Try bleeding all radiators starting downstairs, you could of got some air in the system which when pushed into the boiler is causing it to overheat and go off and this is why when it cools down you can start again.
Been to one today with the exact same problem except auto airvent had been leaking and crusted itself up.
Quoted for new one (less than £55.00 inc Vat and labour) and customer said they will struggle on, its now cost them an hours labour for the ten minutes i was there which i would have knocked off if they had let me do the job for them.
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