Cold radiator

[JMM]

I have recently drained my central heating system to add a new radiator in the kitchen. The radiator is a single (600x700mm).

When I refilled and bleed the system, one of the radiators has stayed cold whilst the other get hot. This radiator has been bleed but all that comes out is cold water. The pipe to the radiator valve is warm.

Any help would be much appreciated.

Cheers... John

 

[MANDATE]

If you have bled the radiator and there is no air pocket,then I would be ensuring that both valves are open.
Alternatively close the valves,remove the radiator and flush out, sediment could cause a blockage

 

[MANDATE]

John,
Just thouht, I can recall a similar problem caused by an air lock but not in the radiators.
It was where pipework up, along and then down againand air got trapped when the system was being filled.
As I recall I increased the boiler temperture, increased the pump speed to cure it.

 

[JMM]

I have just flushed the radiator out with a hose pipe. This cleared out a lot of black gunge, I ran the pipe til the water ran clear.

I have replaced the radiator, bled the air out, it got warm for a few minutes at the top, and went cold again.

I have increased the boiler temp, but I don't think i can increased the pump speed.

How long should I keep the boiler temp up for

 

[JMM]

Having read some of the other forums on cold radiators, I had better add that the radiator in question has a balance valve on one side and a small square type nut on the other.

The radiator is now stone cold whilst all the other radiators are very hot

Any more help will be much appreciated

John [/img]

 

[MANDATE]

I would only increase the boiler temperture for five or ten minutes till the problem is cured.
Pumps usually have 3 speeds, adjustable with a lever (or maybe a switch in your case)
Something else I've done that may help.
Got two 'tap connectors',mine are actually on a'bend' fasten them to. about 6ft fo clear plastic tubing with jubilee clips ( I used those plastic securing straps about 3mm wide with ratchet action)
Then remove radiator and replace with plastic tubing assembley using fibre washers to ensure no leakage
When you open the valves you can see if water is flowing and in which direction with the system on
And with the system off disconnect each end in turn and run off a bucketful or two of water, this should move any airlocks elsewhere in the system, it will also tell you if your valves are opening OK.

The problem has got be caused by either blockage or an airlock.

One thing I omitted to mention earlier also to turn up the room stat to keep the pump working longer and as air collects in your radiator bleed it of at regular intervals

 

[MANDATE]

Regarding the valves, both these are probabley lockshield valves.
One is provided with a handle and used for on/off only.
The other is adjustable to control the flow and is probabley only open a little, remove the handle from the on/off valve and use it open up the other valve(maybe sediment at this point) or you can use small spanner
I should try this option before the others
Let me know how you go on

 

[JMM]

Thanks for the advice.

I've drained the radiator and ran both taps into buckets until they both ran hot water.

Put the radiator back on, and touch wood, it has stayed hot.

I will wait and see what happens in the morning when the heating has been off overnight.

Just a quick point, how many radiators can a standard central heating pump cope with (Myson Multi Head II). At present, I now have 7. The reason I ask is, the radiators get hot, but you can keep your hand on them for quite a while.

Thanks again.

John

 

[MANDATE]

John,
I don't know the limit for the number of radiators,but I have 9 radiators 3 being at least 8ft long, 1 is not on the pumped circuit(bathroom)
and they get quite hot.
I know that grunfoss do pumps that cope with a head of water of 5 metres and another at 6 metres at about £5 difference in price so that itself shows that pumps can vary in pressure output.
You could set the boiler stat a little higher, although in theory the water temperture is the same at all radiators in practice the water is losing it's heat as it travels along, the amount it loses is dependent on the air temperture surrounding the pipe work and how good the insulation is.
For about £7 you can purchase a clip on pipe thermometer and observe the temperture going into the radiators on different boiler settings as against the temperture as it leaves the boiler
Anyhow it appears prolem solved ,it will be OK in the morning

 

[JMM]

Radiator is still hot this morning.

Thanks for your advice.

Cheers... John