boiler turns off due to overheating

[MilesJ]

Yesterday flushed central heating system out and then refilled and since then the hot water works but when turning in the central heating the boiler then turns itself off due to overheat what do I do now any ideas as heating working fine the day before just one not so but the stuff in the header tank to get rid of any sludge etc thats why I drained system down and now this what do I do next?
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[dcawkwell]

Diverter valve or zone valve not opening?
No circulation going on.