Your main problem is the Aqua-Hot Diesel Switch. When you turn that switch ON an indicator light should light up and STAY lit. If that light does NOT light up at all, then either the lamp inside the light has blown or you have some other problem going on inside your Aqua-Hot unit.
If the light comes on and then goes off that also points to a possible problem in your Aqua-Hot unit.
There should be a control board inside your Aqua-Hot unit with a bunch of lights on it hat need to be checked.
Here is the link to your Service Manual
which has some great information about the operation of the switches and various trouble-shooting steps.
The reason you have hot water is most likely due to the electric assist working BUT to have enough heat for the baseboard heat exchangers the diesel needs to run.
It appears that your diesel burner is not igniting.
Also, I would strongly suggest that you join Roger Berke's Hydroninc Heating Forum.
Dr4Film ----- Richard