I use a thermostat in the separate heating loop, which is connected to the webasto loop by a heat exchanger (see drawing at previous page).
So the webasto is free running just with it's internal thermostat. But AFAIK it has a control input which can be used to turn it on and off by a thermostat.
This setup has the advantage that the warm water heater always gets the full heat of the webasto, even when there is no heat for space heating required.
Hmm. Do those have a wait time for hot water? Seems like diesel can't fire up fast enough to provide instant hot water.
Just glanced at their site. Seems like it's no different that hot water systems that many have built using an espar and heat exchanger to heat water.
Does anyone know a vendor that makes a diesel tankless hot water heater. It should be similar to a propane or natural gas TANK-LESS water heater, except diesel generates the heat. I want it to be a "stand-alone" on demand heater that is NOT integrated with the main engine cooling system and not connected to any heat exchanger.