[MichaelNRW]

"the blow by heater does a better job and also heats the small cooling circuit."
4NE does not heat the engine, and cooling circuit !

I may used the wrong SA in my description, the correct one is 536.

Please have a look at a G20 and "Stationary auxiliary heater".

Stationary heater circulating pump

The stationary heater circulating pump maintains the coolant circuit during auxiliary heating operation and in the necessary after-run.In auxiliary heating mode, the coolant pump assists the circulating pump.
The stationary auxiliary heater control unit activates the circulating pump directly.

Coolant changeover valve, stationary auxiliary heater

The stationary auxiliary heater coolant changeover valve controls the flow of coolant to the auxiliary heater.
The stationary auxiliary heater coolant changeover valve is a 3/2-way valve. The valve controls the supply to the stationary auxiliary heater as follows:

• From the radiator feed
  
• or from the reverse flow from the heating system heat exchanger
  

The stationary auxiliary heater control unit (control unit of the auxiliary heater) activates the coolant changeover valve of the stationary auxiliary heater directly. The switch-on and switch-off message comes from the engine control unit (DME or DDE) as well as from the IHKA control unit