hi , the guy parked next to me has a problem with his water heater. he says his batteries dropped below 11 volts and the heater cut out ,then he took the van for a spin and also gave them a good charge from his solar but since then his truma combi won't work at all. his batteries are up to 13 v now and i have checked the fuse but there still seems to be no power there at all. anyone have any ideas? cheers sean.