Thermo Products COMBOMAX Models from 8 kW to 24 kW : 240 Volts ( single phase ) - Manual (Page 6)

COMBOMAX MC Electric boiler Set-up, use and care guide (revised January 2006) , Page 6.
Install shutoff (ball) valves for servicing
convenience. Install thermometers on the inlet
and outlet lines.
Never plug the pressure relief valve to avoid
creating a hazardous situation.
3.5.2 Flow-check valve
If the heating system uses a single circulator, a
flow-check valve must be installed to
minimize gravity flow and heat loss during non-
draw periods.
3.5.3 Pressure relief valve
No boiler set-up is complete without a pressure
relief valve. Its pressure rating must not exceed
30 psi (207 kPa). It must conform to the « ASME
Boiler and Pressure Vessel Code» and limit the
boiler operating pressure. It is a safety device,
not a control device.
The BTU per hour rating of the relief valve must
equal or exceed the BTU per hour input of the
boiler(s) or heat source(s) as marked on the
boiler(s) rating plate.
Connect the outlet of the relief valve to a
suitable open drain, with the discharge at most
6” above the floor, far from any live electrical
parts. The discharge line must pitch downward
from the valve to allow complete draining and be
no smaller than the outlet of the valve. The end
of the discharge line should not be threaded or
concealed and should be protected from
freezing. No valve of any type, restriction or
reducer coupling should be installed in the
discharge line. Local codes shall govern the
installation of relief valves.
3.5.4 Operating pressure control :
expansion tank
Operating pressure control components ensure
minimum and maximum operating limits are
observed within the design operating
temperature range. These components allow
bleeding air from the piping, prevent boiling and
cavitation at the circulator inlet, while minimizing
the amount of fresh water input. Please contact
a qualified plumber or contractor for more
information on this subject.
The expansion tank connection point must be
carefully chosen to prevent a situation where
closing a valve would isolate the tank from the
boiler or any part of the circuit. It is preferable to
use a calibrated diaphragm expansion tank.
3.5.5 Makeup valve
Connecting a makeup valve must be done
according to code. This valve must include a
flow-check valve to maintain the minimum
operating pressure by admitting fresh water from
the cold water supply line in case a leak occurs.
3.5.6 Air bleeder
There should be as little oxygen as possible in
the heating circuit to prevent corrosion. As
foreseen in section 3.5.4, this excludes the use
of air as a pressure regulator within the circuit.
Installing manual or automatic air bleeders
prevents air accumulation within the system.
The bleeders must be set at the highest points
of the system to purge any air accumulated
during system set-up and to check its air
tightness. Bleed the air regularly from the piping,
making sure the heating water causes no bodily
harm or material damage.
3.5.7 Circulator zoning
A flow-check valve must be installed in each
zone, preferably at the outlet of each circulator,
to prevent water flowing to zones where no heat
is currently required. (see figure 4).
3.5.8 Zone valve zoning
Zone valves with low pressure drop are
recommended. (see figure 3)
3.5.9 Circulator selection criteria
The COMBOMAX MC boiler includes a pre-
mounted circulator. The information below will
help you select additional units for multiple
circulator set-ups.
3.5.9.1 Pump flow rate calculation
The boiler output rating must correspond to the
calculated heating load. Use the equation below
to calculate the pump flow rate: