⚠️ IMPORTANT SAFETY WARNING: Working with gas appliances can be extremely dangerous and should ONLY be undertaken by a qualified, Gas Safe registered engineer. The information below is for general guidance. NEVER attempt to open your boiler or perform complex repairs yourself. If you smell gas, suspect a leak, or are unsure, turn off your gas supply and call a Gas Safe engineer immediately.
Common Vaillant Boiler Fault Codes:
Here are some of the most frequently encountered Vaillant error codes:
1. F.22 – Low Water Pressure
This is a very common fault code indicating that your boiler’s water pressure is too low, or there isn’t enough water in the system. The boiler will typically lock out for safety
Water loss from the heating system (e.g., small leak in pipework, radiators, or boiler).
Pressure naturally dropping over time (very gradual).
Recently bled radiators.
Faulty pressure sensor (less common).
Locate the pressure gauge on your Vaillant boiler; it should typically be between 1 and 1.5 bar (when cold).
If low, you can often re-pressurise the system using the external or internal filling loop, following your Vaillant boiler’s specific manual instructions carefully.
If you repressurise the boiler and the F.22 code returns frequently, it suggests a leak in the system or a faulty component like the pressure sensor. This requires professional investigation.
2. F.28 – Ignition Unsuccessful / No Ignition
The boiler failed to ignite during startup. It’s attempting to light but can’t establish a flame.
No gas supply (e.g., gas meter valve closed, low gas pressure in the area).
Blocked condensate pipe (especially in cold weather, preventing gas ignition).
Faulty ignition electrode or ignition lead.
Issues with the gas valve.
Fan fault.
Ensure your gas supply is on and other gas appliances (like your hob) are working.
Check for a frozen condensate pipe outside your property (a white/grey plastic pipe, often near a drain). If frozen, you may be able to gently thaw it with warm water (consult your manual).
The F.28 code often points to a gas supply issue, ignition problem, or fan fault, all of which require a Gas Safe registered engineer for diagnosis and repair.
3. F.29 – Flame Loss During Operation / Re-ignition Unsuccessful
The boiler ignited successfully, but the flame then extinguished during operation and failed to re-ignite.
Interruption to the gas supply.
Faulty flue system (not clearing combustion products effectively).
Problem with the gas valve.
Faulty electrode or PCB (Printed Circuit Board).
Low gas pressure.
Ensure your main gas supply is definitely on.
This is a critical safety fault related to the flame and gas supply. Immediately call a Gas Safe registered engineer.
4. F.75 – Pressure Sensor and/or Pump Fault
The boiler isn’t detecting a sufficient pressure change when the pump starts operating. This usually indicates an issue with the water pressure sensor or the pump itself.
Faulty or blocked water pressure sensor.
Malfunctioning or stuck pump.
Air trapped in the system (less common, but can affect pressure readings).
Rarely, issues with the PCB.
Check your boiler pressure (should be 1-1.5 bar). If it’s low, try topping it up (as with F.22) and then try resetting the boiler.
Listen carefully for your boiler pump trying to start (a hum or vibration).
This is a complex fault that often requires testing and potentially replacing the pressure sensor or the pump. An experienced Gas Safe engineer is needed.
5. F.61 / F.62 – Gas Valve Actuation Fault / Gas Valve Delay
These codes indicate a problem with the gas valve or its control. The boiler’s electronics are having trouble opening or closing the gas valve correctly.
Faulty gas valve assembly.
Wiring harness issue to the gas valve.
Problem with the main PCB.
There are no safe user checks for this fault.
These are serious internal gas system faults that must be diagnosed and repaired by a Gas Safe registered engineer only.
6. F.72 – Flow/Return Sensor Deviation
There’s a significant and implausible temperature difference between the flow and return temperature sensors. The sensors are giving conflicting readings.
Faulty flow or return temperature sensor (NTC).
Circulation issues (e.g., a blocked pump, air in the system, blockage in pipework).
Wiring issue to the sensors.
Ensure all radiator valves are open.
You can try bleeding radiators to remove trapped air.
This often requires professional diagnosis to determine if it’s a sensor fault, a circulation problem, or a more serious internal blockage.