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The Seisco control depends on the temperature information it receives from each of its temperature sensors to detect water flow and maintain proper temperature.  If any sensor or its connection to the control board is bad, the unit may not turn on at all or if it does, the temperature may fluctuate.  Whenever servicing a unit, the proper operation of the sensors and the control board should always be verified regardless of the trouble code as these two items are critical to the continued reliable operation of the unit and often can lead to misleading trouble codes including false high temperature and element codes.  Seisco recommends you follow the pre-service checklist every time you service the unit to verify proper operation and avoid callbacks.



Verify Installation:

  • Verify proper plumbing, cold to the inlet, hot to the outlet (Cold is on the right on Signature Models).

  • Verify flow rate matches the specifications of the unit (especially at times when incoming water is colder than normal).

  • Verify the heater is mounted correctly on the wall with the fittings of the heater on the top. (Fittings must point up on Signature models).

  • Make a note of serial number in case you need to contact SEISCO Customer Service.


Tests with Power OFF:

  • Verify water flow through the heater. Check that shut off valves are in the open position and that all air has been purged from the heating chamber(s).

  • Check the plumbing and the heating chamber for any signs of leaks.

  • Check for any loose wires to the control board and verify the power connections are tight. If stranded wire is used, check that all strands are inside the lug. Check high limit switch and reset as necessary (4CH Signature Models only).


Tests with Power ON:

  • Verify circuit breaker(s) are turned on and labeled correctly (Signature models can have 2 to 4 breakers).

  • Verify power to all circuits connected to the heater. Check the voltage across the lugs labeled L1 & L2 for each circuit.

  • Finally, check the control board LED for any diagnostic codes. (Note: the control board will blink red and beep when breakers are turned on, then remain blinking green during normal operation)





























READING DIAGNOSTIC CODES: The LED status lamp located on the control board will flash a three-part sequence (two part for Flagship Models 1CH) of red flashes, each representing the individual digits of the code. After each sequence, the LED will flash green and then repeat the diagnostic code. THERE MAY BE MULTIPLE CODES SO VERIFY ALL SEQUENCES. Press the small blue mode button on the control board for two seconds, and the speaker will audibly beep the code as it flashes.
















































SENSOR MATCHING PROCEDURE (2 and 4 Chamber Models Only)

  • Turn off power and run hot water for 5 minutes or until cold. With water running:

  • Unplug the brown wire at the limit switch above the left hand corner of the control board.

  • Restore power to the unit it will beep four times, and then pause. You will then get one audible beep, a pause, two beeps, a pause, and two beeps.

  • Press and hold the blue reset button for approximately 8-10 seconds, then release. You should hear a short, low tone buzz.

  • Turn off power; Turn off the water; Reconnect the brown wire to the limit switch.

  • Restore power to the unit. You will hear 4 beeps then listen for the unit to “click” (takes up to 45 seconds) then turn on the hot water at a sink and test for temperature and normal operation.

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