Hello I have a vented system, ideal Logic Heat 15 (2 years 4 months old), grundfos Alpha 2L pump also 2 years old. All was well in the evening, morning came no heating or hot water, fault code on boiler f-d (indicates flow problem) I have also noticed the pump which is one of the new intelligent pumps appears not to function and sits in power on mode. I have checked the header tank, dirty but water is flowing through, (i have cleaned this out completely now) water definitely getting through as the filter unit releases flow quiet fast when opened, checked drain valve downstairs under bottom radiator and water pretty clean, checked the water on return at boiler and seems clean. Will the boiler not firing render the pump to idle or would a fault on the pump stop the flow to the boiler ?. I am unsure on a Sunday where else to check. I have not yet refilled the header tank in case i need to remove something else and check. When header empty the filter does not release any water so indicates not blocked to me ?. Awaiting a call from an engineer but unsure when this will happen.( I am thinking it could be either the pump which would surprise me) or a faulty thermistor in the boiler. Any suggestion very welcome