Boiler shows E5 and will not fire; may occur on cold start

Safety first: Turn off power. Do not add water to a very hot boiler; allow it to cool to avoid thermal shock.

Steps:

• Check system pressure: Read the boiler pressure gauge. If below the recommended cold-fill pressure (often ~12 psi), slowly open the automatic fill valve or manual feed valve to bring pressure up.
• Inspect for leaks: Walk the system and look for water around radiators, baseboards, near the Peerless boiler, and at relief valve discharge piping.
• Check low water cutoff (LWCO): Many Peerless boilers use a probe-type LWCO. Shut power, remove the probe, and clean any scale with a wire brush. Reinstall with proper sealant.
• Verify pressure sensor wiring: On modulating condensing Peerless models, ensure the pressure transducer wiring harness is secure.
• If pressure will not hold: A technician should locate and repair leaks, test the expansion tank, and replace the LWCO or pressure sensor if defective.