2 luke warm radiators

[GrahamGerrard]

We have 2 luke warm radiators, the flow pipes are hot up to the radiators and i have checked the therm valves and they seem ok. I have bled the radiators. I have taken one of the radiators off and "flushed" it through with a jet wash and got a constant flow of pretty clean water after a lot of black stuff!!!but still no good.
When the radiator was off i opened both valves and they both leaked, i am not a plumber, but always thought myself to be logical and water flow is logical!!! (i thought) can anyone help

 

[jackthom]

When you opened the valves with the radiator removed did you get a strong jet of water out of each or just a trickle.

You should have placed a bucket under each valve in turn and allowed a good strong jet to almost half fill it. That would confirm the pipes weren't blocked and could even help remove any partial blockage.

 

[Hugh Jaleak]

Id try shutting all the rad's off bar one affected rad. If this then gets hot, try the other. This allows full flow from the pump to be pushed into one rad, sometimes shifts a blockage or air lock. If both now get hot, turn rest back on. If these 2 go cold again system likely needs balancing.

If this doesnt work it could possibly be a blockage or air lock in the return pipes.