No heat at the top of the hose (2nd floor)

[opps]

Hi all.

Mum's (3 story) house has two rads on the top floor. The single rad has not been hot for ages. The towel warmer regularly needs bleeding. Rads on the ground and first floor seem to be OK.

Yesterday she tried to bleed the single rad. She heard a little amount of air escape and two inches of the lower part of the rad started to become warm. She then decided to bleed the towel warmer, but there was no air escaping.

Now both are cold.

I removed the bleed nut on the towel warmer (whilst the bleed valve on the single rad was open) and tried to blow into it. After blowing, I could hear a very slight gurgle but I have no reason to believe that the level of water in the towel warmer changed.

The header tank is about 4ft higher than the top of the towel warmer. I checked the header tank, it is full and the ball float valve works fine.

I looked in the cupboard where the immersion heater is (first floor).



The left hand side of the air separator is hot, as is the pipe coming out of the top. The pipe to the right runs down to the Grundfos pump and then (I assume) acts as the return from the two rads on the floor above. Next to the air separator, it is warm, but as you go up the pipe, it becomes colder.



The next image is from below the Grundfos.



Any suggestions with regards to sorting this out? My experience of radiators is limited to combi systems.

If it helps, I believe that the cold water in the ensuite bathroom is mains pressure if I need to remove a rad and use that water to try to blow away any obstruction from the return side.

Thanks in advance?

 

[Stuckinarut]

Check the feed and expansion cistern is filling back up. (Think of it as a filling loop).

 

[opps]

Check the feed and expansion cistern is filling back up. (Think of it as a filling loop).

Thanks, I did check the header tank. I was full.

 

[opps]

Very odd....

With the heating turned off, this morning both rads filled up nicely when bled. With the heating turned on after bleeding, they both got hot...

On gravity systems, should bleeding only ever been done when the heating is turned off?

Something else which surprised me was that the taller of the two rads was bled first. When the second one was bled, the taller one didn't require any re-bleeding, is that normal? Sorry, I am only used to pressurised heating systems. I guess that the header tank automatically replaces the space previously occupied by air.

The next time air enters either of the rads, I will use a lighter to see if the "air" is flammable. If it is which product should I pour into the towel warmer.

Once again, many thanks.