Viessmann Boilers Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
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F1
The boiler locks out with F1 on the display, and the burner does not ignite.
Ignition Failure / No Flame Detection
F10
Boiler displays F10, no burner operation.
Low Water Pressure / Water Shortage
F11
Boiler intermittently displays F11, especially during hot water demand.
Flow Sensor / DHW Sensor Fault
F12
Boiler displays F12, no response to thermostat demand.
Communication Fault with Room Controller / Bus
F13
Boiler displays F13, may still operate in limited mode.
Outdoor Temperature Sensor Fault
F14
Boiler displays F14, burner does not start, display may show low voltage warning.
Mains Voltage / Power Supply Fault
F2
The boiler displays F2 and shuts down shortly after an ignition attempt.
Flame Loss During Operation
F20
Boiler displays F20, burner shuts down, pump may continue.
Primary Circuit Overtemperature
F22
Boiler displays F22, no heating or hot water, pressure gauge low.
Dry Fire / Low Water Content
F23
Boiler displays F23, may cycle frequently, radiators unevenly warm.
Flow/Return Temperature Spread Too High
F24
Boiler displays F24, rapid temperature rise on display, then shutdown.
Low Water Flow / Pump Protection
F28
Boiler locks out with F28 during ignition attempts; clicking is heard but no flame.
Ignition Lockout / No Gas Ignition
F29
Boiler displays F29 after running briefly, then the flame goes out.
Flame Loss During Operation
F3
The boiler displays F3 and will not start; the fan may run briefly.
Flue Gas Temperature Sensor Fault
F32
Boiler displays F32, fan speed abnormal or not detected.
Fan Speed / Hall Sensor Fault
F37
Boiler displays F37; pressure fluctuates or drops during operation.
Water Pressure Too Low / Unstable
F4
The boiler displays F4, the burner does not start, and the fan may not run.
Fan / Air Pressure Fault
F41
Boiler displays F41; burner output is limited, leading to poor heating performance.
Flow Temperature Rise Too Fast
F49
Boiler displays F49, indicating a communication or low-voltage error, which may affect controls.
Low Voltage / Bus Short Circuit
F5
The boiler locks out with F5, there is no ignition, and the fan may run continuously.
Air Pressure Switch / Flue Blockage Fault
F6
The boiler displays F6, and heating and hot water are disabled.
Flow Temperature Sensor Fault
F61
Boiler locks out with F61, indicating a gas valve error.
Gas Valve Control Fault
F62
Boiler displays F62, which may indicate a gas valve closing delay.
Gas Valve Shutoff Delay
F7
The boiler displays F7; it may overheat quickly or not fire at all.
Return Temperature Sensor Fault
F70
Boiler displays F70 after PCB replacement or firmware update.
Configuration / Parameter Mismatch
F8
The boiler displays F8, the burner stops, and the pump may continue running.
Overheat Thermostat / Safety Temperature Limiter Trip
F83
Boiler displays F83, especially after filling or during startup.
Flow Sensor Temperature Rise Too Slow / Air in System
F84
Boiler displays F84, inconsistent flow/return readings.
Flow and Return Sensor Mismatch
F85
Boiler displays F85; both flow and return sensors show implausible readings.
Dual Sensor Fault / Common Wiring Error
F9
The boiler locks out with F9, and there is no heating or hot water.
Gas Valve / Modulation Fault
F90
Boiler displays F90; burner does not start, and a communication error is indicated.
Communication Fault Between Control Units
Symptom
Boiler and pipework vibrate or make humming noises when running
Hydraulic Resonance / Pump or Flow Noise
Symptom
Boiler display works but does not respond to room thermostat demand
Control Signal / Thermostat Fault
Symptom
Boiler fan runs but burner does not ignite, no error code displayed
Pre-Ignition Sequence Stalled
Symptom
Boiler frequently loses pressure over days or weeks
Chronic System Water Loss
Symptom
Boiler frequently short cycles (turns on and off rapidly).
Short Cycling / Oversized Boiler or Control Issue
Symptom
Boiler is leaking water from underneath the casing.
Internal Water Leak
Symptom
Boiler is making loud banging or knocking noises during operation (kettling).
Heat Exchanger Kettling / Localised Boiling
Symptom
Boiler pressure rises rapidly when heating, then discharges water externally.
Expansion Vessel Failure / Overpressure
Symptom
Boiler runs but emits a strong smell of gas or combustion products
Combustion / Flue Integrity Fault
Symptom
Boiler will not start at all; no display or lights are present.
No Power / Dead Boiler
Symptom
Condensate dripping from flue joints or outside wall
Condensate / Flue Drainage Fault
Symptom
Hot water temperature fluctuates between hot and cold.
Unstable DHW Temperature Control
Symptom
No domestic hot water (DHW) but heating works normally (combi boiler).
DHW Priority / Diverter Valve Fault
Symptom
Radiators are not heating properly even though the boiler is running.
Poor Circulation / System Imbalance
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| F1 |
The boiler locks out with F1 on the display, and the burner does not ignite.
|
Ignition Failure / No Flame Detection | View Details |
| F10 |
Boiler displays F10, no burner operation.
|
Low Water Pressure / Water Shortage | View Details |
| F11 |
Boiler intermittently displays F11, especially during hot water demand.
|
Flow Sensor / DHW Sensor Fault | View Details |
| F12 |
Boiler displays F12, no response to thermostat demand.
|
Communication Fault with Room Controller / Bus | View Details |
| F13 |
Boiler displays F13, may still operate in limited mode.
|
Outdoor Temperature Sensor Fault | View Details |
| F14 |
Boiler displays F14, burner does not start, display may show low voltage warning.
|
Mains Voltage / Power Supply Fault | View Details |
| F2 |
The boiler displays F2 and shuts down shortly after an ignition attempt.
|
Flame Loss During Operation | View Details |
| F20 |
Boiler displays F20, burner shuts down, pump may continue.
|
Primary Circuit Overtemperature | View Details |
| F22 |
Boiler displays F22, no heating or hot water, pressure gauge low.
|
Dry Fire / Low Water Content | View Details |
| F23 |
Boiler displays F23, may cycle frequently, radiators unevenly warm.
|
Flow/Return Temperature Spread Too High | View Details |
| F24 |
Boiler displays F24, rapid temperature rise on display, then shutdown.
|
Low Water Flow / Pump Protection | View Details |
| F28 |
Boiler locks out with F28 during ignition attempts; clicking is heard but no flame.
|
Ignition Lockout / No Gas Ignition | View Details |
| F29 |
Boiler displays F29 after running briefly, then the flame goes out.
|
Flame Loss During Operation | View Details |
| F3 |
The boiler displays F3 and will not start; the fan may run briefly.
|
Flue Gas Temperature Sensor Fault | View Details |
| F32 |
Boiler displays F32, fan speed abnormal or not detected.
|
Fan Speed / Hall Sensor Fault | View Details |
| F37 |
Boiler displays F37; pressure fluctuates or drops during operation.
|
Water Pressure Too Low / Unstable | View Details |
| F4 |
The boiler displays F4, the burner does not start, and the fan may not run.
|
Fan / Air Pressure Fault | View Details |
| F41 |
Boiler displays F41; burner output is limited, leading to poor heating performance.
|
Flow Temperature Rise Too Fast | View Details |
| F49 |
Boiler displays F49, indicating a communication or low-voltage error, which may affect controls.
|
Low Voltage / Bus Short Circuit | View Details |
| F5 |
The boiler locks out with F5, there is no ignition, and the fan may run continuously.
|
Air Pressure Switch / Flue Blockage Fault | View Details |
| F6 |
The boiler displays F6, and heating and hot water are disabled.
|
Flow Temperature Sensor Fault | View Details |
| F61 |
Boiler locks out with F61, indicating a gas valve error.
|
Gas Valve Control Fault | View Details |
| F62 |
Boiler displays F62, which may indicate a gas valve closing delay.
|
Gas Valve Shutoff Delay | View Details |
| F7 |
The boiler displays F7; it may overheat quickly or not fire at all.
|
Return Temperature Sensor Fault | View Details |
| F70 |
Boiler displays F70 after PCB replacement or firmware update.
|
Configuration / Parameter Mismatch | View Details |
| F8 |
The boiler displays F8, the burner stops, and the pump may continue running.
|
Overheat Thermostat / Safety Temperature Limiter Trip | View Details |
| F83 |
Boiler displays F83, especially after filling or during startup.
|
Flow Sensor Temperature Rise Too Slow / Air in System | View Details |
| F84 |
Boiler displays F84, inconsistent flow/return readings.
|
Flow and Return Sensor Mismatch | View Details |
| F85 |
Boiler displays F85; both flow and return sensors show implausible readings.
|
Dual Sensor Fault / Common Wiring Error | View Details |
| F9 |
The boiler locks out with F9, and there is no heating or hot water.
|
Gas Valve / Modulation Fault | View Details |
| F90 |
Boiler displays F90; burner does not start, and a communication error is indicated.
|
Communication Fault Between Control Units | View Details |
| – |
Boiler and pipework vibrate or make humming noises when running
|
Hydraulic Resonance / Pump or Flow Noise | View Details |
| – |
Boiler display works but does not respond to room thermostat demand
|
Control Signal / Thermostat Fault | View Details |
| – |
Boiler fan runs but burner does not ignite, no error code displayed
|
Pre-Ignition Sequence Stalled | View Details |
| – |
Boiler frequently loses pressure over days or weeks
|
Chronic System Water Loss | View Details |
| – |
Boiler frequently short cycles (turns on and off rapidly).
|
Short Cycling / Oversized Boiler or Control Issue | View Details |
| – |
Boiler is leaking water from underneath the casing.
|
Internal Water Leak | View Details |
| – |
Boiler is making loud banging or knocking noises during operation (kettling).
|
Heat Exchanger Kettling / Localised Boiling | View Details |
| – |
Boiler pressure rises rapidly when heating, then discharges water externally.
|
Expansion Vessel Failure / Overpressure | View Details |
| – |
Boiler runs but emits a strong smell of gas or combustion products
|
Combustion / Flue Integrity Fault | View Details |
| – |
Boiler will not start at all; no display or lights are present.
|
No Power / Dead Boiler | View Details |
| – |
Condensate dripping from flue joints or outside wall
|
Condensate / Flue Drainage Fault | View Details |
| – |
Hot water temperature fluctuates between hot and cold.
|
Unstable DHW Temperature Control | View Details |
| – |
No domestic hot water (DHW) but heating works normally (combi boiler).
|
DHW Priority / Diverter Valve Fault | View Details |
| – |
Radiators are not heating properly even though the boiler is running.
|
Poor Circulation / System Imbalance | View Details |
No matching codes found
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