Had the level sensor blow last week, replaced that and topped up system, drove to work, expansion tank behind flap was bubbling when I arrived. A mile from home on the way home heard a bang and some steam, the distribution junction had blown! So replaced the dale cap, the junction the thermostat and flushed water through all the small pipes and rest of engine making sure water flowed through them and replaced old pipes, i didn't flush through the pipes forward of the thermostat though as plain forgot that the thermostat would prevent water towards the radiator! so filled with 7 litres of coolant as per Haynes and managed to get in 5.5 litres of water, before to hot whilst bleeding in engine bay and radiator, especially the radiator as i tried to get rid of the old pink coolant that was left and screwed in the bleed screw when the new purple coolant came out. This morning I filled another 1/2 litre of water and ran the engine to high revs afor a few seconds nd then removed the cap to continue putting more water in got maybe a another 1/4 litre, replaced cap and gunned it again and as i removed the cap the tank overflowed, it wasn't even tepid.
Knackered head gasket? Also when filling tank yesterday when cold there was "smoke/steam " coming out of the tank, combustion gasses?
Had a good look on forum/wiki but nothing I could find matching this. Searched google and most situations like this do seem to be to do with head gaskets

What do you guys think?