Thermo Products COMBOMAX Models from 8 kW to 24 kW : 240 Volts ( single phase ) - Manual (Page 9)

COMBOMAX MC Electric boiler Set-up, use and care guide (revised January 2006) , Page 9.
3.11 BI-ENERGY SETUP
To take advantage of a special domestic electric
utility rate, your COMBOMAX
MC
boiler can be
combined with an existing oil or gas-fired
furnace. Please contact your utility to make sure
your building is eligible and to find out about the
new wiring configuration. Please refer to figures
7 and 8 for the set-up required.
The CBE-EM bi-energy switching control
(available as an option) is especially designed to
satisfy utility requirements. The CBE-EM control
selects the cheapest energy source according to
the outdoor temperature, the indoor temperature
setting and any signal provided by the utility.
The CBE-EM bi-energy control starts up the oil
burner upon receiving the appropriate signal,
even if the thermostat is sending no heating
signal. The oil burner stops when the boiler
reaches its high-limit point. For this reason, the
plumbing system must be equipped with a flow
check valve or zone valves.
The 3-way zone valve (1’’ NPT F) which comes
with the CBE-EM control, directs the heating
water to the oil burner or the COMBOMAX
MC
unit depending on the signal sent to it by the
external bi-energy sensor. Thus, your oil burner
can cool down while eliminating energy losses
up the chimney or by conduction in the furnace
room .