why do my radiators need bleeding every autumn?

[misdee]

just had to bleed the one in the bathroom, trying to do the one in girls room but it wont budge, gotta check the others as well.

why? i have never had to do this in my other homes?

maybe something to do with the fact that they haven't been used all summer. Are they old?

i think its the same system from where the bungalow was built, so 15years old?