Erratic radiator

[Stillworking]

I have replaced a radiator with an exact duplicate re size but with the newer finned design, It is on the gravity supply and return to the hot water indirect storage tank in the loft
The old unit worked fine but was as said "old" , problem I have is that the new radiator does not seem to know which end is acting as the supply and which is the return.
One day it is red hot next day it hardly gets warm.
It has been bled and no more air comes out
Any ideas !!

 

[tryitandsee]

Do you mean that. Shouldn't it be connected to the flow at both ends, or to the return at both ends, as a 'inline' radiator.

 

[gas4you]

From your vague description I assume that this rad is on the hot water gravity circuit. This means that it will only come on when the hot water is on, although on a gravity system this would usually be when ever the boiler is on unless you have a 2 port valve on the heating circuit.

It could possibly be an airlock in the pipe work or a blockage. Does your hot water still get hot the same

 

[Stillworking]

I have replaced a radiator with an exact duplicate re size but with the newer finned design, It is on the gravity supply and return to the hot water indirect storage tank in the loft
The old unit worked fine but was as said "old" , problem I have is that the new radiator does not seem to know which end is acting as the supply and which is the return.
One day it is red hot next day it hardly gets warm.
It has been bled and no more air comes out
Any ideas !!

The radiator gets its supply from a branch off the upfeed pipe which goes from the back boiler to the top of the internal coil in the indirect tank
The return pipe from the indirect tank has a branch off it to provide the return .

The original radiator worked for years without a problem and the pipework has not been changed, the new radiator has been removed and flushed and we have proved the supply by fitting a valve onto another port on the rad and letting it flow into a bucket.

Yes the water gets hot in the storage tank and the pumped part of the system works as well

 

[Stillworking]

I have replaced a radiator with an exact duplicate re size but with the newer finned design, It is on the gravity supply and return to the hot water indirect storage tank in the loft
The old unit worked fine but was as said "old" , problem I have is that the new radiator does not seem to know which end is acting as the supply and which is the return.
One day it is red hot next day it hardly gets warm.
It has been bled and no more air comes out
Any ideas !!

The radiator gets its supply from a branch off the upfeed pipe which goes from the back boiler to the top of the internal coil in the indirect tank
The return pipe from the indirect tank has a branch off it to provide the return .

The original radiator worked for years without a problem and the pipework has not been changed, the new radiator has been removed and flushed and we have proved the supply by fitting a valve onto another port on the rad and letting it flow into a bucket.

Yes the water gets hot in the storage tank and the pumped part of the system works as well

Well heres a nugget of information for you

It would seem that modern rear entry radiators do not perform correctly on gravity fed systems due to the fact that the internal hole on the radiator pressing is a lot smaller than the inlet into which you screw the tails .

This causes a contradiction as to who supplies what, the radiator will become erratic as to whether or not it heats up.

Solution it would seem would be to fit a older type centrally fed rad such as the early Stelrad or Myson.

You live and learn !!

 

[gas4you]

Any new radiator should work on this gravity fed system. It may take longer to get hot if the other rads are on.

The flow end will be the one that comes off the pipe that is 'T' eed into the flow on the cylinder.

 

[Stillworking]

Any new radiator should work on this gravity fed system. It may take longer to get hot if the other rads are on.

The flow end will be the one that comes off the pipe that is 'T' eed into the flow on the cylinder.

Thanks for the input , but I have to try the centre option as my Plumber is at his wits end.
The info on the centre feed bit came from the Plumbing Manager of a local wholesaler who was in the trade for years and has actually come across this problem before.
I still have the old radiator so it may get a coat of white hammerite and be pressed back into service
Thanks

 

[meldrew's_mate]

If you can stand the aesthetics take the flow connection to the top of the rad, keep the return at the bottom.

It was usual to run 3/4" (22mm) pipe to gravity rads, raising the inlet will give a ittle extra "push".

Gravity rads will work on hot water OR heating OR both.

 

[tryitandsee]

Can you not create a sort of venturi effect on the downward return.

When the larger piped return from the storage cylinder pases the 15mm radiator return (22 to 15 swept reducing tee), will hopefully pull the water out (venturi effect) as it passes.

Complicated to explain, I hope you understand my drift.

Just another thought.