Consumption electric power of WA500 (A)-Condensation latent heat (*)(B)＝heating value(C)

(A):  Heater capacity×860Kcal = 3.8(Kcal)×860 = 3500Kcal/H
(B):  Pumped volume of water×water density×latent heat of water = 5×1×540 = 2700Kcal/H * Underlined values are quantitative.
(C):  3500 - 2700 = 800Kcal/H
Therefore, the heating value is 800Kcal/H

Heating value is almost zero when the tank is full and the heater is OFF.  No heat is generated at the heat controller.

*Condensation latent heat:  Heat is conducted to the coolant to discharge the heat outside.