Puzzled by radiators

[mark_j_k]

OK here's what's been done already:

Radiator upstairs never got hot (you could bleed every day and still nothing), changed it and was fine.

Radiator downstairs went cold at the bottom (one pipe red hot, one cold)
Changed radiator and still nothing.

Balanced radiators to get them all hot, done.

Problem sorted? No, now one radiator (downstairs) seems to have alot of air rushing/gurgling though it constantly.

Pump is set on the middle setting '2' and the system is an open vented with a back boiler (not sure on make)

Any ideas on what I should try next?
Is it possible that air in being sucked in through a leaking radiator valve?I've been told that the radiators are from the 70's (apart from the 2 that that have been changed)

Thanks in advance.
Mark.

 

[gas4you]

Check small tank in loft has about 3-4" water in it.

Drain off some water from a drain point and check the level in the F&E tank drops and is replenished whilst draining. If not you have a blocked cold feed.

Search FAQs for this.

 

[mark_j_k]

I'll check that thanks, (it not in my house so it'll have to be tomorrow)

Would the cold feed be blocked though as every time I've drained down and refilled everything seems ok?

Cheers.