Vaillant Fault Codes

Select a fault code to see its meaning, common causes and how to fix it.

con The Con (sometimes shown as ConF or Con F) fault code on a Vaillant boiler signals that the main control board and the… Read more →
F.00 The F.00 fault code (sometimes shown as F.0 on older displays) tells you that the boiler's heating-flow NTC thermistor… Read more →
F.01 The F.01 code on a Vaillant boiler signals that the heating return NTC (Negative Temperature Coefficient) thermistor… Read more →
F.02 The F.02 code appears when your Vaillant boiler cannot get a reliable temperature reading from its flow NTC thermistor… Read more →
F.03 The F.03 code on a Vaillant boiler signals that the boiler's control unit has lost a valid reading from a key… Read more →
F.04 The F.04 fault code on Vaillant ecoTEC boilers signals that the control board has lost a valid reading from the heating… Read more →
F.05 The Vaillant F.05 fault code is a safety lock-out triggered when the boiler detects an abnormally high water… Read more →
F.06 The F.06 fault code on Vaillant boilers indicates that the boiler's control board is receiving an unreliable or… Read more →
F.10 The F.10 code on a Vaillant boiler indicates that the heating flow NTC thermistor — the sensor that monitors the… Read more →
F.11 The F.11 code appears on Vaillant boilers when the control board detects a short circuit in the flow NTC (Negative… Read more →
F.12 The F.12 code appears on Vaillant boilers when the appliance detects a blockage that is directly affecting system… Read more →
F.13 The F.13 code tells you that the boiler's control board has detected a short circuit on the cylinder temperature sensor… Read more →
F.14 The F.14 code appears on Vaillant boilers when the control board detects an interruption in the signal from the heating… Read more →
F.15 The F.15 code appears on Vaillant boilers when the appliance cannot confirm that water is circulating properly around… Read more →
F.17 The F.17 code appears on Vaillant boilers when the control board detects an electrical polarity problem. This usually… Read more →
F.20 The F.20 code appears when your Vaillant boiler detects that the water temperature at the flow or return NTC thermistor… Read more →
F.21 The F.21 code is Vaillant's safety lockout for what it calls a 'flame simulation' condition — meaning the boiler's… Read more →
F.22 F.22 is a low water pressure (system protection) fault. Your Vaillant boiler has detected that there isn't enough water… Read more →
F.23 The F.23 fault code appears on Vaillant boilers when the temperature gap between the flow pipe (hot water leaving the… Read more →
F.24 The F.24 code appears on Vaillant boilers when the PCB detects that water temperature is climbing too fast, almost… Read more →
F.25 The F.25 fault code on a Vaillant boiler indicates that the safety temperature limiter (overheat thermostat) has… Read more →
F.26 The F.26 fault code on Vaillant ecoTEC Pro and ecoTEC Plus boilers indicates a problem with the stepper motor that… Read more →
F.27 The F.27 code appears on Vaillant ecoTEC Pro and Plus boilers when the boiler's control system detects what it… Read more →
F.28 F.28 is an ignition lockout fault. Your Vaillant boiler ran through its normal start-up sequence but failed to detect a… Read more →
F.29 F.29 is a flame-failure lockout. It means your Vaillant boiler successfully lit but then lost the flame while running,… Read more →
F.32 The F.32 fault code on a Vaillant ecoTEC boiler indicates that the fan is not running at the correct speed or is… Read more →
F.33 The F.33 code appears on Vaillant boilers in two closely related scenarios. On ecoTEC models (including the popular… Read more →
F.35 The F.35 code appears on Vaillant boilers when the control system detects a problem with the air supply or flue gas… Read more →
F.37 The F.37 code appears on Vaillant boilers when the PCB detects that the fan is not spinning at the expected speed — or… Read more →
F.42 The F.42 code appears when your Vaillant boiler cannot correctly read its coding resistor — a small component… Read more →
F.43 The Vaillant F.43 fault code signals a gas group fault, meaning the boiler has detected that the ratio between the gas… Read more →
F.49 The F.49 code on a Vaillant boiler signals a fault within the boiler's eBUS (electronic bus) communication network. The… Read more →
F.52 The F.52 code appears on Vaillant ecoTEC boilers when the control board detects a problem with the mass flow sensor… Read more →
F.53 The Vaillant F.53 fault code indicates a problem with the boiler's mass flow sensor — a component mounted just behind… Read more →
F.54 The F.54 fault code on a Vaillant boiler indicates that the appliance cannot detect or draw enough gas to establish a… Read more →
F.56 The Vaillant F.56 fault code is a lockout error that can carry slightly different meanings depending on which model you… Read more →
F.57 The F.57 code appears on Vaillant boilers when a fault is detected during comfort safety mode — essentially the… Read more →
F.60 The F.60 code appears when the boiler's PCB (Printed Circuit Board) has detected a problem communicating with or… Read more →
F.61 The F.61 code on a Vaillant boiler signals a gas valve control or communication fault. In plain terms, the boiler's… Read more →
F.62 The F.62 code is a combustion safety fault. It appears when your Vaillant boiler detects that the flame has switched… Read more →
F.63 The F.63 code on a Vaillant boiler signals an EEPROM error — a problem with the small but critical memory chip embedded… Read more →
F.64 The F.64 fault code on a Vaillant boiler signals that the control board has detected either a short circuit in one of… Read more →
F.65 The F.65 fault code indicates that your Vaillant boiler's main printed circuit board (PCB) has detected an unsafe rise… Read more →
F.67 The F.67 code appears on Vaillant boilers when the control board receives a flame signal that falls outside the… Read more →
F.68 The F.68 code indicates that your Vaillant boiler has detected an unstable or erratic flame signal. Rather than burning… Read more →
F.70 The F.70 code means your Vaillant boiler's main control board (PCB) does not have a valid Device-Specific Number (DSN)… Read more →
F.71 The F.71 code appears on Vaillant boilers when the PCB detects a problem with the heating flow NTC thermistor — the… Read more →
F.72 The F.72 code appears when your Vaillant boiler detects an unacceptable gap between the temperature readings from its… Read more →
F.73 The F.73 fault code indicates that the boiler's printed circuit board (PCB) is receiving no usable signal from the… Read more →
F.74 The F.74 fault code appears on Vaillant ecoTEC boilers when the water pressure sensor sends a signal to the PCB that… Read more →
F.75 No pressure change detected when the pump starts — typically a faulty pump or water pressure sensor. Read more →
F.76 The F.76 code appears on Vaillant ecoTEC Plus boilers when the thermal fuse mounted on the primary heat exchanger has… Read more →
F.77 The F.77 code appears on Vaillant boilers when the condensate removal system has encountered a problem serious enough… Read more →
F.78 The F.78 code on a Vaillant boiler indicates that the boiler has detected an interruption in the domestic hot water… Read more →
F.83 The F.83 code on a Vaillant boiler indicates that after the burner has ignited, the flow and return pipe sensors have… Read more →
F.84 The F.84 code appears on Vaillant boilers when the control board detects a persistent, unresolved temperature… Read more →
F.85 The F.85 code appears when the boiler's control board detects an implausible temperature relationship between the flow… Read more →
F.87 The F.87 code on a Vaillant boiler indicates a safety lockout triggered by incorrect flame detection — specifically,… Read more →
F.88 The F.88 code means your Vaillant boiler has detected an electrical fault associated with the gas valve. The boiler… Read more →
F.89 The F.89 code appears when the boiler loses a reliable signal from the heating flow NTC (Negative Temperature… Read more →
F.90 The F.90 code appears on Vaillant boilers when communication between the main PCB and either the display board or a… Read more →
F.91 The F.91 fault code on a Vaillant boiler has two distinct meanings depending on your model, so identifying your boiler… Read more →
F.92 The F.92 code on a Vaillant boiler signals a gas group configuration mismatch. In practical terms, the coding resistor… Read more →
F.93 The F.93 fault code on Vaillant boilers indicates that the combustion regulation system has detected the air-to-gas… Read more →