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The Vaillant error F28 interrupts the heating function and indicates malfunctions ranging from the gas supply to the electronics.
Vaillant error F28: Identifying causes and first steps
The Vaillant error F28 occurs when the device does not detect a flame or the ignition is blocked. In addition to gas problems, hidden defects can also be the cause. Proceed in a structured manner to save time and money.
- Check the gas supply and ignition: First, check the main valve on the gas pipe. Are other gas appliances, such as the stove, working? If not, contact your gas supplier. Press the reset button (usually red) on the appliance for 1 second – try this a maximum of three times, otherwise you risk damaging the control unit.
- Check the condensate drain: A blocked condensate pipe often triggers F28. Locate the plastic hose on the appliance (often at the bottom) and check for blockages. Rinse the pipe with warm water – no harsh cleaners!
- Clear the air intake and exhaust path: Inspect the outside air nozzle and exhaust pipe connection for debris such as leaves or ice. Use a flashlight to identify any narrowings and clean carefully with a brush.
- Check the control board: A defective circuit board can cause false signals. Disconnect the heater from the power supply, remove the cover, and look for visible damage such as swollen capacitors or corroded contacts. Note: It is best to leave repairs to professionals.
Complex sources of error and when to call in the professionals
If simple measures do not resolve the Vaillant error F28, there are often technical defects behind it. These details help to narrow down the problem – and estimate costs realistically.
- Test the ignition electrode and flame detector: The ignition electrode (metal rod on the burner) must be free of soot. Clean it with fine sandpaper – but not too aggressively, otherwise you will destroy the coating. The flame detector (ionization electrode) measures the combustion. Replace it if the resistance values exceed 15 kOhm – cost approx. $60.
- Check the gas fitting: Defective magnetic coils in the gas fitting interrupt the supply. A specialist measures the coils with a multimeter (target value: 3–5 kOhm). If it fails, you will need to replace the component – price €300–400 including installation.
- Check the wiring harness and grounding: Broken wires or loose connectors in the wiring harness lead to communication errors. Check the connections on the circuit board and on the burner. Use a multimeter to find any interruptions. Caution: Poor grounding also triggers F28 – only an electrician can help here.
- Pressure switch and lambda sensor: The pressure switch monitors the gas pressure. Tap its housing lightly – if the heater responds immediately, it is dirty. The lambda sensor (on newer models) analyzes exhaust gases. If there are faults, replacement costs from €200.
- Prioritize maintenance: Have the heater checked annually by a specialist company – cleaning the burner and condensate drainage in particular prevent F28. Cost: €80–120 per service.
- Limit DIY repairs: Never work on gas-carrying parts or electronics without expertise – danger to life! Document all steps so as not to lose warranty claims.
- Repair vs. replacement: If the cost exceeds €500 (e.g., defective circuit board + gas fitting), it is worth buying a new appliance – modern Vaillant models come with a 10-year warranty on key components.
