How to Install the EcoSmart Flow Sensor (HA-P136 / RTE10725)

The HA-P136, also sold as RTE10725 or FSA QC LS1836, is the black teardrop-style flow sensor used in compatible EcoSmart ECO 18, ECO 24, ECO 27 and ECO 36 electric tankless water heaters. The sensor reads a turbine at the cold-water inlet. When the turbine spins, the control board knows a hot tap is open.

Open or print the five-page installation guide (PDF)  ·  Shop the HA-P136 / RTE10725 flow sensor assembly

Check the sensor before ordering

Match the heater’s model label, connector and old sensor shape to the product photo. Some heaters in the same kW range use a different flow sensor. A heater that only activates at high flow can also have debris in the inlet screen or a sticking turbine.

HA-P136 / RTE10725 kit with black teardrop flow sensor, wiring connector, turbine, retaining wire and inlet screen

How to replace the flow sensor and impeller

For qualified service professionals. These heaters have multiple high-voltage feeds and can hold hot water under pressure. Follow the manual for the exact model. A qualified technician must verify all supply circuits are de-energized before touching any wiring.

  1. Shut down and drain the heater. Switch off every breaker feeding the heater. Close the cold-water inlet, allow the water to cool, and open a hot tap to relieve pressure before loosening fittings. Drain the unit as its manual directs.
  2. Remove the old sensor. Remove the cover and photograph the sensor connector and wire routing. Release the wire ties, disconnect the plug by its housing, and unscrew the sensor from the flow meter housing.
  3. Install the matching sensor. Seat it in the original position, snug the screws, and reconnect the plug to the same board socket. Secure the wire along its original route, clear of the cover and heating chambers.
  4. Clean the inlet screen and fit the new turbine. Remove the screen by its rubber edge and rinse it. Remove the retaining wire and note how the old turbine sits. For this replacement, fit the new turbine in the same orientation, then reinstall the retaining wire and inlet screen.
  5. Restore water and purge the air. Recheck the wiring, reinstall the cover, reconnect the plumbing and open the inlet. Leave all breakers off. Open several hot taps for at least 2–3 minutes and continue until the flow is steady and air-free. Check every disturbed joint for leaks.
  6. Restore power and test. Once the heater is full, air-free and leak-free, turn the breakers on. Open a hot tap and confirm the display activates with flow, the water heats, and the connections stay dry.
Pliers gripping the rubber edge of the inlet screen Flow meter turbine being removed through the cold-water inlet
The inlet screen comes out first. Note the turbine’s orientation before removing it.

If the heater still doesn’t activate

With power safely isolated, have the technician recheck the inlet screen, turbine orientation and sensor plug. E1, E2 and E3 on these ECO models point to temperature sensors. If there is a leak, scorching, damaged wiring or a cracked housing, leave the power off and contact a qualified professional.

See the illustrated 18–36 kW servicing article or check the exact replacement part and compatible models.

View the printable installation guide

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