SD F28e SB not hot water in water only mode?

Moved into a new house and I'm having problems with the hot water. It's a sunivar duval enviroplus f28e sb (I think). If I have it in water and heating mode the green light comes on and it fires up. I can feel hot water in the pipe and that can be felt at the water tank. Soon as I turn it to water only mode (no need for CH in summertime) the greenight goes out and it all stops. If I reset the unit with it in water mode greenlight comes on for a second then goes out and units dead.

What's going on? I'll need to call agent tomorrow as I need hot water as my 2 year old needs his baths. The honey well unit is set for hot water continuous with CH off. It's hot enough as it is without running g the CH just to have hot water.