Johnson Starley Warmaflow F80E Fault codes & diagnostics

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

Regular Natural Gas 23.4 kW Discontinued

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33 High 3 Medium
Just want the most common Johnson Starley Warmaflow F80E faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 36 documented codes

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12

Your boiler has stopped working and locked itself for safety because it failed to light or stay lit correctly.

High DIY-safe £100-280

What to check first

  1. Check if your gas prepay meter has credit and that the gas supply is turned on.
  2. Press and hold the reset button for 5 seconds to see if the boiler restarts.
  3. If you have a condensate pipe leading outside, check that it is not frozen if the weather is very cold.

Parts commonly replaced

  • Ignition electrode
  • Flame sensing probe
  • Gas valve
Full explanation for 12
13

Your boiler has tried to light itself several times without success and has now locked itself out for safety.

High DIY-safe £120-350

What to check first

  1. Check that your gas prepayment meter has credit
  2. Ensure other gas appliances, like a cooker, are working to confirm gas supply
  3. Press the reset button on the boiler control panel once

Parts commonly replaced

  • Ignition electrode
  • Flame rectification probe
  • Gas valve

Related codes

Full explanation for 13
21

Your boiler's electronic control board is having trouble processing signals from its internal sensors, causing it to shut down for safety.

High Engineer only £180-350

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for 21
25

Your boiler's computer memory has encountered a software data error and it cannot process instructions correctly.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for 25
26

Your boiler is repeatedly struggling to keep the burner lit, causing it to shut down for safety.

High Engineer only £120-280

Parts commonly replaced

  • Flame sensing electrode
  • Ignition lead
  • Gas valve
  • PCB

Related codes

Full explanation for 26
30

Your boiler has stopped working because its internal thermometer has developed an electrical fault and can no longer monitor the water temperature accurately.

High Engineer only £90-160

Parts commonly replaced

  • Flow temperature sensor (NTC thermistor)
  • Connecting wiring harness

Related codes

Full explanation for 30
31

Your boiler has stopped working because it cannot accurately measure the temperature of the water being sent to your radiators.

High Engineer only £100-£180

Parts commonly replaced

  • Central heating flow NTC thermistor
  • Wiring harness
  • Control PCB

Related codes

Full explanation for 31
32

Your boiler has detected an electrical fault with the sensor that monitors your hot water temperature, which means it cannot safely heat water for your taps.

Medium Engineer only £90-160

Parts commonly replaced

  • Domestic Hot Water (DHW) Thermistor
  • Temperature Sensor Wiring Harness

Related codes

Full explanation for 32
34

Your boiler has detected that the electricity supply coming into your home is too weak for it to operate safely.

High Engineer only £90-180

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Voltage Regulator
Full explanation for 34
37

Your boiler has detected that there is not enough water pressure in the system to operate safely, causing it to shut down.

High DIY-safe £0-160

What to check first

  1. Locate the filling loop (usually a silver flexible hose) under or near the boiler.
  2. Slowly open the small valves on the filling loop until you hear water flowing.
  3. Watch the pressure gauge and close the valves once the needle reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop valves
  • Expansion vessel
  • Pressure sensor
Full explanation for 37
Showing 11–20 of 36
40

Your boiler has too much water in the system, which puts extra stress on the internal components.

Medium DIY-safe £0-120

What to check first

  1. Check that the filling loop valves are tightly closed
  2. Bleed water from a radiator using a bleed key to reduce pressure
  3. Monitor the pressure gauge to ensure it returns to between 1.0 and 1.5 bar
  4. Reset the boiler once the pressure is stabilised

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Pressure relief valve
Full explanation for 40
41

Your boiler has stopped working because it cannot detect any water pressure in the system.

High DIY-safe £100-240

What to check first

  1. Check the pressure gauge on the front of the boiler or under the casing.
  2. If the needle is below 1 bar, use the external filling loop valves to top up the water pressure to 1.5 bar.
  3. Reset the boiler to clear the fault code.

Parts commonly replaced

  • Water pressure sensor
  • Pressure switch
  • Expansion vessel

Related codes

Full explanation for 41
45

Your boiler has detected an electrical fault with the sensor that measures the temperature of the exhaust gases, causing it to shut down for safety.

High Engineer only £120-£220

Parts commonly replaced

  • Flue Gas Temperature Sensor (NTC)
  • Wiring Harness
  • Main Control Board

Related codes

Full explanation for 45
46

Your boiler has stopped working because it can no longer safely monitor the temperature of the exhaust gases leaving the system.

High Engineer only £120-210

Parts commonly replaced

  • Flue gas temperature sensor (thermistor)
  • Wiring harness connectors

Related codes

Full explanation for 46
47

Your boiler has stopped working because it cannot detect any information from the water pressure sensor, likely due to a wiring fault or a broken internal part.

High Engineer only £140-220

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness
  • Main control board

Related codes

Full explanation for 47
E01

Your boiler has failed to light after several attempts and has locked itself for safety.

High DIY-safe £90-280

What to check first

  1. Check that your gas pre-payment meter (if you have one) has credit
  2. Ensure other gas appliances in the home, like a hob, are working correctly
  3. Press and hold the reset button for five seconds to restart the ignition sequence

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Probe
  • Gas Valve

Related codes

Full explanation for E01
E02

Your boiler thinks it sees a flame even though it isn't supposed to be running, causing it to shut down for safety.

High DIY-safe £100-280

What to check first

  1. Locate the reset button on the control panel
  2. Press and hold the reset button for 2 to 5 seconds
  3. Wait for the boiler to restart and check if the error clears

Parts commonly replaced

  • Flame sensing electrode
  • Printed Circuit Board (PCB)
  • Gas valve

Related codes

Full explanation for E02
E03

Your boiler has got too hot and has shut itself down as a safety precaution to prevent damage.

High DIY-safe £90-250

What to check first

  1. Check that all radiator valves are fully open to allow water to flow.
  2. Ensure there is enough water pressure in the system by checking the pressure gauge (should be around 1 to 1.5 bar).
  3. Once the boiler has cooled down, press the reset button on the control panel.

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Thermistor (NTC Sensor)

Related codes

Full explanation for E03
E05

Your boiler has detected an issue with the fan that safely removes exhaust gases, causing the system to shut down for safety.

High Engineer only £180-£350

Parts commonly replaced

  • Fan Assembly
  • Fan Pressure Switch
  • PCB
Full explanation for E05
E08

Your boiler is failing to detect the flame it needs to stay lit, which means the system is shutting down for safety.

High Engineer only £120-350

Parts commonly replaced

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

Related codes

Full explanation for E08
Showing 21–30 of 36
E09

Your boiler has detected a communication problem with the internal gas valve, which means it cannot safely control the fuel flow and has shut down.

High Engineer only £180-350

Parts commonly replaced

  • Gas Valve
  • Wiring Harness
  • Main Control Board

Related codes

Full explanation for E09
E12

Your boiler's internal memory chip has developed a software error or a communication failure, causing the system to shut down for safety.

High Engineer only £280-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Control Module

Related codes

Full explanation for E12
E15

Your boiler has shut down because its internal temperature sensors are giving conflicting readings and can no longer monitor the heat safely.

High Engineer only £120-£220

Parts commonly replaced

  • Flow NTC sensor
  • Return NTC sensor
  • Main control board

Related codes

Full explanation for E15
E16, E17, E18

Your boiler has detected that a temperature sensor is stuck or giving an incorrect reading, which has caused the system to shut down for safety.

High Engineer only £120-£220

Parts commonly replaced

  • Flow NTC Temperature Sensor
  • Return NTC Temperature Sensor
  • Control PCB

Related codes

Full explanation for E16, E17, E18
E21

Your boiler's internal computer has encountered a memory or signal processing error and has shut down as a safety precaution.

High Engineer only £180-450

Parts commonly replaced

  • Main Control PCB
  • Wiring Loom

Related codes

Full explanation for E21
E33

Your boiler's temperature sensor responsible for monitoring water as it returns to the unit has developed a fault, preventing the system from heating correctly.

High Engineer only £120-190

Parts commonly replaced

  • Return thermistor (NTC sensor)
  • Wiring harness
  • PCB

Related codes

Full explanation for E33
E34

Your boiler has detected that the electricity supply coming into the unit is too low to operate safely, causing it to shut down to protect its components.

High DIY-safe £100-280

What to check first

  1. Check if there is a power cut or brownout in your local area.
  2. Ensure the boiler is plugged into a dedicated socket or fused spur and not an extension lead.
  3. Reset the boiler once you are certain the mains power supply is stable.

Parts commonly replaced

  • External Power Supply Cable
  • PCB (Printed Circuit Board)
  • Voltage Stabiliser

Related codes

Full explanation for E34
E35

Your boiler's internal thermometer that monitors water temperature has stopped working correctly, preventing the system from heating up.

High Engineer only £90-160

Parts commonly replaced

  • Flow thermistor (NTC sensor)
  • Thermistor wiring harness

Related codes

Full explanation for E35
F07

Your boiler has detected an issue with the sensor that monitors the safety of the exhaust gases, and it has shut down to prevent potential overheating.

High Engineer only £120-£240

Parts commonly replaced

  • Exhaust thermistor
  • Flue gas sensor
  • Wiring harness
Full explanation for F07
F13

Your boiler has stopped running because it has locked itself out after too many unsuccessful reset attempts from a remote control or thermostat.

High DIY-safe £0-120

What to check first

  1. Locate the main power switch for your boiler (usually a fused spur near the unit).
  2. Turn the power OFF for 30 seconds, then turn it back ON.
  3. Press the physical RESET button on the boiler control panel itself to clear the memory.

Parts commonly replaced

  • Main PCB (if software is stuck)
  • Remote thermostat transmitter
Full explanation for F13
Showing 31–36 of 36
F37

Your boiler has detected that the water pressure in the system has dropped too low to operate safely.

High DIY-safe £0-160

What to check first

  1. Locate the filling loop, which is usually a flexible silver hose under the boiler.
  2. Slowly open the small valves on the filling loop until you hear water flowing.
  3. Watch the pressure gauge and close the valves once the needle reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop valves
  • Expansion vessel
  • Pressure sensor

Related codes

Full explanation for F37
F40

Your boiler has too much water inside it, which is causing it to shut down for safety.

High DIY-safe £80-160

What to check first

  1. Check that the filling loop valves are fully closed
  2. Bleed a radiator from a bottom-floor valve to release excess pressure
  3. Monitor the pressure gauge to ensure it returns to between 1.0 and 1.5 bar
  4. Press the reset button once the pressure is back within the normal range

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Pressure relief valve
Full explanation for F40
F47

Your boiler has stopped working because it cannot detect the sensor that monitors water pressure within the system.

High Engineer only £100-£220

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness
  • Main PCB
Full explanation for F47
F52

Your boiler is having trouble measuring the temperature of your hot water, which means you may have inconsistent or no hot water at your taps.

Medium Engineer only £100-£190

Parts commonly replaced

  • DHW Temperature Sensor (NTC Thermistor)
  • Wiring harness connecting the sensor

Related codes

Full explanation for F52
F53

Your boiler has shut down because a sensor has detected that the exhaust gases are getting too hot, which is a safety measure to prevent damage.

High Engineer only £120-£250

Parts commonly replaced

  • Flue Temperature Sensor (NTC)
  • Main Heat Exchanger
  • Fan Assembly

Related codes

Full explanation for F53
Fault Image

Your boiler has detected that the burner is not working correctly, causing the system to lock out for safety.

High Engineer only £120-350

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

Full explanation for Fault Image