pls help. my mums boiler baxi solo is overheating . was airlocked fewe months ago and was cleared. cant afford to pay for plumber before xmas. how can i remove airlock?its a 2 story house with 8 rads. isolate tank in loft, hose to drain point vent rads then close rads and hope refill pushes out air? have i got that right?? thankyou