One radiator cold at top but slightly warm at bottom - help!

[Mr Gillespie]

All radiators in house work perfect apart from the one in main bedroom (closest to water tank if this is important?).

Once it is bled it heats up from top to bottom perfect.

After a few days it then goes back to only getting slightly warm at the bottom but cold at top.

Any ideas?

PS I have recently been given some liquid which I was told to pour into the water tank in the loft to get the flow of water better within the system - this has not worked.

 

[gas4you]

If you're having to keep bleeding it, then air must be getting sucked in from somewhere.

Open vent would be prime suspect. Go in loft with jam jar of water, place over open vent, get someone to turn on heating and see if water is sucked out of jam jar.

 

[Mr Gillespie]

When you say place over open vent - how do you mean? I am not the brightest when it comes to plumbing issues.

 

[gas4you]

Place the open vent into the jam jar full of water.

 

[Mr Gillespie]

Where would I find the open vent? Next to the tank in the loft?