radiators need bleeding weekly-any idea why?

My old Mum lives in a small bungalow, containing 3 radiators only, and a 20 year old baxi boiler. This winter I have noticed that the radiators often need bleeding, with a cosiderable amount of air coming out. It's usually the one in the bedroom that is worse.

Any idea where the air is getting into the system?

On a side issue, last weekend she complained that only the bathroom radiator was getting hot and the boiler was noisy. When I had a listen, it sounded like the flow through the pump was water then air, water then air. I had a look in the loft at the header tank and found it to be empty of water. I forced the ball valve down to half fill the tank and the system quietened down and the other rads got hot.

It seems like it hadn't been topped up after the bleeding I had been doing. She told me that a plumber went up there a few years ago to address an overflow fault. It looks like all he did was bend the ball arm down tho the bottom. I can sort this issue myself, but just thought I would mention it.

Hi

The system probably needs cleaning. And a dose of inhibitor to stop it rusting away too quickly.
Has the BB been serviced regular?

Up until a few months ago she had been paying one of these schemes where it gets serviced and call out cover. We cancelled when we thought they were just going through the motions and not actually doing a great deal. On one of their services, they wouldn't even bleed the rads.

I liken those services contracts to a person taking their car for a service and all is replaced but the oil.