tall radiator not heating

[AJ16]

I replaced a Stelrad with a tall rad in the bathroom but it's not heating up.

The only difference in pipework is that the existing 15mm copper is extended by 800mm 10mm tails to the new rad position. New rad is full of water, Boss dual flow TRV one side and lockshield the other. The old rad had two normal valves. All other rads in the house working fine. All I can think is that the flow inlet is maybe meant to be on one particular side although the instructions didn't mention this. It did heat up initially when I opened the service vales but I think at the time that the loop to the far end of the house was turned off so I guess that squashes my dedicated inlet outlet connections theory. Any ideas on what the cause might be and what i should do to try and fix?? Should I try turning rads off?

 

[REDSAW]

have you used a bi-directional trv?

 

[AlexGas]

Is the new rad cast iron?

 

[AJ16]

Yes Boss Supreme Plus 15/10mm-
October 2012 - January 2013 tradesavers Online Brochure

 

[AJ16]

Is the new rad cast iron?

No steel tubes

 

[AlexGas]

Try to close all the other rads and keep the new one open - see what you get.

 

[AJ16]

ok I'll give it a go

 

[AJ16]

OK I fixed it today. I closed both the TRV & lockshield valve then unscrewed the flow and return pipes and put a loop across them, it heated fine showing that the pipework was ok so then I connected the flow to the lockshield & opened it right up but nothing came out of the TRV. The PTS TRV is dual flow, it was on the return side but I swapped it to the flow side and that did it. Not sure why it should make such a huge difference though.