Ruud tankless water heater does not start when a small hot water tap is opened; no error code displayed.

Safety first: Ensure the unit is properly installed and vented before extended operation.

• Step 1 – Increase flow: Open the hot water tap further or use a larger fixture to see if the heater starts.
• Step 2 – Clean aerators and showerheads: Remove and clean debris or scale that may be restricting flow.
• Step 3 – Clean inlet filter: Turn OFF water and clean the inlet filter screen on the Ruud tankless unit.
• Step 4 – Replace flow sensor: If the unit still fails to detect flow at normal usage levels, replace the OEM Ruud flow sensor as described in the E5 procedure.