Boiler does not ignite; display shows A7 shortly after a call for heat or hot water

Safety first: Turn off the boiler at the main switch and isolate power at the breaker. Allow the appliance to cool before touching any internal components.

Steps to check and correct:

• 1. Power reset: Turn the boiler off for 2–3 minutes, then back on. If A7 reappears, continue with checks.
• 2. Locate the flow temperature sensor: On Buderus boilers, the flow NTC is usually clipped into the flow pipe leaving the heat exchanger (often on the right-hand side of the hydraulic block). Consult the service manual for exact location.
• 3. Inspect wiring: Check the NTC plug connection at the sensor and at the control board. Look for loose connectors, corrosion, or damaged insulation. Reseat the connector firmly.
• 4. Measure resistance: With power off and wires disconnected, measure the NTC resistance with a multimeter. Compare to Buderus NTC resistance chart (e.g., around 10 kΩ at 25°C). If reading is open circuit, shorted, or far out of spec, replace the sensor.
• 5. Check for water ingress: Inspect the sensor pocket and surrounding area for leaks that may have damaged the sensor or wiring. Repair any leaks before fitting a new sensor.
• 6. Control board check: If a known-good sensor and wiring are installed but A7 persists, the control board NTC input may be defective. This typically requires a qualified technician to diagnose and replace the Buderus boiler control unit.

When to call a professional: If you are not comfortable using a multimeter or removing the boiler front cover, or if the control board appears faulty, contact a certified Buderus technician.