Heater displays E21 and shuts down, often during windy conditions.

Safety: Turn off power and gas if you suspect combustion instability.

• Check vent and intake orientation: Ensure the vent termination and air intake are installed per Pentair’s guidelines and are not facing prevailing winds directly.
• Inspect burner compartment: Verify burner tray is properly seated and secured. Look for gaps or missing gaskets that could allow wind to disturb the flame.
• Observe flame pattern: With a technician present, observe the flame through the sight glass. Flames should be stable and not blowing off the burners.
• Gas pressure check: Have a licensed gas technician verify inlet and manifold gas pressures match Pentair specifications.
• Wind mitigation: In very windy locations, consult Pentair installation guidelines for wind screens or venting modifications.