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Vaillant Boiler Fault Codes and Errors

Coming home to find your Vaillant boiler is in lockout and is flashing error codes can be quite frustrating. This is simply because if the issue is serious, there won’t be any domestic hot water supply or central heating until the issue is resolved and the boiler is up and running again.

But how can you resolve the error codes displayed on your boiler’s display panel? Well, you first have to decode the meaning of these error codes before deciding on the appropriate course of action. And we are here to help you do that.

But since the entire Vaillant boiler fault codes are extensive and vary from one boiler model to another, we won’t be covering all the possible fault codes. So instead, this guide focuses on explaining the meaning of some of the most common Vaillant boiler fault codes.

Common Vaillant Boiler Fault Codes and Errors



Description Possible Cause
F.0/F.00 There is an interruption in the flow sensor The flow temperature sensor is defective or not connected.
F.01 There is an interruption in the return sensor. The return temperature sensor is defective or is not connected.
F.10 Faulty flow sensor The flow NTC has short-circuited or is defective
F.11 Faulty return sensor The return NTC has short-circuited or is defective
F.20 Safety switch-off activated by the temperature limiter The temperature at the flow/return temperature sensor has exceeded tolerable limits
F.22 Safety switch-off due to low water pressure in the boiler There is no/insufficient water in the boiler system, or the water pressure is too low
F.23 Safety switch-off due to large temperature spread The temperature spread is too great, or the water circulation in the system is too low
F.24 The temperature rise in the boiler is too rapid, resulting in a safety switch-off Faulty pump, presence of air in the system, or system pressure is too low
F.25 Excessive flue gas temperature prompting a safety switch-off Faulty flue gas safety temperature limiter
F.26 Faulty gas valve The gas valve assembly stepper motor is defective or not properly connected
F.27 Safety switch-off during flame simulation The monitoring electrode detected an incorrect flame
F.28 Start-up failure caused by a failed ignition Unsuccessful ignition due to faulty gas pressure monitor or a thermal cut-out
F.29 Operating failure caused by a failed ignition Temporary gas supply interruption or low gas pressure
F.32 Fan error The fan is either defective or is not connected
F.49 eBUS error Low voltage supply to the eBUS or a possible short-circuit
F.61 Gas valve regulation error The gas valve is defective, not connected, or is connected incorrectly
F.62 Faulty gas valve due to a switch-off delay Delayed gas valve shut down, defective electronics, or delayed extinguishing of flame signal
F.63 EPROM fault Defective boiler electronics
F.64 Electronics or NTC error Defective boiler electronics, probably the supply or return NTC is short-circuited
F.65 Overheating boiler electronics Defective electronics or overheating is caused by external influences
F.67 Electronics flame signal error Defective boiler electronics or implausible flame signal
F.68 Unstable flame signal Faulty flame monitor, presence of air in gas, wrong air ratio, blocked condensate pipe, incorrect gas restrictor, low gas flow pressure
F.70 Invalid Device Specific Number (DSN) The PCB and the display units were replaced at the same time, and the DSN was not set correctly. A faulty/ missing coding resistor can also cause it
F.71 NTC flow error The flow temperature sensor is defective or incorrectly placed, or stuck at one value
F.72 Faulty NTC flow/return sensor The flow/return sensor temperature difference is too big, or the sensor is damaged
F.73 The water pressure sensor signal reads a value outside the acceptable range, i.e., it is too low The water pressure sensor is defective or is short-circuited
F.74 The water pressure sensor signal reads a value outside the acceptable range, i.e., it is too low The cable to the water pressure sensor may be short-circuited, or the sensor may be faulty
F.75 No pressure change is detected in the boiler even after the pump starts Defective water pressure sensor/ pump  or low water pressure in the system, or presence of air in the system
F.76 Overheating protection feature activated on the primary heat exchanger Faulty wiring in the primary heat exchanger
F.77 Faulty flue non-return flap or condensate pump The flue non return flap or condensate pump is defective
F.78 The DHW outlet sensor has been interrupted at the external controller The hot water NTC is defective or not connected
F.83 Faulty flow and/ return temperature  sensor Incorrect position of the flow or return temperature sensor
F.84 The flow/ return sensor is returning implausible values The flow/return sensors are faulty or have been incorrectly fitted
F.85 The flow and the return temperature sensors have been incorrectly fitted The two sensors have been fitted on the same pipe
F.92 Coding resistor issue or incorrect gas type There is a mismatch between the coding on the PCB resistor and the gas family
F.93 Faulty gas route or wrong gas group The gas family check was prematurely terminated, or the combustion quality of the gas is outside the permitted range
Communication fault There is no communication between the display unit and the PCB unit  


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