A boiler-engineer will be able to help you - and you do not mention the make or model or style of your boiler.
Notwithstanding a frost stat the timer programmer is the primary control device - the tank stat controls hot water firing and the room stat controls central heating firing.
You do not mention the condition of these controls when the boiler fires up erroneously. Neither do you say if the controls work correctly at any time.
Peccavi
May 2010
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