Vertical Radiator Problem

dwilden

Hi,

I've just had an ancient 500mm high radiator in an upstairs bedroom replaced by a 1800mm tall vertical radiator, but I've run into as problem in that I don't think I have enough head of water to completely purge the air out of the radiator.

To explain...My boiler is not a combi type, and the heating system has a header tank in the loft. The bedroom is also located in the loft. I believe the water in the header tank is well above the bottom of the new rad but lower than the top of the rad.

I have to bleed the radiator with the pump off as the pump is on the return to the boiler and so just sucks air into the radiator if the pump is running.When I bled it with the pump off, some air came out of the radiator, but then stopped venting air and no water came out. I'm assuming this is because the water in the rad had reached the same height as the water in the header tank?

From measurements,of the relative heights, I estimate the radiator should be 3/4 full. However when I run the heating, none of the radiator gets hot - I was hoping it would be hot up to the level of water The only think that gets hot is the pipe connected to one of the radiator valves.

Can anyone please advise:

1. The vertical radiator has two horizontal tubes, one at the top and one at the bottom, and lots of vertical tubes running between them. With this design, does the radiator have to be full of water to get any flow of water within the radiator, or should it work (with less than 100% efficiency if 3/4 full?

2. I've read that some vertical rads have flow valves within them to improve their efficiency. Not sure if mine has one, but if it did, does this mean that water will not flow in the rad if the input and return pipes were to be connected the wrong way round?

3. Its been suggested I could loosen the rad valves and tip the radiator down so as to drop the level below the header tank level, then bleed the rad and return it to the vertical.
If I did that, would the pump increase the pressure in the system enough to make water flow, or would it still be limited by the tank head pressure?

kcopp

Its not a pump issue. You need to add more pressure to the system...then bleed

mattmia2

I assume the old radiator was shorter and the top below the top of the open expansion tank?

Jamie Hall

kcopp said:

Its not a pump issue. You need to add more pressure to the system...then bleed

Well, yes, but I believe you said that the header tank was below the top of the radiuator, @dwilden ? Is the header tank vented to the atmosphere? And you said the pump is on the return?

If so, you're stuck. Depending on how the radiator is piped you'll either get little or no heat at all out of it. If both the inlet and outlet are on the bottom, you may get a little, depending on the rest of the piping. If either is on top, no flow, no heat.

mattmia2

If you could find a way to purge it to fil lit it would work but it would tend to collect all the air that ends up in the system so it would be a constant problem. A shorter radiator or converting to a diaphragm expansion tank and relief valve is the solution, assuming an open expansion tank.

JUGHNE

Could you raise the tank higher?

dwilden

Thanks for everyone who has replied.

Yes the top of the old radiator was only 600mm above the floor. The new one is approx 1900mm above the floor. Both valves are at the botton of the rad.

I'm sure the top of the tall rad is above the expansion tank, but there is no room to raise it. It is an open tank.

As well as the new radiator, I've just also had a towel rail fitted in an ensuite off the same bedroom. That one is 1000mm high and works fine, so I am sure the other rad would work if it I replace it by a shorter one.

The tall rad did have little stickers on it marked input and return (or similar) which makes me suspect there is some sort of one way flow restrictor in it but the stickers have been removed so I cant tell if the pipes are connected right. I'll get the builder to turn the rad round to see if that helps. If that makes 3/4 of it hot I may live with that rather than buy a new one.

If there is no solution for keeping the tall one, I'm planning to replace it with a Stelrad 600 H x 1000 W double panel, double convector rad rated at about 6000 BTU (delta T50) (its qiite a big room).

hot_rod

We in the US have a hard time wrapping our head around open type expansion tanks. Seems it is the leading cause of corrosion in systems also. Any way to turn it into a pressurized system?

JUGHNE

Actually the old ones we had were often in the attic covered with insulation or had a supply piped into them somehow.

Jamie Hall

There is, of course, a way -- but open expansion tanks are quite common across the pond and are very reliable. One problem with converting would be pressure -- most closed systems like ours in the US operate at twice the pressure, or more, of open systems.

mattmia2

If both connections are at the top and are above the open expansion tank the water will never be able to reach the tapping in the radiator to get any water in the radiator. If you connected the radiator at the bottom on both sides it would be able to fill to about the height of the level in the expansion tank, maybe a little more or a little less depending on exactly where the circulator is.