Thermo Products Models from 8 kW to 24 kW : 240 Volts ( single phase ) Boiler Wiring

cold water supply line between the COMBOMAXMC unit and flow check valve. Contact your installing contractor, water supplier, local plumbing inspector or plumbing supply house for assistance.

3.6.3Recirculation line (if applicable)

If a recirculation line is installed, the return connection should be made to a tee close to the inlet connection on the water heater. A check valve should always be installed in the recirculation line to prevent cold water from entering.

3.6.4Domestic hot water temperature and pressure relief valve

An automatic temperature and pressure relief valve must be installed at set-up time. No valve of any type should be placed between the safety relief valve and the water heater. Use a tee to set the relief valve onto the hot water outlet. The pressure rating of the relief valve must not exceed 150 psi.

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 recorded on the boiler(s) rating plate. For a circulating tank installation, the separate storage tank(s) must have similar protection.

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.

3.6.5Thermostatically controlled mixing valve (included)

For general-purpose hot water requirements in a domestic environment, a thermostatically controlled mixing valve is recommended to reduce the risk of scald injury. Contact a licensed plumber or the local plumbing authority for further information. Adjust the mixing valve to the lowest required temperature setting.

3.7 BOILER WIRING

The boiler cabling and grounding must conform to local codes or, in their absence, to the National Electrical Code.

Power must be provided by a 120/240 volt (single phase, 60 Hz) circuit, appropriately fused and with 3-wire plus ground cabling of sufficient gage. The fuse and cabling gauge may be determined from the boiler rating plate.

3.8 CIRCULATOR WIRING

The COMBOMAXMC heating pump (120 Vac, 1/25 Hp) is connected to the C&C terminals on the boiler electrical panel. The control circuit is designed to start the pump upon receiving a heating signal from the thermostat or priority aquastat.

3.9CONNECTING THE THERMOSTAT 3.9.1 240V models

3.9.1.1 Single heating zone

Connect the low-voltage thermostat to the T&T terminals on the COMBOMAXMC electrical panel (DO NOT apply current to these terminals). (see figure 10).

3.9.1.2 Zone valve zoning

Connect the low-voltage thermostat to the zone valve. The components must wired such that, upon a heating signal from a thermostat, only the corresponding zone valve will be actuated and will in turn activate the COMBOMAXMC circulator relay. Connect the zone valve switch to the T&T terminals on the COMBOMAXMC electrical panel (DO NOT apply current to these terminals). See figures 9 and 10.

The transformer used to power the zone valves must be of sufficient capacity to handle the load represented by all zone valves.

3.9.1.3 Multiple circulator zoning

Connect the low-voltage thermostat to the relay (Honeywell #RA-889, RA-89A). The components must wired such that, upon a heating signal from a thermostat, only the corresponding circulator will be activated. See figure 9.

3.10 PRIORITIZING TERMINAL POST

The K&K terminals on the electrical panel create a dry contact when the domestic hot water priority aquastat contact closes.

COMBOMAXMC Electric boiler Set-up, use and care guide (revised January 2006), Page 8.