AGA Radiator Circulation Problem

[Monkey]

Convection Circulation?

Hi Guys,
This is my first post (noob) and I am looking for some advice (if possible) for the correct operation of a radiator (towel rail) connected to an oil-fired AGA cooker boiler which works the DHW.
To quickly explain, my wife decided she wanted a bathroom refurbishment & the builder (not a plumber) removed the existing copper radiator in the aring cupboard & fitted a new (stainless steel) towel rail - 1metre or so in height.
Problem is - it does not get warm. I used to bleed the old radiator occasionally & it worked well but when I bleed the new one it gets hot until I close the bleed valve & it goes cold again.
As it is a vented gravity/natural convection system where the radiator is connected as a heat sink between flow & return from the boiler, I am concerned about the height of the new radiator being a potential problem.
As there are not many people expert in these old systems (me included) I thought I would ask your advice before getting the builder back to sort it out as I don't think he will have a clue.
I would be really grateful if somebody could help.​

 

[justlead1]

Hi Is the towel rail a floor above the boiler or same floor?

 

[Monkey]

Hi Justlead , thanks for replying.
The towel rail is fitted on the floor above the boiler. The AGA is in the kitchen on the ground floor & the towel rail is directly above.

 

[justlead1]

Hi. Unless there is a problem with the pipe work it may well be a bit of air in pipes supplying towel rail. Try turning off one of the valves on towel rail and bleed from air valve the repeat with other valve off.

 

[Monkey]

Tried bleeding with valves closed alternately as you advised, no obvious air came out (only water).
Radiator got hot during the bleeding process but cooled down again afterwards as it did before.
There is no problem with the temperature of the DHW so I assume it must be a problem with the way the radiator is piped into the system. There are two large pipes (@ 22mm) from the AGA but the pipes to the radiator are standard 15mm copper pipes. Not sure how rising hot water is likely to flow through the radiator if these smaller pipes increase the resistance in the system. Aga produces about 70-90 galls. of hot water per day & AGA/Rayburn say its possible to run a small radiator if DHW usage is not high so it ought to work but I can't find any diagrams of where the radiator is tapped into the system. Suppose its a case of trying to find someone who might know.