Tall radiator too high so cant bleed all air out

[dwilden]

Hi,

I've just replaced an ancient 500mm high radiator in an upstairs bedroom with a new 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 thing 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 across the top and one across 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 only 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?

Any help gratefully received before I bite the bullet and buy a less tall replacement radiator.

Regards

Dave

 

[oldbutnotdead]

Oops.
1 It might work but its a very bad idea (air + water =corrosion)
2 Yes many vertical rads must be plumbed the correct way round.
3 Ye canna change the laws of physics. Yes you could fill the rad while its at a jaunty angle but (since your system is not sealed) soon as you stand it up the water will migrate back to the f & e tank (with lots of gurgling)
Get a different rad.

 

[Mottie]

Can you raise the header tank?

 

[dwilden]

@aolbutnotdead - I agree with your points 1 and 2, but not sure about 3. If the rad were to empty again, that would leave a vacuum in the top of the rad, wouldn't it?

Dave

 

[HERTS P&D]

Get a smaller rad.

Andy

 

[oldbutnotdead]

@aolbutnotdead - I agree with your points 1 and 2, but not sure about 3. If the rad were to empty again, that would leave a vacuum in the top of the rad, wouldn't it?

Dave

Thats why you would get the gurgling from any air in the system eventually finding its way into that rad. You are partly correct though, it wouldn't drop back to level instantly (assuming pipework is down and up from that rad).

 

[Madrab]

If the rad has a baffle then it's designed to port the flow to the top of the rad, work across and then gravity circulate down the verticals, if theree isn't water at the top, it just wont heat properly.

As suggested, time to bit the bullet and put in a smaller rad and if you need it to heat the room, change it to a convecting rad. These designer column rads are really quite shoite at space heating anyways in anything but the smallest of rooms. Basically they're as effective as glorified towel rads.

 

[Johntheo5]

These column rads really need every thing going for them but before consigning it to the bin maye worth removing the rad valves and see if you can push a thin rod right through from one end to the other or shine a light at one end and sight it from the other end, if you have plugs at the top end do the same. You could then screw in one of these at the rad inlet side and it may just give you some circulation, worth a go?. I have a conventional type 22 rad in a converted attic to bedroom and it allways runs with a slight vacuum even though the F&E tank water level is < 150 mm above the top of the rad and the circ pump 5M below pumping into the boiler return, it heats up perfectly well.

 

[kidgreen61]

You could always fill it by pouring water in from the vent plug at the top.
As to whether it will work properly....?

 

[Johntheo5]

You could always fill it by pouring water in from the vent plug at the top.
As to whether it will work properly....?

Its like a U tube, if you try that it will only raise the level in the F&E tank to the same level, all you can do practically is (without raising the F&E tank)
to bend the ball cock to raise the F&E tank fill level so that its just below the overflow level when the whole system heats up.

 

[Tetrarch]

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?

This sounds like fun. Is there enough play in the pipework for you to lay the rad down flat, fill, bleed and then refix?

Regards

Tet