if the pump is situated between the cold feed and open vent pipe (pressure and temp relief, runs up to the header tank and sits over the top of it, usually arched)

it can cause air to be pulled into the system, re-arranging the pipes can sort this out, but can be a bit of a ballache lol

Its an open system i assume, header tank in the loft that feeds down to the boiler.

Prob is poor pipe set up i'd imagine.

yeah thats what I did with my bedroom one, although I snapped the bleed pin the other day and cant get it out so Im gonna have to try and rob a new rad from work

or a poor combination of pipe set up causing air entrainment rising to the bathroom rad, assuming its an open system?! should be boiler, open vent, cold feed then pump.

what kinda system is it? one way to solve it is by fitting an auto air vent higher than the point of the radiator if its possible. tbh id prob just bleed it wen it needs :lol:

it has nothing to do with the lock sheilds or being furthest away from the boiler, Its the way the heating was installed, the pipe work under the boards or the rad itself will be the highest in the system, even by only a few mm, and because air rises, it will fill the higest point which in your case is the bathroom rad. in our house its my bedroom :mad:

without major work there isnt really much you can do

At my folks house they have a standard boiler, when its on it heats the rads and the hot water tank at the sametime.

The bathroom radiator fills with air within days, its upstairs.....the furthest from the boiler i believe as it was fitted without a thermostat rad valve.

Its piping hot when i drain the air.....i'm just wondering if i need to adjust the lock shield valves on this rad in order to reduce its flow, might help ruduce the air build up?

Can you just shut off the exit pipe or will the boiler explode!?

I've had a read up online about 'Balancing a Central Heating System' but seems complicated!

Is there a set rule for setting up a rad thats furthest from the boiler?

Thanks chaps!

(i also understand the problem might lie else where, eg.....c**p build up in the system etc but wanted to try the above first)