problem with two rads

[hotncold]

have a problem with two rads that branch off the main circuit. I replaced them both about a year ago, they worked OK then.
Recently noticed they were getting less hot and now they are stone cold.
Have taken the rads off and opened each valve in turn-the water gushes out. water does'nt gush out so fast if the system is on, presume because the water is being shared with the rest of the system?
it's a vented system (S plan), (in a flat), no trvs and I suspect a 1 pipe system but difficult to tell because all pipework buried in concrete.
would be grateful for any ideas.

 

[Goldspoon]

Have you tried switching all the other rads off to see if the two get hot?

 

[hotncold]

Yes, I have tried that one, no difference.

 

[Gas2Air]

You replaced the rads as you said? Why? Did you cut into and repipe any existing pipework?

 

[hotncold]

The old rads looked tatty and I was doing up the two rooms in question.
No alterations to pipework.
Just a thought, would it be worth fitting a piece of copper pipe between the two rad valves to try to get the flow going, would that be less resistance that having a rad there?

 

[Bahco]

Read post 8 FAQs

 

[hotncold]

thanks Bahco
I can tick most of those points, I've tried just about everything. Looks like I'll have to check again.