Can't get one radiator hot - what can I try next?

[Brovagen]

I'm sure this sort of topic has been discussed to death & believe me, I've tried everything to resolve it, but failed...

Bosch 30CDi system boiler, S-plan with12 radiators.

All radiators heat up as expected apart from one in the kitchen. If the boiler runs for a fairly long period, the radiator will eventually get warm, but never hot enough.

The flow pipe to the TRV is hot & once opened, the entry point into the radiator is hot, but there just is no flow through the radiator & it remains cool/warm.

I took the plunge & thinking the radiator was bunged-up, I replaced it with a new radiator, but this had no effect.

The pipe on the return is cold. The lock shield is fully open and I've proved is functioning ok. ( I closed off the TRV and lock shield valve, drained the radiator and then re-filled the radiator by opening up the lock shield valve)

It's not a balancing issue. If I close off all the other radiators, this one radiator still fails to heat up correctly.

So, my question is, other than a severe blockage in the return pipe from the radiator, why may there be no flow through this one radiator?

Any suggestions welcomed...

 

[ShaunCorbs]

Remove the rad open the flow should get good flow out and do the same with the return and report back

 

[Brovagen]

Remove the rad open the flow should get good flow out and do the same with the return and report back

Thanks for the reply...

I actually did what you suggested with the original radiator and I did get good flow. I concluded a blocked radiator, which is why I ended up changing it, but, to no avail....

 

[ShaunCorbs]

Has it ever work as it might be teed into just the flow

 

[Brovagen]

Has it ever work as it might be teed into just the flow

Good question & I really don't know whether it's ever worked properly...

Are you suggesting that the installer has possibly connected the return back into the flow?
In error or by design?

 

[ShaunCorbs]

Yes taken both either from the flow eg flow and flow or both on the return eg return and return

 

[Brovagen]

Yes taken both either from the flow eg flow and flow or both on the return eg return and return

That would make sense in terms of why there's no flow, but surely that would never work!
Would that be down to poor workmanship?
without lifting a laminate floor, I can't examine the pipework...

 

[ShaunCorbs]

If it’s never worked and got good flow from both it’s likely

Can’t comment on why it’s happened

Might be easier just to re run it on the surface ?

 

[Brovagen]

If it’s never worked and got good flow from both it’s likely

Can’t comment on why it’s happened

Might be easier just to re run it on the surface ?

Thanks for the suggestion & reasoning...
Unfortunately, a surface pipe isn't possible so looks like I'll have to cut an inspection hole in the floor and have a look.
If I find anything, I'll report back.
Cheers!

 

[Brovagen]

If it’s never worked and got good flow from both it’s likely

Can’t comment on why it’s happened

Might be easier just to re run it on the surface ?

Sorry, just had another thought...
If, we assume that both the flow and return are indeed connected to either the flow or return pipe, wouldn't you expect both the flow and return pipe to be at the same temperature at the radiator?
In my case, the flow is very hot at the radiator, but the return is cold.

 

[ShaunCorbs]

Only if you pull some water from both

 

[Brovagen]

Sorry, just had another thought...
If, we assume that both the flow and return are indeed connected to either the flow or return pipe, wouldn't you expect both the flow and return pipe to be at the same temperature at the radiator?
In my case, the flow is very hot at the radiator, but the return is cold.

Only if you pull some water from both

I'm not really sure what you mean.
Are you saying that even though they could be connected to the same source pipe (flow or return), there still could be enough water draw through the radiator to generate a semblance of flow?

 

[ShaunCorbs]

Yes the water will warm as the other system water is heating

 

[John.g]

To prove once and for all that the rad tails arn't teed into the one pipe, with boiler firing normally, shut both rad valves and completely remove the rad needle vent, get a bucket and open just one valve fully and allow the water to flow into the bucket for exactly say 1 minute and measure it, do the same with the other valve, there should be a appreciable difference in the measurements if the rad connected in properly, you will have to get someone to keep the boiler pressure topped up while doing this, also put a drop of inhibitor in the system afterwards.
The above will also to remove any air pockets.

I found the above problem in a neighbours, a very long, SP rad that used to heat a fair bit more than just lukewarm but was obviously acting a bit like a one pipe system.