Furnace shows 04 and shuts down, often after running for a short time

Safety: Turn off power and allow the furnace to cool fully before touching internal components.

• Check system circulation: If this Vokera furnace is part of a hydronic heating system, verify that radiators or air handlers are getting hot. If not, the circulation pump may not be running.
• Bleed air (hydronic): Bleed air from radiators or air vents according to system instructions. Low flow can cause overheating.
• Inspect filters and vents: Ensure any system filters, grilles, or vents are not blocked, restricting airflow or water flow.
• Check overheat thermostat reset: Locate the manual reset overheat thermostat on the heat exchanger (if fitted). With power OFF and unit cool, press the reset button if accessible. If it repeatedly trips, do not bypass it—this indicates a serious fault.
• Call a technician: A professional should check the heat exchanger for scale or soot, verify pump operation, and test the overheat thermostat.