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
Boiler locks out with F1 on display, burner does not ignite
Ignition Failure / No Flame Detection
F10
Boiler shows F10, no burner operation
Low Water Pressure / Water Shortage
F11
Boiler intermittently shows F11, especially during hot water demand
Flow Sensor / DHW Sensor Fault
F12
Boiler shows 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 shows F14, burner does not start, display may show low voltage warning
Mains Voltage / Power Supply Fault
F2
Boiler shows F2 and shuts down shortly after ignition attempt
Flame Loss During Operation
F20
Boiler displays F20, burner shuts down, pump may continue
Primary Circuit Overtemperature
F22
Boiler shows 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 shows F24, rapid temperature rise on display, then shutdown
Low Water Flow / Pump Protection
F28
Boiler locks out with F28 during ignition attempts, clicking heard but no flame
Ignition Lockout / No Gas Ignition
F29
Boiler shows F29 after running briefly, then flame goes out
Flame Loss During Operation
F3
Boiler displays F3 and will not start, 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 shows F37, pressure fluctuates or drops during operation
Water Pressure Too Low / Unstable
F4
Boiler shows F4, burner does not start, fan may not run
Fan / Air Pressure Fault
F41
Boiler displays F41, burner output limited, poor heating performance
Flow Temperature Rise Too Fast
F49
Boiler shows F49, communication or low-voltage error, may affect controls
Low Voltage / Bus Short Circuit
F5
Boiler locks out with F5, no ignition, fan may run continuously
Air Pressure Switch / Flue Blockage Fault
F6
Boiler shows F6, heating and hot water disabled
Flow Temperature Sensor Fault
F61
Boiler locks out with F61, gas valve error indicated
Gas Valve Control Fault
F62
Boiler shows F62, may indicate gas valve closing delay
Gas Valve Shutoff Delay
F7
Boiler displays F7, 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
Boiler shows F8, burner stops, pump may continue running
Overheat Thermostat / Safety Temperature Limiter Trip
F83
Boiler shows F83, especially after filling or during start-up
Flow Sensor Temperature Rise Too Slow / Air in System
F84
Boiler displays F84, inconsistent flow/return readings
Flow and Return Sensor Mismatch
F85
Boiler shows F85, both flow and return sensors implausible
Dual Sensor Fault / Common Wiring Error
F9
Boiler locks out with F9, no heating or hot water
Gas Valve / Modulation Fault
F90
Boiler displays F90, burner does not start, communication error 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 leaking water from underneath the casing
Internal Water Leak
Symptom
Boiler making loud banging or knocking noises during operation (kettling)
Heat Exchanger Kettling / Localised Boiling
Symptom
Boiler pressure rises rapidly when heating, then discharges water outside
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
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 but heating works normally (combi boiler)
DHW Priority / Diverter Valve Fault
Symptom
Radiators not heating properly even though boiler runs
Poor Circulation / System Imbalance
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| F1 |
Boiler locks out with F1 on display, burner does not ignite
|
Ignition Failure / No Flame Detection | View Details |
| F10 |
Boiler shows F10, no burner operation
|
Low Water Pressure / Water Shortage | View Details |
| F11 |
Boiler intermittently shows F11, especially during hot water demand
|
Flow Sensor / DHW Sensor Fault | View Details |
| F12 |
Boiler shows 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 shows F14, burner does not start, display may show low voltage warning
|
Mains Voltage / Power Supply Fault | View Details |
| F2 |
Boiler shows F2 and shuts down shortly after 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 shows 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 shows 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 heard but no flame
|
Ignition Lockout / No Gas Ignition | View Details |
| F29 |
Boiler shows F29 after running briefly, then flame goes out
|
Flame Loss During Operation | View Details |
| F3 |
Boiler displays F3 and will not start, 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 shows F37, pressure fluctuates or drops during operation
|
Water Pressure Too Low / Unstable | View Details |
| F4 |
Boiler shows F4, burner does not start, fan may not run
|
Fan / Air Pressure Fault | View Details |
| F41 |
Boiler displays F41, burner output limited, poor heating performance
|
Flow Temperature Rise Too Fast | View Details |
| F49 |
Boiler shows F49, communication or low-voltage error, may affect controls
|
Low Voltage / Bus Short Circuit | View Details |
| F5 |
Boiler locks out with F5, no ignition, fan may run continuously
|
Air Pressure Switch / Flue Blockage Fault | View Details |
| F6 |
Boiler shows F6, heating and hot water disabled
|
Flow Temperature Sensor Fault | View Details |
| F61 |
Boiler locks out with F61, gas valve error indicated
|
Gas Valve Control Fault | View Details |
| F62 |
Boiler shows F62, may indicate gas valve closing delay
|
Gas Valve Shutoff Delay | View Details |
| F7 |
Boiler displays F7, 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 |
Boiler shows F8, burner stops, pump may continue running
|
Overheat Thermostat / Safety Temperature Limiter Trip | View Details |
| F83 |
Boiler shows F83, especially after filling or during start-up
|
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 shows F85, both flow and return sensors implausible
|
Dual Sensor Fault / Common Wiring Error | View Details |
| F9 |
Boiler locks out with F9, no heating or hot water
|
Gas Valve / Modulation Fault | View Details |
| F90 |
Boiler displays F90, burner does not start, communication error 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 leaking water from underneath the casing
|
Internal Water Leak | View Details |
| – |
Boiler 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 outside
|
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
|
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 but heating works normally (combi boiler)
|
DHW Priority / Diverter Valve Fault | View Details |
| – |
Radiators not heating properly even though boiler runs
|
Poor Circulation / System Imbalance | View Details |
No matching codes found
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