Boiler shows E5 and shuts down, often accompanied by gurgling sounds

Safety first: Let the boiler cool before opening any valves. Use caution when working around the relief valve.

• Check pressure gauge: Confirm the system pressure on the boiler gauge. If it is below the recommended range (often 12–15 psi cold), the boiler may lock out.
• Refill system: Open the manual feed valve or verify the automatic fill valve is functioning. Slowly bring pressure up while monitoring for leaks at radiators, valves, and the boiler.
• Inspect expansion tank: Tap the expansion tank (often mounted above the boiler or on the return piping). It should sound hollow on top and solid at the bottom. If it is full of water, it may be waterlogged and needs replacement.
• Check relief valve: If the pressure relief valve is dripping, it may be stuck or opening due to overpressure from a failed expansion tank. Do not cap or plug the relief valve.
• If pressure is normal but E5 remains: The pressure sensor or switch on the Pennco control board may be defective. Replacement should be done by a technician.