Vaillant ecoFIT pure 612 Fault codes & diagnostics

40 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

System Gas 2016-present
GC Number 41-694-03
Download the Vaillant ecoFIT pure 612 manualThe official installation and service manual (PDF), the document these fault codes were read from. PDF

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Severity at a glance

Each cell = one fault code. Hover to identify.
5 Emergency 31 High 4 Medium

Which version do you have?

The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.

GC number Appliance (register name) Produced
41-694-03 ecoFIT pure 612 VU 126/6-3 (H-GB) 2016–present

Appliance names and production years are taken from the UK Product Characteristics Database (the SAP/SEDBUK register). Where a GC number is also printed in this model's own manufacturer manual, both sources were checked to agree.

All 40 documented codes

Tap any card for details

F.00

Your boiler has temporarily stopped working because it cannot accurately measure the temperature of the water leaving the system.

High Engineer only £120-220

Parts commonly replaced

  • Flow temperature sensor
  • Wiring harness

Related codes

F.01

Your boiler has temporarily stopped working because it cannot accurately measure the temperature of the water returning from your radiators.

Medium Engineer only £90-180

Parts commonly replaced

  • Return temperature sensor
  • Wiring harness

Related codes

F.10

Your boiler has temporarily stopped working because it has detected an electrical fault with one of its internal temperature sensors.

High Engineer only £90-180

Parts commonly replaced

  • Flow temperature sensor
  • Wiring harness

Related codes

F.11

Your boiler has temporarily stopped working because it has detected an electrical fault with one of its internal temperature sensors.

High Engineer only £90-180

Parts commonly replaced

  • Return temperature sensor
  • Wiring harness

Related codes

F.12

Your boiler is struggling to detect the temperature of your hot water due to a wiring issue or a faulty sensor, so it has stopped heating to prevent potential damage.

High Engineer only £120-220

Parts commonly replaced

  • Cylinder temperature sensor
  • Wiring harness

Related codes

F.13

Your boiler is having trouble 'reading' the temperature of your hot water supply because a wire or sensor has stopped communicating correctly.

Medium Engineer only £120-220

Parts commonly replaced

  • NTC sensor
  • Wiring harness
F.20

Your boiler has detected that it is running much hotter than it should be and has automatically switched itself off to prevent permanent damage.

High Engineer only £150-350

Parts commonly replaced

  • NTC Temperature Sensor
  • Pump
  • Primary Heat Exchanger
  • PCB

Related codes

F.22

Your boiler has stopped working because the amount of water circulating inside the heating system has dropped too low.

High DIY-safe £80-150

What to check first

  1. Locate the filling loop (a flexible metal hose) underneath your boiler.
  2. Open the valves on the filling loop to allow cold mains water into the system.
  3. Watch the pressure gauge on the front of the boiler until the needle reaches between 1.0 and 1.5 bar.
  4. Close both valves tightly and remove the filling loop if required by your specific model.

Parts commonly replaced

  • Pressure relief valve
  • Expansion vessel
  • Pressure sensor

Related codes

F.23

Your boiler has detected that the water temperature is rising or falling much faster than expected in different parts of the system, so it has shut itself down to prevent damage.

High Engineer only £150-300

Parts commonly replaced

  • Central heating pump
  • NTC temperature sensors
  • Heat exchanger

Related codes

F.24

Your boiler has detected that the water inside it is heating up much faster than it safely should, causing it to shut down to prevent damage.

High Engineer only £150-350

Parts commonly replaced

  • Central heating pump
  • System filter
  • Heat exchanger
  • Flow sensor

Related codes

Showing 11–20 of 40
F.25

Your boiler has detected that the gases it is producing are too hot to be safe, so it has automatically shut down to prevent damage.

Emergency Engineer only £150-350

Parts commonly replaced

  • Flue gas temperature sensor
  • NTC thermistor
  • Primary heat exchanger

Related codes

F.27

Your boiler has failed to confirm that the burner is safely lit, so it has automatically shut itself down to prevent a gas leak.

Emergency Engineer only £150-300

Parts commonly replaced

  • Flame rectification electrode
  • Ignition lead
  • Printed Circuit Board (PCB)

Related codes

F.28

Your boiler is failing to light the flame needed to produce heat or hot water.

High Engineer only £150-350

Parts commonly replaced

  • Ignition lead
  • Ignition electrode
  • Gas valve
  • Printed Circuit Board

Related codes

F.29

Your boiler is failing to stay lit, which means it has safely shut itself down because it cannot consistently produce or hold a flame.

High Engineer only £150-350

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed Circuit Board (PCB)
  • Flame rectification probe

Related codes

F.32

Your boiler has detected that the fan, which pushes waste gases outside, isn't spinning at the correct speed to ensure safe operation.

High Engineer only £150-350

Parts commonly replaced

  • Fan unit
  • Printed Circuit Board (PCB)
  • Wiring harness
F.49

Your boiler's communication system is experiencing a power supply issue, causing it to lose its ability to talk to your thermostat or internal components.

High Engineer only £120-250

Parts commonly replaced

  • eBUS PCB
  • Wiring harness
  • External thermostat/controller

Related codes

F.61

Your boiler is unable to properly manage the flow of gas required for heating and hot water, so it has safely shut itself down to prevent a hazard.

Emergency Engineer only £150-350

Parts commonly replaced

  • Gas valve
  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

F.62

Your boiler has detected an issue with the internal safety mechanism that controls the gas flow, so it has safely shut itself down to prevent operation.

High Engineer only £250-450

Parts commonly replaced

  • Gas valve
  • Main printed circuit board (PCB)

Related codes

F.63

Your boiler's internal computer has encountered a memory error and cannot read the essential configuration data required to operate safely.

High Engineer only £300-600

Parts commonly replaced

  • Main PCB
  • Display PCB

Related codes

F.64

Your boiler's main computer control panel is failing to process signals from its sensors, meaning it cannot safely operate the system.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB
  • Wiring harness

Related codes

Showing 21–30 of 40
F.65

Your boiler has detected that its internal control brain is overheating and has shut itself down to prevent damage.

High Engineer only £150-350

Parts commonly replaced

  • Main PCB
  • Wiring harness

Related codes

F.67

Your boiler's computer is struggling to safely detect or manage the flame, so it has shut itself down to prevent any unsafe operation.

High Engineer only £200-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Flame rectification electrode

Related codes

F.68

Your boiler is struggling to keep a steady flame, causing it to shut down for safety reasons.

High Engineer only £150-300

Parts commonly replaced

  • Gas valve
  • PCB board
  • Flame sensor

Related codes

F.70

Your boiler has lost its unique digital identity, meaning the internal computer no longer knows how to correctly control your specific heating system.

High Engineer only £120-250

Parts commonly replaced

  • User Interface PCB
  • Main PCB

Related codes

F.71

Your boiler is struggling to accurately measure the temperature of the water flowing through the system, so it has safely shut itself down to prevent overheating.

High Engineer only £150-250

Parts commonly replaced

  • Flow NTC sensor
  • Return NTC sensor
  • Wiring harness

Related codes

F.72

Your boiler is having trouble reading the water pressure or temperature accurately, which has caused it to switch itself off for safety.

High Engineer only £150-£300

Parts commonly replaced

  • Water pressure sensor
  • NTC return temperature sensor
  • Main printed circuit board

Related codes

F.73

Your boiler's internal water pressure gauge is failing to signal correctly, meaning the system cannot confirm it has enough water to operate safely.

High Engineer only £150-250

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness

Related codes

F.74

Your boiler is struggling to accurately measure its own internal water pressure, so it has stopped working to prevent potential damage to the system.

High Engineer only £150-250

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness

Related codes

F.75

Your boiler is struggling to detect the water pressure inside the system, which prevents it from firing up safely.

High Engineer only £150-250

Parts commonly replaced

  • Pressure sensor
  • Heating pump

Related codes

F.76

Your boiler has detected an internal safety sensor fault within the main heating unit and has safely locked itself out to prevent any risk.

Emergency Engineer only £150-300

Parts commonly replaced

  • Primary heat exchanger safety thermal fuse
  • Overheat safety thermostat
  • Wiring harness

Related codes

Showing 31–40 of 40
F.77

Your boiler has detected an issue with how it clears water or exhaust gases, meaning it has switched itself off to stay safe.

High Engineer only £150-300

Parts commonly replaced

  • Condensate trap
  • Condensate pump
  • Flue sensor

Related codes

F.78

Your boiler has lost communication with a sensor that monitors your hot water, which means it has stopped heating your water to prevent potential system damage.

High Engineer only £150-250

Parts commonly replaced

  • Domestic hot water sensor
  • Wiring harness

Related codes

F.83

Your boiler has detected that there is not enough water circulating inside the system to carry the heat away safely.

High Engineer only £150-300

Parts commonly replaced

  • NTC sensor
  • Pressure sensor
  • Heating pump

Related codes

F.84

Your boiler is struggling to compare the temperature of the water leaving and returning, meaning it cannot safely control its heating output.

High Engineer only £150-250

Parts commonly replaced

  • NTC temperature sensor
  • Wiring harness
  • Printed Circuit Board

Related codes

F.85

Your boiler is struggling to read its own internal water temperature correctly, so it has stopped working to prevent potential damage.

High Engineer only £120-220

Parts commonly replaced

  • Flow temperature sensor
  • Wiring harness
  • PCB

Related codes

F.86

Your boiler has detected that the external safety switch connected to an underfloor heating system is signaling a fault or that the connection is open.

Medium Engineer only £120-250

Parts commonly replaced

  • Underfloor heating limit switch
  • Wiring harness
  • PCB

Related codes

F.87

Your boiler is having trouble detecting or maintaining the flame safely, so it has shut down to prevent any issues.

High Engineer only £120-250

Parts commonly replaced

  • Ignition lead
  • Spark electrode
  • PCB

Related codes

F.88

Your boiler has detected an issue with the assembly that controls the gas supply, meaning it cannot ignite safely to provide heating or hot water.

Emergency Engineer only £200-350

Parts commonly replaced

  • Gas valve
  • Gas valve wiring harness

Related codes

F.89

Your boiler is struggling because the internal pump that moves hot water through your home's radiators and taps has stopped working correctly.

High Engineer only £250-450

Parts commonly replaced

  • Central heating pump
  • Wiring harness

Related codes

F.91

Your boiler is having trouble communicating with the temperature sensor in your hot water cylinder, which means it may not be able to heat your taps or shower correctly.

Medium Engineer only £120-200

Parts commonly replaced

  • Cylinder temperature sensor (NTC)
  • Wiring harness

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