Cold radiators - totally flummoxed

dopiaza

The problem is the flow rate through the pipework to the radiator. IT IS NOT AIR IN THE RADIATOR. The microbore pipes(probably the return)(the cold one) is restricted. Try turning all the other radiators off while the heating is on. This may clear an air lock from the pipes but I suspect a blockage or kinked pipe. Best fix is to have rad repiped, preferably in 15mm.

withabix

I've got 6mm microbore. It's a pain in the bum.

There is a small dent in the microbore in our conservatory (yes, I know I'm not supposed to have a rad in there!) and it has sludged up. I can't face digging the pipe out of the wall at the moment...

Do they still use 6mm in new installations? It seems to have irtualy disappeared - only proper plumbers merchants stock it now.

thechippy

You need to have the system flushed. If done properly, it's not a problem even if you have microbore - they should also do a reverse flush. I had my microbore system flushed when I had a new boiler installed and it caused no problems..

dollydolittle_2

Thank you again everyone. I will ask them to come back and decide if we need to dig out the pipes next, or if we should try powerflushing the system first.

moonlight123_2

i had a sludged up system and got a power flush, it worked a treat and now i have no problems, i used powerflush northwest based in manchester

dollydolittle_2

Me again. Not solved this yet.

The rad in question was repiped with 11 mm plastic piping. In effect that means all the pipework to this rad is new as we changed the site of the boiler, so from the new boiler to the manifold has new piping, then new piping from the manifold to the new rad. It gives off a little more heat than before, but still only the top third gets hot. We have Fernoxed several times and have a Magnaclean.

I have arranged to talk to my plumber about this again tomorrow (he's had a busy few months apparently). Today we shut down all the other rads in the house to check again that it isn't a balancing problem. With all the other rads off, it took ages for this rad to get warm, and it didn't get any hotter than usual. I had my hand on the pipe into the thermostatic valve and hubby had his on the other pipe. My pipe barely got warm, but after a while the other pipe was very hot. Surely that is the wrong way round? (When we turned on the other rads they heated up quickly, with the pipes to the thermostatic valves getting hot first.)

Any ideas anyone? (btw, as suggested above, we checked that the valve wasn't stuck in the down position, and it wasn't and it seems very unlikely to be sludge as the other microbore piped rads from the same manifold are belting out heat.)

lovesgshp

If the outflow is getting hot, then it does seem like the thermostatic valve is stuck and the water is just bypassing the radiator. Have you also checked for air in that rad??

dollydolittle_2

Thanks for getting back so quickly - definitely no air whatsoever in that rad. The top third gets hot, not as hot as other rads in the house, but I'd be happy if I could get it to be that temp all the way down.

What else could be stuck in the valve, apart from the bit we checked following Cardew's suggestion?

lovesgshp

The valve could be faulty, it may be a good idea to get a new one and replace the existing.If you think of the ones in cars, wax type,then they can close causing a similar problem.

WhiteHorse

I also have this problem with a brand new CH system. One radiator refuses to get hot, even though all the others in the house are very hot indeed. I've bled the sytem repeatedly, checked the TRV, and even replaced it with a spare. Personally, I suspect badly laid out pipework.

The installer will be taxed about it tomorrow, so I'll post with the result.