BoilerFaultCodes d.0
Your boiler is currently operating normally and is simply indicating that it is running at a lower workload to maintain your desired temperature.
Vaillant ecoMAX 622 Fault codes & diagnostics
36 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
System Natural Gas 22 kW 2000-2005 Discontinued
Replaced by: ecoTEC plus 624
The fault code is already on your display
Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →
Severity at a glance
Each cell = one fault code. Hover to identify. 1 Emergency
29 High
2 Medium
4 Low
Just want the most common Vaillant ecoMAX 622 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes
All 36 documented codes
Tap any card for details
d.1 Your boiler is currently running its internal pump to move leftover warm water away from the heat exchanger to prevent overheating, which is a normal part of its cooling cycle.
Your boiler is currently running its internal pump to move leftover warm water away from the heat exchanger to prevent overheating, which is a normal part of its cooling cycle.
Parts commonly replaced
- Pump
- Printed Circuit Board
Related codes
d.2 Your boiler is currently in a forced waiting period to prevent it from cycling on and off too frequently, which is usually a normal part of its operation.
Your boiler is currently in a forced waiting period to prevent it from cycling on and off too frequently, which is usually a normal part of its operation.
Related codes
d.14 Your boiler is struggling to circulate water effectively because the internal pump is not running at the speed it needs to.
Your boiler is struggling to circulate water effectively because the internal pump is not running at the speed it needs to.
Parts commonly replaced
- Central heating pump
- Printed Circuit Board (PCB)
Related codes
d.16 Your boiler is struggling to signal the external pump responsible for circulating warmth to your radiators, meaning your heating system may stop working properly.
Your boiler is struggling to signal the external pump responsible for circulating warmth to your radiators, meaning your heating system may stop working properly.
Parts commonly replaced
- External central heating pump
- Wiring loom
- Main PCB
Related codes
d.71 Your boiler is limiting the maximum temperature it allows for the water circulating through your radiators to prevent the system from getting too hot.
Your boiler is limiting the maximum temperature it allows for the water circulating through your radiators to prevent the system from getting too hot.
What to check first
- Check the thermostat settings to ensure the target temperature is correct
- Navigate to the boiler control panel dial for maximum flow temperature
- Adjust the flow temperature setting if it has been accidentally set too low
Parts commonly replaced
- NTC sensor
- Main PCB
d.72 Your boiler is struggling to circulate water correctly after it has finished heating your water or home, which can often be caused by a sensor misreading or a temporary blockage.
Your boiler is struggling to circulate water correctly after it has finished heating your water or home, which can often be caused by a sensor misreading or a temporary blockage.
Parts commonly replaced
- NTC temperature sensor
- Pump
- Printed Circuit Board
Related codes
d.73 Your boiler is struggling to accurately measure or maintain the temperature of the water used for your taps.
Your boiler is struggling to accurately measure or maintain the temperature of the water used for your taps.
Parts commonly replaced
- NTC temperature sensor
- Printed Circuit Board (PCB)
Related codes
F.0 Your boiler has lost connection with its main internal temperature sensor, meaning it cannot safely tell how hot the water is and has shut down as a precaution.
Your boiler has lost connection with its main internal temperature sensor, meaning it cannot safely tell how hot the water is and has shut down as a precaution.
Parts commonly replaced
- Flow NTC Thermistor
- Sensor wiring harness
Related codes
F.00 Your boiler has lost the signal from the sensor that monitors the temperature of the water leaving the unit, so it has shut down to prevent overheating.
Your boiler has lost the signal from the sensor that monitors the temperature of the water leaving the unit, so it has shut down to prevent overheating.
Parts commonly replaced
- Flow NTC sensor
- Wiring harness
Related codes
Showing 11–20 of 36
F.1 Your boiler has stopped working because it cannot correctly measure the temperature of the water returning to the unit due to a faulty sensor or connection.
Your boiler has stopped working because it cannot correctly measure the temperature of the water returning to the unit due to a faulty sensor or connection.
Parts commonly replaced
- Return NTC thermistor
- Wiring harness
Related codes
F.01 Your boiler has lost the signal from one of its internal temperature sensors, causing it to shut down for safety because it cannot accurately monitor the system heat.
Your boiler has lost the signal from one of its internal temperature sensors, causing it to shut down for safety because it cannot accurately monitor the system heat.
Parts commonly replaced
- Return NTC sensor
- Wiring harness
Related codes
F.10 Your boiler has stopped working because a sensor that monitors water temperature has developed an electrical fault.
Your boiler has stopped working because a sensor that monitors water temperature has developed an electrical fault.
Parts commonly replaced
- Flow NTC thermistor
- NTC sensor wiring harness
Related codes
F.11 Your boiler has stopped working because one of its internal temperature sensors has developed an electrical fault and is giving an incorrect reading.
Your boiler has stopped working because one of its internal temperature sensors has developed an electrical fault and is giving an incorrect reading.
Parts commonly replaced
- Return NTC thermistor
- Wiring harness/connector
Related codes
F.13 Your boiler has lost connection to the hot water cylinder sensor, meaning it cannot tell how hot your water is or when to heat it.
Your boiler has lost connection to the hot water cylinder sensor, meaning it cannot tell how hot your water is or when to heat it.
Parts commonly replaced
- NTC Cylinder Sensor
- Wiring Loom/Harness
Related codes
F.20 Your boiler has switched itself off because it has reached an unsafe temperature and needs to cool down before it can restart.
Your boiler has switched itself off because it has reached an unsafe temperature and needs to cool down before it can restart.
What to check first
- Check that your radiator valves are fully open to allow water to flow.
- Ensure there is enough water pressure in the system (typically 1.0 to 1.5 bar).
- Press the 'Reset' button (flame symbol with a cross) once the boiler has cooled down.
Parts commonly replaced
- Circulation Pump
- Overheat Thermostat
- NTC Temperature Sensor
Related codes
F.22 Your boiler has detected that there is not enough water pressure in the system to operate safely.
Your boiler has detected that there is not enough water pressure in the system to operate safely.
What to check first
- Check the pressure gauge on the front of the boiler or under the casing.
- Locate the external filling loop (braided silver hose) usually found beneath the boiler.
- Slowly open the valves until the pressure gauge reaches between 1.0 and 1.5 bar, then close them tightly.
Parts commonly replaced
- Circulation Pump
- Pressure Sensor
- Pump Lead
Related codes
F.23 Your boiler is struggling to circulate water properly, often because the system pressure is too low or there is trapped air preventing the heat from moving away from the boiler.
Your boiler is struggling to circulate water properly, often because the system pressure is too low or there is trapped air preventing the heat from moving away from the boiler.
What to check first
- Check the pressure gauge and top up to 1.5 bar using the filling loop if it is too low
- Bleed your radiators to remove any trapped air from the system
- Ensure all radiator valves are fully open and not stuck
Parts commonly replaced
- Circulation pump
- NTC Temperature Sensors
- Automatic air vent
Related codes
F.24 Your boiler is overheating because water isn't moving through the system quickly enough to take the heat away.
Your boiler is overheating because water isn't moving through the system quickly enough to take the heat away.
What to check first
- Check the pressure gauge and top up the system to 1.5 bar if it is too low
- Ensure all radiator valves are fully open
- Bleed your radiators and the pump to remove trapped air
Parts commonly replaced
- Circulation Pump
- Flow/Return NTC Thermistor
- System Pressure Sensor
Related codes
F.25 Your boiler has detected that the water pressure has dropped too low or there is a problem with the internal sensor that monitors it, causing the system to shut down for safety.
Your boiler has detected that the water pressure has dropped too low or there is a problem with the internal sensor that monitors it, causing the system to shut down for safety.
What to check first
- Check the central heating pressure gauge; it should ideally be between 1.0 and 1.5 bar.
- If the pressure is below 1.0 bar, use the external filling loop to top up the system until the gauge reaches the correct level.
- Restart the boiler to see if the fault clears.
Parts commonly replaced
- Water pressure switch
- Wiring harness / plug connector
Related codes
Showing 21–30 of 36
F.27 Your boiler has detected a signal error between its control system and gas supply, preventing it from lighting safely.
Your boiler has detected a signal error between its control system and gas supply, preventing it from lighting safely.
Parts commonly replaced
- Main PCB (Printed Circuit Board)
- Gas Valve
- Ignition Electrodes
Related codes
F.28 Your boiler has failed to ignite, which means it cannot light the gas flame required to provide heat or hot water.
Your boiler has failed to ignite, which means it cannot light the gas flame required to provide heat or hot water.
What to check first
- Check if other gas appliances in your home, such as a hob, are working to ensure gas is reaching the property.
- If you have a pre-payment meter, check that you have remaining credit.
- Ensure your gas stopcock is fully open.
- Press the reset button (indicated by a flame with a line through it) for one second.
Parts commonly replaced
- Ignition Electrode
- Gas Valve
- Ignition Lead
- Spark Generator
Related codes
F.29 Your boiler has lost its gas supply or the flame has gone out and it cannot restart itself.
Your boiler has lost its gas supply or the flame has gone out and it cannot restart itself.
What to check first
- Check if other gas appliances in your home, like a hob, are working correctly.
- If you have a prepayment meter, ensure you have sufficient credit topped up.
- Check if the gas emergency control valve near your meter has been accidentally turned off.
- Press the 'Reset' button (flame symbol with a cross) for one second to see if the boiler restarts.
Parts commonly replaced
- Gas Valve
- Ignition Electrode
- Ignition Lead
- PCB
Related codes
F.32 Your boiler's fan is struggling to spin at the correct speed, which prevents the unit from starting up safely to heat your home.
Your boiler's fan is struggling to spin at the correct speed, which prevents the unit from starting up safely to heat your home.
Parts commonly replaced
- Fan assembly
- Printed Circuit Board (PCB)
- Wiring harness
F.41 Your boiler has lost its electronic connection to the gas control valve, meaning it cannot safely release fuel to start the flame.
Your boiler has lost its electronic connection to the gas control valve, meaning it cannot safely release fuel to start the flame.
Parts commonly replaced
- Gas Valve
- Main PCB (Printed Circuit Board)
- Wiring Harness
Related codes
F.42 Your boiler's electronic control panel is unable to identify the specific model of boiler it is supposed to be operating due to an electrical connection fault.
Your boiler's electronic control panel is unable to identify the specific model of boiler it is supposed to be operating due to an electrical connection fault.
Parts commonly replaced
- Wiring harness
- Coding resistor
- PCB (Printed Circuit Board)
Related codes
F.43 Your boiler's control board cannot identify which model it is supposed to be, causing it to shut down for safety.
Your boiler's control board cannot identify which model it is supposed to be, causing it to shut down for safety.
Parts commonly replaced
- Main PCB (Printed Circuit Board)
- Boiler Coding Resistor
Related codes
F.60 Your boiler has detected an electrical fault with the part that controls the gas supply, meaning it cannot ignite safely for heating or hot water.
Your boiler has detected an electrical fault with the part that controls the gas supply, meaning it cannot ignite safely for heating or hot water.
Parts commonly replaced
- Gas valve assembly
- Main PCB (Printed Circuit Board)
- Wiring harness
Related codes
F.61 Your boiler has detected an electrical problem with the system that controls the gas flow, meaning it cannot light safely for heating or hot water.
Your boiler has detected an electrical problem with the system that controls the gas flow, meaning it cannot light safely for heating or hot water.
Parts commonly replaced
- Gas valve assembly
- PCB (Main control board)
- Wiring harness
Related codes
F.62 Your boiler has detected that the gas valve is not closing properly or there is a communication error between the gas valve and the control board.
Your boiler has detected that the gas valve is not closing properly or there is a communication error between the gas valve and the control board.
Parts commonly replaced
- Gas valve assembly
- Printed Circuit Board (PCB)
Related codes
Showing 31–36 of 36
F.63 Your boiler's internal computer brain has developed a memory error and cannot process the instructions needed to run safely.
Your boiler's internal computer brain has developed a memory error and cannot process the instructions needed to run safely.
Parts commonly replaced
- Main Printed Circuit Board (PCB)
Related codes
F.64 Your boiler has detected an electrical issue with its internal heat sensors or the main control board, preventing it from heating your home safely.
Your boiler has detected an electrical issue with its internal heat sensors or the main control board, preventing it from heating your home safely.
Parts commonly replaced
- Flow NTC sensor
- Return NTC sensor
- Main PCB (Printed Circuit Board)
Related codes
F.65 Your boiler's internal control board has become too hot to operate safely and has shut down to prevent damage.
Your boiler's internal control board has become too hot to operate safely and has shut down to prevent damage.
Parts commonly replaced
- Main Printed Circuit Board (PCB)
- Internal Heat Shield
Related codes
F.67 Your boiler has detected a flame when there shouldn't be one, or has a confusion in its internal electronics, causing it to shut down for safety.
Your boiler has detected a flame when there shouldn't be one, or has a confusion in its internal electronics, causing it to shut down for safety.
Parts commonly replaced
- Printed Circuit Board (PCB)
- Ignition Electrode
- Flame Sensing Electrode
Related codes
F.70 Your boiler's electronic brains are essentially having a communication breakdown and don't recognize each other, causing the unit to stop working for safety.
Your boiler's electronic brains are essentially having a communication breakdown and don't recognize each other, causing the unit to stop working for safety.
Parts commonly replaced
- Main Printed Circuit Board (PCB)
- Display/User Interface Board
Related codes
F.75 Your boiler has sensed that the pump is running but the water isn't moving through the system properly, causing it to shut down to prevent damage.
Your boiler has sensed that the pump is running but the water isn't moving through the system properly, causing it to shut down to prevent damage.
What to check first
- Check the pressure gauge on the front of the boiler; it should be between 1.0 and 1.5 bar.
- If the pressure is too low, use the external filling loop to top up the system water.
- Ensure all radiator valves and internal isolation valves are fully open.
Parts commonly replaced
- Water Pressure Sensor
- Circulation Pump
- Expansion Vessel
Related codes
Status & diagnostic codes 30 operating states & engineer diagnostics
Not faults — these are normal operating states. Tap to expand.
30 operating states & engineer diagnostics
Not faults — these are normal operating states. Tap to expand.
S.0 Status Your boiler is working correctly but is currently idle because it hasn't been told to turn on by your thermostat or timer. S.1 Status Your boiler is currently working as normal to pump heat through your radiators and does not have a fault. S.2 Status Your boiler is preparing to heat your home and is checking that water is moving through the pipes before it lights the burner. S.3 Status Your boiler is currently trying to start the ignition process to provide heating, which is a normal part of the startup sequence and not necessarily a fault unless it remains stuck on this screen. S.4 Status Your boiler is operating normally and is currently in the process of heating your radiators. S.5 Status Your boiler is currently cooling itself down after a heating cycle and will resume normal operation shortly. S.6 Status Your boiler is trapped in a cooling-down cycle where the fan keeps running longer than necessary, preventing it from starting a new heating cycle. S.7 Status Your boiler is temporarily keeping the internal pump running to safely cool down the heat exchanger after a period of heating. S.8 Status Your boiler is taking a short rest to prevent it from switching on and off too frequently, which helps save energy and protect its internal components. S.10 Status Your boiler is simply indicating that it is currently working to heat your hot water tank as requested. S.11 Status Your boiler is currently working as it should to heat up your hot water tank. S.13 Status Your boiler is currently going through the normal steps to start the ignition process for your hot water. S.14 Status Your boiler is currently working correctly and is providing heat to your hot water tank as intended. S.16 Status Your boiler's fan is staying on for longer than usual to cool the internal components after providing hot water. S.17 Status Your boiler is briefly keeping the pump running to dissipate excess heat after heating your hot water, which is a normal operational status rather than a breakdown. S.20 Status Your boiler is simply indicating that it is currently pre-heating itself to ensure hot water is available quickly when you need it. S.21 Status Your boiler is currently preparing itself to provide hot water quickly and is not actually reporting a fault. S.23 Status Your boiler is currently preparing to fire up the burners to heat your water or radiators after a brief pause. S.24 Status Your boiler is performing a routine start-up process to keep its internal water warm and is not actually experiencing a fault. S.26 Status Your boiler is staying in a cooling-down mode because the internal fan is running for longer than it should after heating your water. S.27 Status Your boiler is briefly running its internal pump to circulate water and manage heat after it has been turned off, which is a normal operating state rather than a breakdown. S.28 Status Your boiler is taking a short, planned break to prevent it from turning on and off too frequently, which helps protect the internal components and improve efficiency. S.30 Status Your boiler is working fine, but it is currently waiting for your thermostat or programmer to tell it to turn on. S.32 Status Your boiler is pausing because its internal fan is not reaching the correct speed required to safely start the heating process. S.34 Status Your boiler is not broken; it has simply noticed the temperature is very cold and is running the pump or burner automatically to prevent the internal pipes from freezing. S.36 Status Your boiler is working fine but it is not receiving a signal from your thermostat or timer to turn the heating on. S.37 Status Your boiler is temporarily pausing because the fan speed is not within the required range for a safe startup. S.39 Status Your boiler has paused because it detected that the water temperature is too high for your underfloor heating system, triggered by a safety safety switch to protect your floors. S.53 Status Your boiler has temporarily paused its operation because it senses there is not enough water flowing through the system to heat your home safely. S.54 Status Your boiler has paused because it cannot detect enough water flow or pressure to operate safely without overheating.