Safety first: Turn off power and isolate both heating and domestic water supplies. Allow the boiler to cool.

Step 1 – Observe operation: When switching from space heating to DHW, listen for the diverter valve motor. If silent or clicking repeatedly, the valve may be stuck.
Step 2 – Inspect actuator: Remove the diverter valve motor/actuator from the valve body (usually held by screws or clips). Check for water ingress or corrosion. If the motor is seized or water-damaged, replace it.
Step 3 – Check valve movement: With the actuator removed, gently turn the valve spindle with pliers. It should move smoothly. If stiff or stuck, the valve body is scaled or obstructed and should be replaced or cleaned by a technician.
Step 4 – Verify feedback switch: Some Rheem diverter valves use microswitches or position sensors. Test continuity as the valve moves. Replace faulty switches or actuators.
Step 5 – Reassemble and test: Refit the actuator, restore water and power, then test both heating and DHW modes to ensure proper switching.

Warning: Do not force the valve spindle excessively; this can crack the valve body and cause leaks.

Boiler displays E16 and may shut down when switching between heating and DHW

Possible Causes