i  no im to late to anser this but sounds like air taped in heating pipe 
1 unscrew bleeding valve should be near thermostat 
2 unscrew colant bottle where water goes in 
3 GET 3 3 empty bottles of cock ext cut bottoms of and place all 3 together .
4 put bottles in the water collent bottle .
5 get a hose pipe and pure in the bottles for aprox 20 to 30 mins to flush air flow out
                
 sam
                
 January 2010