A5 alarm, electric backup heater disabled, reduced heating capacity

Safety: Turn off power at the isolator and allow the cylinder to cool before removing any covers. Risk of electric shock and scalding.

• Bleed air from cylinder circuit: If your Nibe furnace is connected to a separate hot water cylinder, bleed any air from the cylinder coil circuit and ensure the cylinder circulation pump is running.
• Check cylinder temperature: If the cylinder feels extremely hot, allow it to cool. Do not draw off very hot water; risk of scalding.
• Reset high‑limit thermostat: On many Nibe electric heaters there is a manual reset button on the safety thermostat under the cover. With power off, remove the cover, press the reset button, refit the cover, and restore power.
• Descale if necessary: Heavy limescale can cause local overheating. Descaling or replacing the immersion heater should be done by a qualified technician.

If the A5 alarm recurs, have a technician test the immersion heater, safety thermostat, and cylinder pump.