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Seisco Tankless Water Heaters

Connection to Power Supply

Canadian circuit protection disclaimer.

All wiring and circuit protection shown on this website are sized according to the US National Electric Code (NEC).

In Canada, wiring and circuit protection must be sized according to the Canadian Electric Code (CEC). The Canadian Electric Code requires that all supply wires and corresponding circuit protection for potable water heaters and hydronic space heaters be sized to a minimum 125% of the maximum current rating of the heater.

*Seisco water heater installation and service must be made by qualified personnel only!

Note: This unit must be installed to meet the current National Electric Code, and any applicable local plumbing, electrical, heating and air conditioning codes.

Install wiring from the unit to the Main Power Circuit Breaker Panel. Connect the wiring to the unit as shown on the wiring diagram attached to the inside of the unit's cover.

See Wiring Diagrams
[RA-28] [RA-22 & RA-18] [RA-14 & RA-11, RA-09]


Models RA-14 through RA-28 require multiple power sources. when wired directly to the breaker box, they require more than one double pole circuit breaker. Risk of electrical shock. Heating element is not grounded. some units have multiple power supplies. disconnect all power supplies before servicing. If using stranded wire, make sure that all strands are in secure placement in the terminal block. A loose strand in contact with the circuit board can impair performance or damage the board.

Heater Supply Side Connection

For models RA-9 through RA-11, one pair of wires should be attached within the unit at power circuit 1 [CKT 1]-one wire to L1 and one wire to L2. for models RA-14 through RA-22, a second pair of wires must also be attached at power circuit 2 [CKT 2]-one to ll and one to l2. for model RA-28, a third and fourth pair of wires are required for power circuits 3 and 4 [CKT 3 & CKT 4].

Where required by code, use a disconnect switch adjacent to the heater. when making this type of tankless water heater installation, be sure the main feeder wires used are properly sized.

Install the proper size circuit breaker (see Product Specifications). Be sure that the unit-to-power supply circuits are properly connected. For model RA-9 - RA-1l, the pair of feeders attached to power circuit 1 (CKT 1) should be attached to one 2-pole breaker, and for models RA-14 - RA-22, the second pair attached to power circuit 2 (CKT 2) should be attached to a second 2-pole breaker such that the total load will be balanced. For model RA-28, two additional breakers are required for power circuits 3 and 4 (CKT 3 & 4).

Pre-Power Check

  1. After all electrical connections have been made, every effort should be made to verify a safe Tankless Water Heater Installation. Again check to be sure all connections in the unit disconnect and/or circuit breaker panel are secure. Check to be sure that an adequate ground has been properly connected. Check to be sure that adequate size breakers have been installed properly. Remember that breakers that are too large are more dangerous than breakers that are too small.

  2. Run water through the unit until air is purged

Power Check

Check only after the Pre-Power Check has been completed and the unit filled with water. Turn on the Main Power Circuit Breakers. Verify that the heater’s GREEN POWER-ON indicator light is illuminated.

Use caution when checking voltage to the unit.

Check the voltage available to each active power circuit. SEISCO models RA-9 to RA-28 are designed to operate from a 208V to 240V power supply. Connect a voltmeter at power circuit 1 (CKT 1) between L1 and L2. (For models with multiple power circuits utilized, continue to check voltage at each additional power circuit.)

Operational Checks

Turn water on MEDIUM-LOW utilizing any sink allowing water to run for a couple of minutes to ensure that all air is purged from the unit. You will hear a "click" as the relays on the circuit board engage. It is normal to hear a "hissing" or "crackling" noise from the heat exchanger after the unit is started. With the unit's cover removed, verify with an ammeter that there is electrical current through each heating element circuit. Disregard the water temperature while doing this test

Turn off faucets after completing operational checks.

Thermostat settings are factory preset for units employing a circuit board potentiometer (thermostat).

This Tankless Water Heater Installation MUST BE DONE BY QUALIFIED AND LICENSED CONTRACTORS. Refer to your local electrical and plumbing codes for additional information

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