Safety first: Turn off power and close water isolation valves before removing any flow components.

Step 1 – Identify which flow sensor: On combi Rheem boilers, there may be a DHW flow sensor and a system flow sensor. Determine which circuit is affected (DHW or heating).
Step 2 – Check for flow: Open a hot water tap fully (for DHW) or ensure heating zones are open. If there is good water flow but the boiler does not recognize it, suspect the flow sensor.
Step 3 – Remove and inspect sensor: Carefully remove the flow sensor or switch from its housing. Look for scale, debris, or damaged turbine/float. Clean gently and ensure free movement.
Step 4 – Electrical test: For reed-switch types, test continuity while manually actuating the float or turbine. For Hall-effect sensors, a technician can test output voltage while water flows. Replace the sensor if it does not respond correctly.
Step 5 – Reinstall and test: Reassemble with new O-rings if needed, restore water and power, and test operation.

Warning: Leaks at flow sensors can cause electrical damage. Always check for leaks after reassembly.

Boiler shows E17 and may not fire even though there is a call for heat

Possible Causes