suddenly cold radiators

[daveaspy]

I replaced a rad and fixed a blockage in the pipe to another a few weeks ago, ran some X800 for a few hours, flushed the X800 out and refilled with some X100 added. Had the heating on a few times since then and all radiators have been nice and hot.

This week 3 radiators have decided they wont get warm. No air in them. I did notice some of the water coming out seemed a bit fizzy, is that something to do with the X100 or is there something else going on there? The 3 rads not getting warm are all in different parts of the system.

One of them is where another rad runs in parallel, tee'd off close to the cold rad - the tee'd off one runs nice and hot now (this one did have a blockage which I cleared) but even turning that one off doesnt make any difference.

I can see maybe some sludge has shifted around the system but to affect three rads at different locations at the same time seems odd, and I was hoping there wouldnt be any sludge after the X800 treatment.

Any thoughts? I guess maybe turning off every hot rad to see if it forces the cold ones to get warm?

 

[TCCHeating]

You may have airlocks in the system. Turn all rads in the house off and open one of the rads not getting hot. Turn on heating. Does the rad now get hot?

Repeat for all 3.

If each rad gets hot with all others closed then its not a blockage, then turn all other rads back on.

 

[daveaspy]

thanks - had a fiddle last night before reading the above reply. Got two of them to come to life by fiddling with the lockshields - seems all the rads on the system have the lockshield wide open which I guess wont help if there is the slightest blockage or airlock somewhere. I was amazed to find out how many of my TRVs didnt turn off the good rads when screwed right down! Thats another job that will need doing I guess

I still have one that is cold, will try and isolate every other rad including the towel rail tonight. If I bleed the cold rad there is no air but hot water does come in through the TRV to replace the bled water so that side is ok. I couldnt turn the TRV fully off to see if anything came in via the LSV side, but plenty of water came out when I opened the integrated drain off valve which leads me to another question...

I have a LSV with drain off, not too dissimilar to this (although mine is straight and not angled):
http://www.discountheating.com/images/valves/lockshield_angled_drainoff 300.jpg

does the drain off connect to the rad side of the valve so if the LSV is closed it will drain the rad? Or will it drain the pipework?