Honeywell SDC Service Manual page 197

SDC / DHC Hydraulic Components
The electrical heating element will be enabled if the temperature
value has dropped below the electrical water heater offset (EWB-
Offset) of the hot water setpoint (Parameter 29, "Hot Water"
Menu) and the switch-on delay (Parameter 28, "Hot Water" Menu)
has elapsed afterwards.
This function allows setting the hotwater setpoint WS to a
temperature value that has dropped below the EWB-Offset of the
hot water setpoint. As soon as the hot water setpoint is reached,
the function will be disabled again. The heat generator demand is
switched off while EWB is active.
This application is useful for switching on the ELH in addition in
case an electrical water heater has turned out or the capacity of
the heat generator for the hot-water loading is not sufficient.
Start: WW - demand
WS
EWB - Offset
EWB – Deactivation
EWB – Switch-on delay
EN2H-0221GE51 R0812 197