Boiler-Valliant Ecotec Plus-won't power up, display off?

My boiler has switched itself off and won't power up again. There is nothing on the display (or lights on the box between the mains swith and the boiler).
The pressure was low so I've topped this up, checked the fuse on the main household fusebox, switched it off and on etc.
Could it be a fuse somewhere? How would I access this?
Thanks