Boiler locks out with error 14; unit may overheat and shut down shortly after firing.

Safety first: Turn off power and gas. The boiler and pipework may be extremely hot; allow full cooling before touching any components.

• Check system water flow: Ensure all isolation valves on the boiler flow and return are fully open. Verify that radiators or heating circuits are not manually shut off.
• Bleed air from system: Airlocks can cause localized overheating. Bleed air from radiators and any automatic air vents near the boiler.
• Inspect circulation pump operation: With power restored briefly, listen and feel for the pump running when there is a heat demand. If the pump is silent or excessively noisy, it may be seized or failing and should be replaced by a technician.
• Descale heat exchanger (professional recommended): Heavy scale in Rinnai condensing heat exchangers requires chemical flushing with appropriate descaling agents and pumps. This should be done by a qualified technician to avoid damage.
• Do not bypass safety devices: Never attempt to bypass thermal fuses or overheat thermostats. If error 14 persists, have the thermistors and overheat cutoff checked and replaced as needed.