GAS BOILER ERROR CODES
Troubleshooting Your Combi Boiler
When it comes to gas boilers, the family-owned German-based company Vaillant are market leaders, producing a range of combination, regular and system gas boilers for heating and supplying hot water that are popular in Britain.
However good a boiler may be however, they are not invincible and boiler breakdown is always an unpleasant threat that looms if your boiler develops a fault.
Vaillant have made it easier to diagnose the problem with your gas boiler by providing its appliances with built-in error codes (or fault codes) to alert you to specific issues. Each error code indicates what the fault is, so it’s wise to make sure you know what the codes mean.
Most gas boiler faults can only be rectified by a qualified gas-safe registered engineer, so although you can use these Vaillant boiler error codes as a guide, its best to call in a professional to attend to your faulty Vaillant boiler.
Prestige Services provide first class gas boiler repairs across the Cotswolds, North Wiltshire and West Oxfordshire – so if you see an error code on your boiler’s display panel get in touch.
We’ve put together this handy guide to help you identify what some of the most commonly seen Vaillant Combi gas boiler codes mean on the latest Vaillant Combi boiler models.
Flow temperature sensor faulty or not connected
Return temperature sensor faulty or not connected
Flow temperature sensor faulty or has short-circuited
Return temperature sensor faulty or has short-circuited
Maximum temperature at the flow/return temperature sensor is too high when the safety cut out function is operating using the Negative Temperature Coefficient (NTC)
No/insufficient water because the water pressure is too low
Temperature spread is too great and/or water circulation too low
Safety switch-off: Temperature increase too fast
Safety switch-off: Flue gas temperature too high
Gas valve assembly stepper motor faulty or not connected
Safety switch-off: Monitoring electrode reports an incorrect flame
Failure during start-up or ignition unsuccessful. Gas pressure monitor or thermal cut-out has been triggered
Gas supply interrupted intermittently. Re-ignition failed
Fan faulty or not connected
Undervoltage on the eBUS (Vaillant communication system)
The gas valve assembly cannot be actuated
Delayed switch-off sequence for the gas valve after the flame is extinguished
EEPROM (Electronic controls in the system) are faulty
Electronics, safety-relevant sensor or cable faulty
Electronics faulty or too hot due to external influences
Implausible flame signal
Flame monitor reports an unstable flame signal
Incorrect/missing Device Specific Number or incorrect/missing coding resistor
Flow temperature sensor returns implausible values
Temperature difference between flow and return temperature sensor is too great
Water pressure sensor reports that the water pressure is too low
Water pressure too high
Insufficient pressure jump detected when starting the pump
No flue non-return flap feedback; condensate pump over flow
UK link box is connected without the domestic hot water temperature sensor being bridged
Temperature difference between flow and return temperature sensor is too small
Temperature difference is implausible
Flow/return temperature sensors returning incorrect/implausible values
Flow temperature sensor defective or not connected
Return temperature sensor faulty or not connected
Cylinder temperature sensor for the shift-load cylinder defective or not connected
Temperature sensor for the shift-load cylinder defective or not connected
Flow temperature sensor defective or has short-circuited
Return temperature sensor faulty or has short-circuited
Cylinder temperature sensor defective or has short-circuited
Short circuit in the Cylinder sensor. The Warm start sensor/cylinder temperature sensor is defective or not connected
Maximum temperature at the flow/return temperature sensor is too high when the safety cut- out function is operating using the NTC (negative temperature coefficient)
Safety cut out because there is no/insufficient water in the product or the water pressure is too low
Safety switch-off due to the temperature spread being too great or water circulation too low
Safety switch-off because temperature increase is too fast
Safety switch-off because the flue gas temperature too high
Gas valve assembly stepper motor defective or not connected
Safety switch-off because the monitoring electrode reports an incorrect flame
Failure during start-up or ignition unsuccessful. Gas pressure monitor or thermal cut-out has been triggered
Gas supply interrupted intermittently. Reignition failed
Fan defective or not connected
Coding resistor or gas group resistor has caused a short circuit
Undervoltage on the eBUS
Mass flow sensor defective or not connected
Mass flow sensor faulty 22
No gas inlet pressure or insufficient gas inlet pressure causes faults when the appliance is started
All-gas sensor defective or has short-circuited
Safety shutdown after the CO limit value is exceeded
Regulation fault caused by corroded ignition electrode
The gas valve assembly cannot be actuated
Delayed switch-off sequence for the gas valve after the flame is extinguished
EEPROM faulty
Electronics, safety-relevant sensor or cable is defective
Electronics defective or overheated due to external influences
Implausible flame signal
Flame monitor reports an unstable flame signal
Incorrect/missing Device Specific Number or incorrect/missing coding resistor
Flow temperature sensor returns implausible values
Temperature difference between flow and return temperature sensor is too great
Water pressure sensor reports that the water pressure is too low
Water pressure too high
Insufficient pressure jump detected when starting the pump
No flue non-return flap feedback; condensate pump over flow
UK link box is connected without the domestic hot water temperature sensor being bridged
Inlet temperature sensor faulty or not connected
Cylinder is not fully charged after specified time
External current anode defective or not connected
Temperature difference between flow and return temperature sensor is too small
Temperature difference is implausible
Flow/return temperature sensors returning incorrect/implausible values
Communication fault with actoSTOR interrupted
Sensor on the actoSTOR is defective
Combustion quality outside the permitted range
Sensors return implausible values
Flow temperature sensor defective or not connected
Return temperature sensor faulty or not connected
Flow temperature sensor defective or has short-circuited
Return temperature sensor faulty or has short-circuited
Cylinder temperature sensor defective or has short-circuited
Short circuit in the Cylinder sensor. The Warm start sensor/cylinder temperature sensor is defective or not connected
Maximum temperature at the flow/return temperature sensor is too high when the safety cut- out function is operating using the NTC (negative temperature coefficient)
Safety cut out because there is no/insufficient water in the product or the water pressure is too low
Safety switch-off due to the temperature spread being too great or water circulation too low
Safety switch-off because temperature increase is too fast
Safety switch-off because the flue gas temperature too high
Safety switch-off because the monitoring electrode reports an incorrect flame
Failure during start-up or ignition unsuccessful. Gas pressure monitor or thermal cut-out has been triggered
Fan defective or not connected
Undervoltage on the eBUS
The gas valve assembly cannot be actuated
Delayed switch-off sequence for the gas valve after the flame is extinguished
Electronics, safety-relevant sensor or cable is defective
Electronics defective or overheated due to external influences
Implausible flame signal
Flame monitor reports an unstable flame signal
Incorrect/missing Device Specific Number or incorrect/missing coding resistor
Flow temperature sensor returns implausible values
Temperature difference between flow and return temperature sensor is too great
Water pressure sensor reports that the water pressure is too low
Water pressure too high
Insufficient pressure jump detected when starting the pump
No flue non-return flap feedback; condensate pump over flow
Fault: Condensate or smoke
UK link box is connected without the domestic hot water temperature sensor being bridged
Temperature difference between flow and return temperature sensor is too small
Temperature difference is implausible
Flow/return temperature sensors returning incorrect/implausible values
Fault: Underfloor heating contact
Fault: Electrodes
Fault: Gas valve
Fault: Pump
Flow temperature sensor defective or not connected
Return temperature sensor faulty or not connected
Cylinder temperature sensor for the shift-load cylinder defective or not connected
Temperature sensor for the shift-load cylinder defective or not connected
Flow temperature sensor defective or has short-circuited
Return temperature sensor faulty or has short-circuited
Cylinder temperature sensor defective or has short-circuited
Short circuit in the Cylinder sensor. The Warm start sensor/cylinder temperature sensor is defective or not connected
Maximum temperature at the flow/return temperature sensor is too high when the safety cut- out function is operating using the NTC (negative temperature coefficient)
Safety cut out because there is no/insufficient water in the product or the water pressure is too low
Safety switch-off due to the temperature spread being too great or water circulation too low
Safety switch-off because temperature increase is too fast
Safety switch-off because the flue gas temperature too high
Gas valve assembly stepper motor defective or not connected
Safety switch-off because the monitoring electrode reports an incorrect flame
Failure during start-up or ignition unsuccessful. Gas pressure monitor or thermal cut-out has been triggered
Gas supply interrupted intermittently. Reignition failed
Fan defective or not connected
Pressure switch
Fault: Air/flue gas duct
Coding resistor or gas group resistor has caused a short circuit
Undervoltage on the eBUS
All-gas sensor defective or has short-circuited
Safety shutdown after the CO limit value is exceeded
Regulation fault caused by corroded ignition electrode
The gas valve assembly cannot be actuated
Delayed switch-off sequence for the gas valve after the flame is extinguished
EEPROM faulty
Electronics, safety-relevant sensor or cable is defective
Electronics defective or overheated due to external influences
Implausible flame signal
Flame monitor reports an unstable flame signal
Incorrect/missing Device Specific Number or incorrect/missing coding resistor
Flow temperature sensor returns implausible values
Temperature difference between flow and return temperature sensor is too great
Water pressure sensor reports that the water pressure is too low
Water pressure too high
Insufficient pressure jump detected when starting the pump
No flue non-return flap feedback; condensate pump over flow
Inlet temperature sensor faulty or not connected
Cylinder is not fully charged after specified time
External current anode defective or not connected
Temperature difference between flow and return temperature sensor is too small
Temperature difference is implausible
Flow/return temperature sensors returning incorrect/implausible values
Communication fault with actoSTOR interrupted
Sensors return implausible values
If you have any other type, make or model of Vaillant boiler which is not working properly and/or displaying an error code, feel free to contact us at Prestige Services for advice and assistance. We cover a wide range of locations in southern England.
I hope you find our web site useful, should you have any questions please feel free to call me on: