Cold return on radiator.

[diy_dave1978]

Hi,
I'm trying to make a radiator in a living room heat up.

The flow pipe at the radiator gets very hot. Return stays cold. It's as if there is no flow through the radiator. Temperature difference is much greater than on other radiators.

The system is on 10mm pipe. I presume, but don't know, that there are manifolds under a floor somewhere. It was a gravity fed system that was changed to a combi several years ago. I don't know when the radiator last worked "properly". 3 radiators downstairs. 4 upstairs. Small house.

The valves are new. The radiator is also new (problem was there before radiator was replaced).

The system has quite clear water when draining.

I presumed this meant a blockage in the return leg to the manifold. However, yesterday I put a "wet vac" on the return, tried using a foot pump (but was scared of breaking something). Some dirty water did come out. I then gently opened the filling loop to verify water was coming out of the return pipe, and it did (into my face).

So, does the really hot flow to the radiator mean it's not a balancing issue?

Thanks.

Dave

 

[Jurassicspark]

Turn off all other radiators (except this one) and try seeing if it will warm up.

 

[terryplumb]

Does water flow freely from both valves ?

 

[diy_dave1978]

The valves are new, and the flow side pipe and side of the radiator gets hot.

I didn't check the flow side pipe for flow, given it gets red hot. Am I incorrect to assume that? There was a decent flow from the return with the filling loop open slightly.

 

[terryplumb]

Try closing all other rads off as suggested above ,if it still doesn't heat fully there is no circulation through the rad,and both flow and return need to be checked to be running freely.

 

[diy_dave1978]

I tried closing all other radiators. No change to the problematic one.

To confirm the return isn't blocked, I connected a hose to the drain off on the lockshield valve. Turned off the TRV. Let the water flow out the hose and opened the filling loop. Water continued to flow out.

I'm at a loss now. If I ever get a solution, I'll update.

Thanks for your help.

 

[terryplumb]

That hasn't proved that the other TRV side is flowing freely ?

 

[diy_dave1978]

That's correct. I'll try that if you think it's worthwhile. There is some heat from the flow side and the flow pipe itself is baking hot.

 

[terryplumb]

Yes it is worthwhile, even though the pipe is hot it doesn't mean there is FLOW. There has to be a reason that hot water in that pipe isn't flowing through the radiator ,from what you have told us the return pipe isnt blocked ,the rad valves are new and so is the rad , I assume the rad heated fully at some point in the past ,so that really only leaves the flow side to be severely restricted.

 

[diy_dave1978]

Hi,
I tried pointing the flow valve into a bowl and raising the pressure on the boiler gauge to 1 bar.

In terms of flow, there was clear water coming out but it was not fast. Hard to describe, but was projecting a couple of inches or so beyond the valve before falling to the bowl.

Dave.

 

[terryplumb]

How long did you let it run for ? With boiler electrically isolated ,Setting the pressure to 2 bar ,and maintaining it at that whilst you let water flow from valve for one full minute ,what is the result ?
What is the flow like from the lock shield valve ?