New radiator fitted cool at bottom and return pipe cool

[moray]

I have had two radiators removed in my living room, one was removed and pipes capped off under floor to free up a wall. The other one was replaced by a larger radiator 1800 x 700mm Stelrad K2 Softline. I also have a Danfoss RAS-D2 TRV with bi directional flow fitted which also came with lockshield valve. All radiators in the house are fed with 10 mm pipe, this does not appear to be an issue as I have a fairly large radiator in kitchen which gets red hot also (1000 x 600mm). All radiators are red hot in the house apart from new one fitted. It is hot at the top 1/3 and getting cooler towards bottom 2/3'rds. The flow pipe is approx 68c and the return pipe is very much cooler at 42c. The TRV is fully opened and set to correct flow direction and pin moves freely. The lockshield valve is fully open have tried in other positioned from part open to half and no difference. The plumber completed drained system at outside drain cock prior to working on it and recharged when all was fitted. I have gone around and bled all radiators, I drained two bucket fulls from new radiator as well. The system in the house is fairly well balanced as I went around and checked flow and return temps on all other radiators. Any suggestions to what it might be, plumber is coming back next week to by pass radiator by connecting a pipe to flow and return to check for good flow to rule out radiator issue. The water in the system appears clean, plumber suspects new radiator may be at fault, is that possible? I called radiator supplier and they state they have never had a new faulty radiator due to bad flow! I have a worcester bosch 240 combi boiler. I am assuming its a blocked radiator or return pipe from symptoms, the two radiators I replaced worked great.

 

[WHPES]

System out of balance or possibly an airlock somewhere.

 

[Billy Bob Bob]

i have had a plastic plug wound in to far on a stelrad before but this is extreamly rare,i assume you have tried knocking all the other rads in the house off as this may be a airlock,and also the systems balanced ?

 

[archiedale]

As whpes said, google - balancing a CH system. Lots of advice and allow enough time to do it correctly.

 

[moray]

Thanks for the comments, I really dont think its a balancing issue as I checked all rads and there is about 15c diff between flow and return, I know they say 12c, mind you I was using a temp probe which may not have best contact area. I was taking temp from where copper flow and return pipes join to chrome nut.
As for air lock could the air lock be in return pipe hence why lower part of rad stays cooler. What is the best way to get rid of an airlock in return pipe? I did turn all rads off with TRV apart from small one in bathroom as no TRV and ran system for 1 hour or so on fully temp setting on boiler but no change. What about completely draining system and recharging again. I also assume with an airlock bleeding the rad wont work as I bled two bucket fulls other day from bleed valve using a plastic jug and emptying into bucket

 

[Rickster123]

I totally agree with your situation and always sail over the information about stelrad radiators and will definitely advise to concern the radiators will have the featuring capacity.

Go sell somewhere else! These threads are ancient!

 

[glenno1]

Try turning 1 valve off on radiator then bleed then alternate to the other 1