Vaillant turbomax vuw hws problem ignition indicator flashes?

When calling for hot water the boiler does not kick in and ignition indicator flashes but it can be resolved by turning boiler off a few seconds and back on again. The hot water semms to be fine after that but once it has been run a few times the ignition indicator starts to flash again and it does not produce hot water. ANY IDEAS ANYBODY?????????????
Jenny Paling, January 2006


done
Air pressure switch

Vaillant engineer, January 2006
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