still flow via the flow and viseversa.

You need to isolate one pipe and bleed any air out then isolate that pipe and bleed the other.

Hope that all make sence.

scruff

[quote author=Dave.B  link=1104676041/0#2 date=1104677591]Thanks Scruff - I see what you are saying. How do I isolate each pipe in turn? [/quote]

turn the valve off on the rad, then swop them over, i.e. close and then open the second.

For best results turn the pump and boiler off.

scruff

[quote author=Dave.B  link=1104676041/0#4 date=1104696329]Got it - thanks mate. [/quote]

Yeh   But did it work  

happy new year

scruff

Not got round to it yet

Your mrs must be patient - i changed our boiler over the christmas holiday and my mrs nagged me that when she woke up the next day she expected hot water and heating so i had to work till 4 am to get it back on

Dave i had exactly the same thing happen to me this week after adding two new rads.
The first thing you need to do is balance them.
Even after doing this i still had 1 rad that was stone cold!!

In the end i closed all the valves on the feed pipes to the rads (except the cold one)and after about 5 minutes you could hear the rad gurgling and then hey presto the rad was piping hot.

Might be worth a try. ???

Ok mate let us know how you get on

[quote author=Dave.B  link=1104676041/0#12 date=1108148112]in which case all I need to do is swap the valves to opposite sides of the radiator - right? [/quote]
wrong, imagine the radiator as a fat bit of pipework, if you turn it round, valve to opposte sides or change pipework to opposite ends, its still the same loop, might go a different way thru the rad but thats no matter.

What happens if you turn off all the other rads in the system, leaving only this one on?

all a thermostatic valve is, is a regular rad valve with a thermostatic control unit stuck on top. However you might be right in the only flows one way theory, might be just the ticket and in any case cant do any harm.

When the high level heater was removed there might have been some sh*t stuck in the pipework, if you remove the rad and open the valves do they blast water out? (this is a wet test, i.e you will get wet!)

can you connect a hose to the valve and have it blow for a few seconds to see if its actually getting water and not just letting out the "pressurised" water already there.

Will await reply to the current test first lol......

i take it you found your rad thermometers then chaddy(at the ends of your arms?)

I read a link on here the other day about balancing the rads (I think it might have been on your thread chaddy?) but all other rads in the house seem to be at a similar temp (i.e. by touch), actually they are all bloody hot to the touch - maybe that is a problem in itself.

The gunk in the pipe theory is a sound one - the original high level heater was fed by 15mm pipe, and immediately after that it branched into 8mm - I may try taking the rad off tomorrow and give that a go.

The lockshield valve does have a drain cock on it, even though it's on the first floor (split level house - i.e. upside down), but it's it such an awkward position I may not be able to get a hose on it.

I've abandoned the "all other rads off" test now, as it's been 50 minutes with no effect. Shame - it was a good idea that made a lot of sense to me.

@ Chaddy: I don't know if the plumber who fitted the system balanced the rads or not. From what I can tell, there were only 4 radiators fitted when the house was built (1985), and sometime since then someone has been in and fitted more radiators (the pipes for these are 8mm and fixed to the wall inside conduit - looks terrible, but I have more urgent aesthetic problems to sort before I do that!).
So I think the whole system is a bit of a mish-mash of different people's work. I have been here for just over a year now so it's a mystery to me really.
The only thing my plumber did was to remove one high level fan heater from the kitchen. Unfortunately, I think he was just unlucky with this.

*shakes head*

I'd have shaken my head if i'd burnt my ear too

Woo hoo!
The plumber has just been and left. I have a new towel rail in my en-suite, my ball-valve in the loft is not dripping anymore and more importantly: the radiator in question is now working again.

Only cost me £40 so Dave.B is a very happy boy indeed!

The problem was what many of you suggested: air lock in the flow pipe going to the radiator. Cured as you suggested by closing one valve and cracking the union nut at one end, then vice versa. Just didn't have the guts to do it myself!

Many thanks to everyone who offerred their advice.
Dave

I know, like I say, I'm still beaming from ear to ear.
As I mentioned earlier, he has quit the trade and is now only doing small jobs for people he knows - he is a friend of a friend, so mate's rates apply I suppose.
I'm going to spend the money I saved on a slap up curry with extra sag aloo this weekend.