Plumbing question: awkward radiators

[Nice But Dim]

I have recently moved into a new home and am trying to work out why two of the radiators in the property only get tepid at best.

The 2 rads are both fed by 15mm copper pipe into double panel radiators which are around 10 years old with TRVs and lockshields (but no drainage points) the diagram below shows the layout. As you can see the rads take a direct feed from the pump and then bizarrely go upwards into the ceiling and across the lounge and down.

So far I have removed Radiator 2 and flushed it thoroughly - there was some sludge but not a huge amount that would significantly restrict the flow. Checked that both the TRV and the lockshield are not blocked- refitted, filled and bled and its made no difference.

I was hoping that the rads would be full of sludge and hence restrict the flow into no getting hot but this does not seem to be the case. There is no drainage point currently fitted. I have tried to balance the system - but not made any difference. I have turned off all other rads in the house in an attempt to direct all the flow into these 2 rads - again they only get warm at best and not roasting like all the others in the house. Digital thermometer shown other house rads at 45 deg C - these at best hit 30 C

What diagnosis would you provide ? is it possible that all the return pipes are sludged up and restricting flow ?

[Nice But Dim]

Thanks for your help so far.... Just been to check the pipes in the ceiling and apart from a pair of very old what I presume are isolation values there are no air vents.

If this is the case I should install some bottle valves to try and remove the air ?

g7jtk said:

I agree. Partially airlocked

[Nice But Dim]

Every day is a school day

So what is the bleeding etiquette ? With CH pump on or off ?

Dogwatch said:

Yup. Just where you need them!

[Nice But Dim]

UPDATE : sadly opening the bleed valves shown in the picture released no air and only water in both inlet and outlet.

one thing I did not mention before - after flushing the rad and then refitiing and subsequent bleeding it did get as hot as the other rads in the house so clearly enough flow was at that time getting to the radiator whilt the lockshield end was off. However once the rad was full and the lockshield end opened it only ever returned to warm as before.

So either there is insufficent flow to the radiators or the return pipe is gunked up and inhibiting flow ?

[Nice But Dim]

Update: thanks to all those who kindly replied

I balanced the whole system properly and now we have hot radiators everywhere - thank you