No hot water on my worcester/Bosch combi 24i?

Boiler has been working fine for the few years we have been in this house. Every thing was fine until last weekend when the water pressure into the house dropped right off, hardly a trickle. I suspect the was either works or major leak on the road mains somewhere. Pressure was back to normal the next day. Now we seem to have a problem with the DHW not firing up the boiler. We can get hot water if the heating is on, obviously this is because the heating fired up is heating up the water to. Any suggestions on the possible cause would be appreciated.