Boiler control displays E5 and unit will not start

Safety first: Turn off power. Be cautious when adding water to a hot system; thermal shock can damage the boiler.

• Check pressure gauge: Read the boiler's pressure gauge. For most Utica hot water boilers, cold pressure should be around 12 psi and not below the low-pressure cutoff threshold.
• Open fill valve: Ensure the automatic fill valve (pressure reducing valve) is open and the manual shutoff to the water supply is open. If the gauge does not rise when the fill valve lever is lifted, the valve may be clogged or the house water supply off.
• Manually add water (if safe): If you are familiar with your system, you can slowly add water through the fill valve while monitoring the gauge, stopping at the recommended pressure. Do not exceed 25 psi on typical residential systems.
• Inspect for leaks: Walk the piping, radiators, and baseboards looking for visible leaks, wet spots, or dripping relief valves. Repair leaks before refilling repeatedly.
• Check pressure sensor: On modulating condensing Utica boilers, locate the electronic pressure sensor on the hydronic manifold. Inspect wiring and connector. If the gauge shows normal pressure but E5 persists, the sensor may be faulty and require replacement.
• Reset and test: After restoring proper pressure, reset the boiler and verify normal operation.