Biasi Basica Combi Fault codes & diagnostics

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

Combi Natural GasLPG 24-28 kW 2019-present
GC Numbers 47-583-4947-583-5047-583-51
Download the Biasi Basica Combi manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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Severity at a glance

Each cell = one fault code. Hover to identify.
1 Emergency 24 High 2 Medium
Just want the most common Biasi Basica Combi faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 27 documented codes

Tap any card for details

E01

Your boiler has failed to light the gas or cannot detect the flame, meaning you have no heating or hot water until it is reset or repaired.

High DIY-safe £100-280

What to check first

  1. Check if your gas supply is active and other gas appliances are working
  2. Check if you have credit on your prepayment gas meter
  3. Press and hold the Reset button for 5 seconds to attempt a restart

Parts commonly replaced

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

Related codes

Full explanation for E01
E02

Your boiler has shut itself down because it has become too hot to operate safely.

High DIY-safe £90-280

What to check first

  1. Check that all radiator valves are fully open to allow water flow.
  2. Verify that the boiler pressure is between 1.0 and 1.5 bar on the gauge.
  3. Press and hold the 'R' reset button for 5 seconds to see if the fault clears.

Parts commonly replaced

  • Safety Thermostat (Overheat Stat)
  • Circulating Pump
  • Heat Exchanger (de-scaling)

Related codes

Full explanation for E02
E03

Your boiler has detected that it is getting too hot or that there is a problem safely venting exhaust gases, causing the system to shut down for safety.

High Engineer only £120-£250

Parts commonly replaced

  • Flue thermostat
  • Thermal fuse
  • Fan
  • Main PCB

Related codes

Full explanation for E03
E04

Your boiler has detected that water isn't moving through the system quickly enough, causing it to overheat and shut down for safety.

High DIY-safe £100-£350

What to check first

  1. Check that the boiler pressure is between 1.0 and 1.5 bar on the gauge
  2. Ensure all radiator valves and the boiler's isolation valves are fully open
  3. Bleed all radiators to remove trapped air that could be blocking flow

Parts commonly replaced

  • Circulation pump
  • Primary heat exchanger
  • Main PCB

Related codes

Full explanation for E04
E05

Your boiler has stopped working because the fan that removes waste gases cannot spin at the correct speed or has failed completely.

High Engineer only £180-350

Parts commonly replaced

  • Fan motor
  • Main circuit board (PCB)
  • Venturi tube

Related codes

Full explanation for E05
E06

Your boiler's internal temperature sensor for the radiators has stopped working correctly, which means the system cannot safely monitor how hot the water is getting.

High Engineer only £90-160

Parts commonly replaced

  • CH Temperature Sensor (NTC Probe)
  • Wiring Harness

Related codes

Full explanation for E06
E07

Your boiler's hot water sensor has failed or is disconnected, meaning your taps may not get hot or the temperature will be inconsistent.

Medium Engineer only £90-160

Parts commonly replaced

  • Domestic Hot Water (DHW) NTC Sensor
  • Sensor wiring harness

Related codes

Full explanation for E07
E08

Your boiler has detected an issue with the sensor that monitors the temperature of the exhaust gases, causing the system to shut down for safety.

High Engineer only £120-190

Parts commonly replaced

  • Flue NTC thermistor
  • Wiring harness
  • Main circuit board (PCB)

Related codes

Full explanation for E08
E09

Your boiler has detected a problem with the sensor that monitors the temperature of the exhaust fumes, causing the system to shut down for safety.

High Engineer only £120-190

Parts commonly replaced

  • Flue Gas NTC Sensor
  • Sensor Wiring Harness

Related codes

Full explanation for E09
E10

Your boiler has shut down because it detected that the exhaust gases have become dangerously hot, causing a safety fuse to blow.

High Engineer only £120-£250

Parts commonly replaced

  • Flue gas probe
  • Thermal fuse
  • Main heat exchanger

Related codes

Full explanation for E10
Showing 11–20 of 27
E11

Your boiler thinks a flame is present before it has even started the ignition process, which is a safety conflict that prevents it from firing up.

High Engineer only £120-300

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Main PCB

Related codes

Full explanation for E11
E12

Your boiler has detected a problem with the internal sensor that monitors the temperature of the water returning to the unit, which is preventing it from running safely.

High Engineer only £90-160

Parts commonly replaced

  • Return NTC thermistor
  • Connecting wiring harness

Related codes

Full explanation for E12
E13

Your boiler has detected that there is too much water pressure in the central heating system.

High DIY-safe £80-160

What to check first

  1. Check that the internal or external filling loop valves are tightly closed.
  2. Bleed water from a radiator using a radiator key to lower the pressure.
  3. Monitor the pressure gauge on the boiler until it sits between 1 and 1.5 bar.

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Pressure relief valve (PRV)

Related codes

Full explanation for E13
E14

Your boiler has stopped working because water is not moving through the system quickly enough to prevent it from overheating.

High DIY-safe £150-£350

What to check first

  1. Check that the boiler pressure is between 1 and 1.5 bar on the gauge
  2. Ensure all radiator valves and isolation valves under the boiler are fully open
  3. Try resetting the boiler to see if the error clears

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger
  • Pump Motor Head

Related codes

Full explanation for E14
E22

Your boiler is getting too hot and has shut down as a safety precaution to prevent overheating.

High DIY-safe £120-£350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure is between 1.0 and 1.5 bar
  3. Restart the boiler using the reset button

Parts commonly replaced

  • Circulation pump
  • Central heating thermistor (NTC sensor)
  • Main heat exchanger (descaling)

Related codes

Full explanation for E22
E25

Your boiler has detected that the internal water temperature is dangerously low and has entered a protective mode to prevent the pipes from freezing.

High DIY-safe £0-120

What to check first

  1. Check that your electricity supply to the boiler is switched on.
  2. Ensure your gas supply is active (check other gas appliances).
  3. Open any radiator valves fully to allow water circulation.
  4. If your condensate pipe is frozen outside, gently pour warm (not boiling) water over it to thaw it.

Parts commonly replaced

  • Temperature Sensor (NTC)
  • Circulation Pump

Related codes

Full explanation for E25
E26

Your boiler has detected a problem with how it controls the gas supply, meaning it cannot safely ignite or maintain a flame and has locked out for your protection.

High Engineer only £180-350

Parts commonly replaced

  • Gas Valve
  • Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for E26
E28

Your boiler's hot water sensor has malfunctioned or developed a wiring fault, meaning the system can no longer monitor the temperature of your stored water.

Medium Engineer only £90-160

Parts commonly replaced

  • DHW Tank NTC Sensor
  • Sensor Wiring Harness

Related codes

Full explanation for E28
E50

Your boiler is having trouble communicating with your smart thermostat or external heating controller.

High DIY-safe £80-180

What to check first

  1. Check that your wall-mounted thermostat is turned on and has working batteries.
  2. Ensure the thermostat's receiver unit (usually near the boiler) has power.
  3. Reset the boiler by turning the selector switch to 'R' for five seconds and then back to 'ON'.

Parts commonly replaced

  • OpenTherm interface cable
  • External thermostat/programmer
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E50
E52

Your boiler has been locked for safety because too many attempts were made to reset it remotely without a physical inspection.

High Engineer only £80-200

Parts commonly replaced

  • Main PCB
  • External Control Interface

Related codes

Full explanation for E52
Showing 21–27 of 27
E54

Your boiler has tried to top itself up with water automatically but the pressure is still too low for it to start running.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (the flexible silver hose) underneath the boiler
  2. Open the filling valve(s) slowly until you hear water entering
  3. Watch the pressure gauge and close the valves when it reaches 1.5 bar
  4. Press the Reset button on the boiler control panel

Parts commonly replaced

  • Filling loop
  • Pressure sensor
  • Pressure gauge

Related codes

Full explanation for E54
E58

Your boiler has been filled with too much water, causing the system pressure to rise above the safe operating limit.

Emergency DIY-safe £0-120

What to check first

  1. Locate a radiator bleed valve and use a radiator key to carefully release a small amount of water into a container.
  2. Monitor the pressure gauge on the front of the boiler until it falls back into the green zone (typically 1.0 to 1.5 bar).
  3. Ensure the blue filling loops/taps underneath the boiler are fully closed and tightened.
  4. Reset the boiler to clear the fault code.

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Pressure sensor

Related codes

Full explanation for E58
Fault on gas supply

Your boiler has stopped working because it cannot detect a steady flow of gas, which has caused it to shut down for safety.

High DIY-safe £100-£350

What to check first

  1. Check if other gas appliances in your home, like a hob, are working to confirm your gas supply is active.
  2. If you have a prepaid meter, ensure you have sufficient credit available.
  3. Try resetting the boiler by turning the dial to the 'R' position for a few seconds.

Parts commonly replaced

  • Gas Valve
  • Ignition Electrode
  • Spark Generator
Full explanation for Fault on gas supply
Faulty condensate drainage

Your boiler has stopped working because the pipe that carries away excess liquid is blocked or frozen, causing water to back up into the unit.

High DIY-safe £80-140

What to check first

  1. Locate the plastic condensate pipe heading outside your property.
  2. Check if the end of the pipe is frozen and pour warm (not boiling) water over it to melt the ice.
  3. Restart the boiler once the blockage is clear and the liquid has drained.

Parts commonly replaced

  • Condensate trap
  • External pipe insulation
  • Condensate pump
Full explanation for Faulty condensate drainage
Faulty flame detection

Your boiler is struggling to confirm that the gas has successfully lit, so it has shut down as a safety precaution.

High Engineer only £90-180

Parts commonly replaced

  • Flame detection electrode
  • Ignition lead
  • Printed Circuit Board (PCB)
Full explanation for Faulty flame detection
Faulty gas valve

Your boiler is unable to light the gas burner, meaning you will not have any heating or hot water until it is repaired.

High Engineer only £220-380

Parts commonly replaced

  • Gas valve
  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for Faulty gas valve
Faulty ignition

Your boiler is failing to light the gas, which means your heating and hot water will not work until the ignition system is checked.

High Engineer only £120-£250

Parts commonly replaced

  • Ignition electrodes
  • Ignition lead
  • Spark generator
  • Printed Circuit Board (PCB)
Full explanation for Faulty ignition
Status & diagnostic codes

3 operating states & engineer diagnostics

Not faults — these are normal operating states. Tap to expand.

OFF Status Your boiler is currently set to standby mode and will not provide heating or hot water until it is switched back on. P00 Diagnostic Your boiler has entered its internal settings menu and is waiting for a configuration code to be entered. P06 Diagnostic Your boiler is currently running in a special engineer-only testing mode used to check flue gases, meaning it is not in its normal operating state.
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