Boiler cuts out on hot water

Ideal Mexico 2 boiler for CH & DHW, boiler ignites and stays on when CH&DHW are on but DHW does not heat up. Boiler works fine just CH and the radiators heat up. When DHW only, boiler ignites and burns for about 2 to 3 minutes and then cuts out. Any suggestions please?

Lenny. From what you said I would suggest an air lock in either the flow or return. Turn the CH off. Turn the boiler stat right up and wait. The water will expand as it gets hot and 'should' push the air bubble out if it's in the flow. If you know what you're doing it is possible to pull the stat phial out of its pocket and let the boiler boiler very briefly. the resultant bubbles can push an air lock out. BUT, before you do any of this just get up into the loft and look in your header tank. Is there still water there? Or has the ballcock 'frozen' in the up position. The water level would drop to the point beyond the top of the flow - meaning no circulation.

easy to sort but what type of cylinder do you have

Check any air bleed point in the upper pipe going into the side of the HW cylinder. May be screwdriver, spanner or radvalve key operated. Air here would stop circ through hw circuit.