New house, 1 cold radiator, I've run out of ideas, help!

[venton]

Moved in to bungalow recently and 1 radiator is cold. All the others get really hot when turned on. Gas system boiler, header tank in loft.
I tried balancing, turning off other radiators, increasing pump speed, but best I could get at high pump speed is a tiny bit of heat in radiator, barely noticeable heat when hand touching it.
I've run cleaner through system for two weeks and refilled.
I was convinced it must be a blocked rad or dodgy valves (which were old) so replaced with new radiator and valves at each end. The radiator filled up again ok, and I bled it.
Still the same. No heat at all, except for a warm inlet pipe when running pump full whack with others off.
Most of the other rads are copper piped but this one is black poly pipe not that makes any difference, apart from I suppose it might have kinked.
Is there anything else I can try, or do I assume blocked pipe and get the floorboards up to replace the pipe?
Thanks

 

[ShaunCorbs]

Did you test you had water running from either valve ?

 

[venton]

Did you test you had water running from either valve ?

Valves were replaced with new. On refilling system, water went in to radiator and came out of bleed screw, which means both valves allowing water to flow to some extent.

 

[ShaunCorbs]

No it does means only one might be open / flowing

Need to remove the rad and test into a buck each valve

 

[venton]

No it does means only one might be open / flowing

Need to remove the rad and test into a buck each valve

When I removed old rad after draining down, the right hand pipe (the return) did leak water for quite a while as it was slightly below drain off point. Mind you, that water could have been old water trapped behind a blockage.
I think your suggestion is the way to go. Thanks

 

[venton]

An update if anyone's interested..
Got through winter without this rad and waited till weather warmed up a bit to have another go at solving this, when heating could be off without suffering.
Found some previously removed floorboards and discovered I could get under the flooring and crawl about. Came to a dismountable joint in plastic pipe which led to the rad in question and undid it. Found pipe with crud blocking it just on the joint. Lucky. Managed to push fish tape puller through to rad and used a wet vac to suck the muck out.
All working now, so sorted for next cold season.

 

[Lou]

An update if anyone's interested..
Got through winter without this rad and waited till weather warmed up a bit to have another go at solving this, when heating could be off without suffering.
Found some previously removed floorboards and discovered I could get under the flooring and crawl about. Came to a dismountable joint in plastic pipe which led to the rad in question and undid it. Found pipe with crud blocking it just on the joint. Lucky. Managed to push fish tape puller through to rad and used a wet vac to suck the muck out.
All working now, so sorted for next cold season.

That is great that it was a simpleish fix in the end!