Upon restarting the central heating for the winter period the following 2 things have occurred (I don't think they're related)
1) One of the rads only gets hot at the bottom (3/4 inches up the rad) the rad does not want to bleed i.e. no air coming out.
2) AND MORE WORRYING ! - once or twice during the central heating period a huge amount of water spews out out of the overflow pipe from the header tank (only for about 20/30 seconds) then it's o.k. again. I have read previous answers on a similar theme i.e. a leak between the 2 systems but might have thought this would produce a small trickle rather than a large gush !

Any help would be much appreciated.

Pressure in the system is to high, should be 12 psi cold and about 18 hot, pressure relief valve lets go at 30 psi. Expansion tank could also be bad. Note, I see a lot of people going to Lowe's etc... and buying expansion tanks to do it them selves, these won't work since they are for domestic water and are pressurized too much.