rads not getting hot

[polar]

Hi just come back from my Mums. She has a vaillant turbomax 24 And quite a few of her rads are warm at bottom cold at top. I have tried bleeding them but nothing comes out.
The gauge on boiler is on zero, but boiler is working ok hot water and heating, I was told some time ago that boilers wont work when on zero. I was scared to top up boiler by filler loop as it is working.
Could anyone please give me the reasons and what I could do when i go back tomorrow especially if topping up don't work Thankyou

 

[Diyisfun]

You need to get the boiler to 1bar, if it drops again you have a problem..

 

[polar]

Thanks If boiler stays at 1 bar and rads still dont get hot is there anything else i can try.

 

[namsag]

Once you get the right amount of water into the system and everything bled they will get hot