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boiler service, boiler repair, emergency repair
Vaillant Home System 18 Boiler Fault Codes
| Code | Meaning | Possible Cause |
| F22 | Safety switch-off: Low water pressure in the boiler | No or insufficient water in the product, water pressure sensor defective, cable to the pump or to the water pressure sensor loose/not connected/defective |
| F23 | Safety switch-off: Temperature difference too great (NTC1/NTC2) | Pump blocked, insufficient pump output, air in product, flow and return NTC sensors connected the wrong way round |
| F24 | Safety switch-off: Temperature rise too fast | Pump blocked, reduced pump output, air in product, system pressure too low, return flow prevention blocked/incorrectly installed |
| F25 | Safety switch-off: Flue gas temperature too high | Break in connection for optional flue gas safety temperature limiter (safety cut-out), break in cable harness |
| F27 | Safety switch-off: Fault in flame detection | Moisture on the electronics, electronics (flame monitor) defective, gas solenoid valve leaking |
| F28 | Fault: Ignition unsuccessful when starting up | Gas meter defective or gas pressure monitor has triggered, air in gas, gas flow pressure too low, thermal isolator device (TAE) has triggered, incorrect gas restrictor, incorrect spare gas valve, fault on the gas valve, multiple plug on PCB incorrectly plugged in, break in cable harness, ignition system (ignition transformer, ignition cable, ignition plug, ignition electrode) defective, ionisation current interrupted (cable, electrode), incorrect earthing of product, electronics defective |
| F29 | Fault: Flame loss | Gas supply temporarily stopped, flue gas recirculation, incorrect earthing of product, ignition transformer has spark failure |
| F32 | Fan frost protection function active: Fan speed outside the tolerance values | Plug on fan not correctly plugged in, multiple plug on PCB not correctly plugged in, break in cable harness, fan blocked, Hall sensor defective, electronics defective |
| F33 | Fan frost protection function active: Air pressure switch fault | Pressure monitor has not switched or has switched at a fan speed value that is too high (insufficient air supply) Pressure monitor plug not correctly plugged in, pressure monitor defective, line removed from between the pressure monitor and silencer, air/flue pipe blocked and silencer not installed properly |
| F49 | eBUS fault: Voltage too low | Short circuit on eBUS, eBUS overload or two power supplies with different polarities on the eBUS |
| F61 | Fault: Gas valve control system | Short circuit/short to earth in cable harness for the gas valve, gas valve defective (coils shorted to earth), electronics defective |
| F62 | Fault: Gas valve switch-off control | Delayed switch-off of gas valve, delayed extinguishing of flame signal, gas valve leaking, electronics defective |
| F63 | Fault: EEPROM | Electronics defective |
| F64 | Fault: Electronics/sensor/analogue-to-digital converter | Flow or return NTC short circuited, electronics defective |
| F65 | Fault: Electronics temperature too high | Electronics overheating due to external influences, electronics defective |
| F67 | Value sent back by ASIC is incorrect (flame signal) | Implausible flame signal, electronics defective |
| F68 | Fault: Unstable flame (analogue input) | Air in gas, gas flow pressure too low, incorrect air ratio, incorrect gas restrictor, ionisation flow interruption (cable, electrode) |
| F70 | Invalid product code (DSN) | Replace the screen and PCB at the same time without reconfiguring the product's Device Specific Number |
| F71 | Fault: Flow/return temperature sensor | Flow temperature sensor specifies a constant value: Flow temperature sensor incorrectly attached to the flow pipe, flow temperature sensor defective |
| F72 | Fault: Deviation in the water pressure sensor/return temperature sensor | Flow/return NTC sensor temperature difference too great → flow and/or return temperature sensor defective |
| F73 | Fault: Water pressure sensor not connected or has short-circuited | Interruption/short circuit of water pressure sensor, interruption/short to earth in supply line to water pressure sensor or water pressure sensor defective |
| F74 | Fault: Electrical problem in the water pressure sensor | Line to water pressure sensor has a short circuit to 5 V/24 V or internal fault in the water pressure sensor |
| F75 | Fault: Pressure sensor | Pressure sensor or pump defective or low water pressure |
| F77 | Fault: Condensate or smoke | No response, flue non-return flap defective |
| F78 | Interruption to DHW outlet sensor at external controller | Link box connected, but hot water NTC not bridged |
| F83 | Fault: Burner temperature sensor |
Burner temperature sensor is defective When the burner starts, the temperature change recorded by the flow or return temperature sensor is non-existent or too small: Insufficient water in the product, flow or return temperature sensor incorrectly attached to the pipe |
| F84 | Fault: Flow/return temperature sensor |
Values not consistent, difference < -6 K Flow and return temperature sensors signalling implausible values: Flow and return temperature sensors have been inverted, flow and return temperature sensors have not been correctly installed |
| F85 | Fault: Temperature sensor | The flow and/or return temperature sensors have been installed on the same pipe/incorrect pipe Temperature sensor not connected or is connected incorrectly |
| F86 | Fault: Underfloor heating contact | Underfloor heating contact open, sensor disconnected or defective |
| F87 | Fault: Ignition electrode | Ignition electrode not connected or not connected properly, short circuit in the cable harness |
| F88 | Fault: Gas valve | Gas valve not connected or it is connected incorrectly, short circuit in the cable harness |
| F89 | Fault: Pump | Pump not connected or it is connected incorrectly, incorrect pump connected, short circuit in the cable harness |