Atag E Range Fault codes & diagnostics

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

Combi Natural Gas 24-38 kW 2013-2018 Discontinued

Replaced by: iC Series

This boiler uses LED flash patterns

Count the flashes in one repeating group before the pause. That number is your fault code. Do not reset until you have noted it. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
48 High 6 Medium 3 Low
Just want the most common Atag E Range faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 57 documented codes

Tap any card for details

LED / flash-pattern codes
FILL (flashing)

Your boiler has lost water pressure and needs to be topped up to work at full capacity correctly.

Medium DIY-safe

What to check first

  1. Locate the external filling loop, usually a silver braided hose with one or two valves located underneath the boiler.
  2. Slowly open the valve(s) to allow mains water into the system until the pressure gauge reads between 1.0 and 1.5 bar.
  3. Close the valve(s) tightly and check for any leaks around the connection points.

Parts commonly replaced

  • Filling loop
  • Pressure relief valve
Full explanation for FILL (flashing)
flashing FILL / HIGH

Your boiler's water pressure has dropped too low, which is preventing it from working at its full heating capacity.

High DIY-safe

What to check first

  1. Locate the external filling loop, which is a silver braided hose connecting two pipes near your boiler.
  2. Open the valves at both ends of the hose slowly to allow water into the system.
  3. Watch the pressure gauge on the front of the boiler until the needle reaches 1.5 bar, then turn both valves firmly off.

Parts commonly replaced

  • Filling loop
  • Pressure gauge
  • Expansion vessel
Full explanation for flashing FILL / HIGH
Digital codes
10

Your boiler has stopped working because one of its internal sensors is sending incorrect information to the control system.

High Engineer only £120-220

Parts commonly replaced

  • Flow temperature sensor
  • Return temperature sensor
  • Wiring harness

Related codes

Full explanation for 10
12

Your boiler has encountered a deep internal communication problem within its computer control system and cannot operate.

High DIY-safe £250-500

What to check first

  1. Locate the power switch or fused spur for the boiler
  2. Turn off the power for 60 seconds
  3. Turn the power back on and press the 'Reset' button

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring Loom

Related codes

Full explanation for 12
13

Your boiler has experienced an internal computer error that is preventing it from starting up correctly.

High DIY-safe £250-500

What to check first

  1. Locate the Reset button on the control panel
  2. Press and hold the Reset button for 2-3 seconds
  3. Wait for the boiler to complete its restart sequence

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Control Panel Interface

Related codes

Full explanation for 13
14

Your boiler has encountered a computer processing error that is preventing it from starting up correctly.

High Engineer only £250-£450

Parts commonly replaced

  • Main PCB (Control Board)

Related codes

Full explanation for 14
15

Your boiler has encountered a computer or electronic processing fault that is preventing it from running safely.

High Engineer only £250-550

Parts commonly replaced

  • Main PCB (Control Board)
  • Wiring Harness

Related codes

Full explanation for 15
16

Your boiler has encountered a computer or electronic processing fault that is preventing it from heating your home.

High Engineer only £250-550

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Wiring harness

Related codes

Full explanation for 16
17

Your boiler has encountered a computer or communication error within its main control board, preventing it from running safely.

High DIY-safe £250-450

What to check first

  1. Switch the boiler off at the fused spur switch or main power supply.
  2. Wait for 30 seconds.
  3. Switch the power back on and press the 'Reset' button on the control panel.

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Wiring harness
Full explanation for 17
18

Your boiler has shut down because the water inside the unit has reached a temperature that is too hot to operate safely.

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves (TRVs) are turned to the highest setting
  2. Ensure the boiler pressure is between 1.0 and 1.5 bar
  3. Wait 30 minutes for the unit to cool down and then press the Reset button

Parts commonly replaced

  • Circulation Pump
  • NTC Temperature Sensor
  • Main Heat Exchanger (Flushing)

Related codes

Full explanation for 18
Showing 11–20 of 57
19

Your boiler has shut down because the water returning from your radiators is too hot, which usually means heat isn't being released into your rooms properly.

High DIY-safe £100-250

What to check first

  1. Check that at least two or three radiators have their valves fully open
  2. Ensure all Thermostatic Radiator Valves (TRVs) are turned up to a high setting
  3. Check that the internal pump is running if it is audible

Parts commonly replaced

  • Return temperature sensor (NTC)
  • Central heating pump
  • Bypass valve

Related codes

Full explanation for 19
20

Your boiler's internal computer has encountered a software or hardware conflict and has stopped working as a safety precaution.

High DIY-safe £250-550

What to check first

  1. Locate the 'Reset' button on the boiler control panel
  2. Press and hold the button for 2-3 seconds
  3. Wait to see if the error clears and the boiler restarts

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Wiring Loom

Related codes

Full explanation for 20
24

Your boiler's internal computer brain has detected a software or communication error and has stopped working to protect itself.

High DIY-safe £250-550

What to check first

  1. Switch the boiler off at the fused spur or power switch.
  2. Wait for 30 seconds.
  3. Switch the power back on and press the 'Reset' button.

Parts commonly replaced

  • Main PCB (Control Board)
  • Display PCB

Related codes

Full explanation for 24
28

Your boiler has stopped working because the internal fan, which safely pushes exhaust gases out of your home, is not spinning or communicating with the main control board.

High Engineer only £280-450

Parts commonly replaced

  • Fan assembly
  • Main PCB
  • Wiring harness
Full explanation for 28
30

Your boiler has detected that water is not circulating through the system properly, causing a large temperature gap between the water leaving and returning to the unit.

High DIY-safe £120-£350

What to check first

  1. Check that all radiator valves and boiler isolation valves are fully open.
  2. Ensure the system pressure is between 1.0 and 1.5 bar on the pressure gauge.
  3. Bleed all radiators to remove trapped air that might be blocking water flow.
  4. Restart the boiler by pressing the reset button.

Parts commonly replaced

  • Circulation pump
  • Flow and return thermistors
  • Central heating filter (cleaning/replacement)

Related codes

Full explanation for 30
31

Your boiler has detected an electrical fault with the internal sensor that monitors the temperature of the water leaving the unit, preventing it from heating safely.

High Engineer only £120-190

Parts commonly replaced

  • Flow temperature sensor (NTC)
  • Wiring harness
  • Control PCB

Related codes

Full explanation for 31
32

Your boiler has detected a fault with the pipe that measures the temperature of the water returning to the unit, causing it to stop running for safety.

High Engineer only £120-£200

Parts commonly replaced

  • Return water temperature sensor (NTC)
  • Wiring harness / Cable connections

Related codes

Full explanation for 32
34

Your boiler has stopped working because it cannot get a temperature reading from the pipe that returns water back into the unit.

High Engineer only £90-160

Parts commonly replaced

  • Return water temperature sensor (NTC)
  • Wiring harness
  • Control PCB

Related codes

Full explanation for 34
35

Your boiler's internal computer has encountered a software or communication glitch and needs to be restarted.

High DIY-safe £180-450

What to check first

  1. Press the Reset button on the control panel
  2. Turn the boiler power off at the fused spur switch for 30 seconds
  3. Turn the power back on and wait for the boiler to restart

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Display Control Unit

Related codes

Full explanation for 35
36

Your boiler's computer brain has encountered a confused internal signal and has stopped working as a safety precaution.

High DIY-safe £180-350

What to check first

  1. Locate the Reset button on the control panel
  2. Press and hold the Reset button for 2-3 seconds
  3. Wait for the boiler to restart and check if the code clears

Parts commonly replaced

  • Main PCB (Control Board)
  • Display PCB
Full explanation for 36
Showing 21–30 of 57
b18

Your boiler has switched itself off because the water inside it has become too hot, likely due to a circulation problem.

High DIY-safe £150-450

What to check first

  1. Check that all radiator valves are fully open
  2. Check the boiler pressure gauge and top up to 1.5 bar if low
  3. Check for any blocked or frozen external condensate pipes
  4. Press the Reset button once the boiler has cooled down

Parts commonly replaced

  • Circulation pump
  • Flow temperature sensor (NTC)
  • Main heat exchanger (flushing/cleaning)
Full explanation for b18
b19

Your boiler has shut down because the water returning from your radiators has become too hot, usually due to a lack of circulation through the system.

High DIY-safe £120-£350

What to check first

  1. Check that all radiator valves (TRVs) are turned to their highest setting
  2. Ensure the boiler pressure is between 1.0 and 1.5 bar on the gauge
  3. Check that the internal pump or any external zone valves are making a normal humming sound
  4. Restart the boiler using the reset button

Parts commonly replaced

  • Circulation pump
  • Return temperature sensor (NTC)
  • Main heat exchanger (flushing service)

Related codes

Full explanation for b19
b24

Your boiler has experienced an internal software or brain glitch that is preventing it from running safely.

High DIY-safe £250-450

What to check first

  1. Locate the power switch for the boiler and turn it off.
  2. Wait for approximately 30 seconds.
  3. Turn the power back on and press the Reset button on the control panel.

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Loom

Related codes

Full explanation for b24
b25

Your boiler is heating up too quickly and has shut itself down to prevent damage, usually because water isn't flowing through the system correctly.

High DIY-safe £120-£350

What to check first

  1. Check that at least two or three radiator valves are fully open
  2. Ensure the boiler pressure gauge is between 1.0 and 1.5 bar
  3. Check if the pump is making a humming sound, suggesting it is stuck

Parts commonly replaced

  • Circulation pump
  • Flow/Return thermistors
  • Main heat exchanger (flushing)

Related codes

Full explanation for b25
b26

Your boiler has stopped working because the water pressure is too low or the pump isn't circulating water through the system.

High DIY-safe £100-350

What to check first

  1. Check the pressure gauge on the front of the boiler
  2. If the pressure is below 1.0 bar, use the filling loop to top it up to 1.5 bar
  3. Reset the boiler once the correct pressure is reached

Parts commonly replaced

  • Circulation Pump
  • Water Pressure Sensor
  • Automatic Air Vent
Full explanation for b26
b28

Your boiler has switched itself off because the internal fan, which safely clears exhaust gases, is not spinning at the correct speed.

High Engineer only £180-450

Parts commonly replaced

  • Combustion Fan
  • Control PCB
  • Wiring harness
Full explanation for b28
b30

Your boiler has temporarily stopped because the water is heating up too quickly or isn't circulating around your radiators fast enough.

High DIY-safe £100-£350

What to check first

  1. Check that all radiator valves (TRVs) are turned to the highest setting
  2. Ensure the boiler pressure gauge is between 1.0 and 1.5 bar
  3. Check that any external valves on the pipework leading to the boiler are fully open

Parts commonly replaced

  • Circulation pump
  • Flow and return thermistors
  • Central heating filter (cleaning required)
Full explanation for b30
bL

Your boiler has detected that the water pressure is too low for it to operate safely and effectively.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver flexible hose) underneath your boiler.
  2. Slowly open the valve(s) until you hear water flowing and the pressure gauge rises.
  3. Close the valves tightly once the pressure reaches between 1.0 and 1.5 bar on the display.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure sensor
Full explanation for bL
Block 01

Your boiler has been automatically shut down because an external safety device, such as a separate room thermostat or a smoke alarm link, has triggered a signal to stop the system.

High Engineer only £120-250

Parts commonly replaced

  • External link bridge
  • Room thermostat
  • Interlock wiring
Full explanation for Block 01
Showing 31–40 of 57
Block 11

Your boiler has detected that the water inside is heating up much too quickly compared to how fast it is moving around your pipes, so it has temporarily paused your heating to prevent internal damage.

High Engineer only £150-300

Parts commonly replaced

  • Central heating pump
  • System filter
  • Diverter valve

Related codes

Full explanation for Block 11
Block 12

Your boiler has detected that the water is not flowing through the heating system as efficiently as it should while heating your hot water, causing it to temporarily pause that function.

Medium Engineer only £150-300

Parts commonly replaced

  • Diverter valve
  • Plate-to-plate heat exchanger
  • Central heating pump

Related codes

Full explanation for Block 12
Block 60

Your boiler’s internal computer has lost its correct settings for how much power it should be using, causing it to stop运行 to prevent damage.

High Engineer only £120-250

Parts commonly replaced

  • Control PCB
  • Gas Valve
Full explanation for Block 60
Block 67

Your boiler has detected an unusual temperature difference while it is supposed to be switched off, and it is pausing its operations until the system temperatures balance out.

Medium Engineer only £120-250

Parts commonly replaced

  • Flow/Return Temperature Sensor
  • Central Heating Pump
Full explanation for Block 67
Block 80

Your boiler has detected that the exhaust gases are becoming dangerously hot and has shut itself down to prevent internal damage.

High Engineer only £150-350

Parts commonly replaced

  • Heat exchanger
  • Flue gas temperature sensor
  • Burner assembly

Related codes

Full explanation for Block 80
Block 81

Your boiler has stopped working because it cannot detect a safety component that monitors exhaust fumes, which prevents it from firing up.

High Engineer only £120-250

Parts commonly replaced

  • Flue gas sensor
  • Wiring harness
  • PCB

Related codes

Full explanation for Block 81
Block 82

Your boiler has detected an electrical fault in its safety monitoring system and has automatically shut down to keep you safe.

High Engineer only £150-250

Parts commonly replaced

  • Flue gas sensor
  • Wiring harness

Related codes

Full explanation for Block 82
Block 85

Your boiler is struggling to detect the water flowing through it, so it has paused operation to run an automatic air-removal process to clear any trapped bubbles.

High Engineer only £120-250

Parts commonly replaced

  • Flow sensor
  • Circulating pump

Related codes

Full explanation for Block 85
Block 86

Your boiler has detected that the electricity supply coming into your home is unstable or fluctuating outside of normal limits.

Medium Engineer only

Parts commonly replaced

  • Control PCB
  • Power supply surge protection fuse

Related codes

Full explanation for Block 86
Showing 41–50 of 57
Err.L - Err.5

Your boiler is displaying a stored history of previous faults, which means it is currently reporting that it has encountered technical issues in the past.

Medium Engineer only

Parts commonly replaced

  • Control PCB
  • Wiring harness
  • Main circuit board
Full explanation for Err.L - Err.5
Error 00

Your boiler is failing to light the internal burner correctly, meaning it cannot produce heat or hot water.

High Engineer only £150-350

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame rectification probe
Full explanation for Error 00
Error 01

Your boiler has detected an electrical fault in its internal control circuit, which has caused it to shut down to prevent further damage.

High Engineer only £150-300

Parts commonly replaced

  • Control PCB
  • Wiring harness
  • External pump or diverter valve

Related codes

Full explanation for Error 01
Error 02

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

High Engineer only £150-350

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Ignition lead
Full explanation for Error 02
Error 03

Your boiler has detected that the internal components are getting too hot, so it has safely shut itself down to prevent damage.

High Engineer only £150-300

Parts commonly replaced

  • Temperature sensor
  • Fan
  • Heat exchanger seal

Related codes

Full explanation for Error 03
Error 04

Your boiler has detected an unstable power supply or a sudden electrical disruption, causing it to shut down for safety reasons.

High Engineer only £120-250

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for Error 04
Error 05

Your boiler's main computer brain is experiencing a critical error and can no longer safely operate the heating system.

High Engineer only £250-450

Parts commonly replaced

  • Control Unit/PCB
Full explanation for Error 05
Error 12

Your boiler has stopped working because an internal safety fuse responsible for the control power has blown, preventing the system from starting.

High Engineer only £120-220

Parts commonly replaced

  • 3AT internal fuse
  • Control PCB

Related codes

Full explanation for Error 12
Error 18

Your boiler has detected that the water inside has become dangerously hot and has shut itself down to prevent damage.

High Engineer only £150-300

Parts commonly replaced

  • Circulation pump
  • Flow sensor
  • Heat exchanger
  • PCB

Related codes

Full explanation for Error 18
Error 19

Your boiler has detected that the water returning to it is far too hot, causing it to shut down to prevent damage to the system.

High Engineer only £150-350

Parts commonly replaced

  • Return temperature sensor
  • Central heating pump
  • Plate heat exchanger

Related codes

Full explanation for Error 19
Showing 51–57 of 57
Error 28

Your boiler has switched itself off because it cannot detect that the internal fan, which is essential for clearing exhaust gases, is spinning correctly.

High Engineer only £200-350

Parts commonly replaced

  • Fan assembly
  • Wiring harness
  • Printed Circuit Board (PCB)
Full explanation for Error 28
Error 69

Your boiler has lost communication with its control screen, so it cannot show system information or respond to settings.

High Engineer only £150-300

Parts commonly replaced

  • Control interface
  • Connection cable
  • Main PCB
Full explanation for Error 69
Error 80

Your boiler has detected that the gases released during combustion are getting dangerously hot, so it has safely shut itself down to prevent damage.

High Engineer only £150-300

Parts commonly replaced

  • Flue gas temperature sensor
  • Heat exchanger
  • Primary flow sensor
Full explanation for Error 80
FILL

Your boiler has lost water pressure and needs to be topped up to work at full capacity.

Medium DIY-safe

What to check first

  1. Locate the filling loop (a silver flexi-hose) underneath the boiler or near your pipework.
  2. Open the valves on the filling loop to allow cold mains water to enter the system.
  3. Watch the pressure gauge on the boiler until the needle reaches the green zone (typically 1.2 to 1.5 bar).
  4. Close both valves tightly and remove the filling loop if required by your specific model.

Parts commonly replaced

  • Filling loop
  • Pressure relief valve
  • Pressure sensor
Full explanation for FILL
FILL (continuous)

Your boiler has stopped working because the water pressure inside your heating system has dropped too low.

High DIY-safe

What to check first

  1. Locate the external filling loop, which is usually a flexible metal hose connected to the system pipes near the boiler.
  2. Open the valves on both ends of the filling loop to allow water to enter the system until the pressure gauge reads between 1.0 and 1.5 bar.
  3. Fully close both valves and ensure the filling loop is disconnected if it is a removable type.

Parts commonly replaced

  • Pressure relief valve
  • Pressure sensor
Full explanation for FILL (continuous)
HIGH

Your boiler has automatically shut down because the internal water pressure has climbed too high to operate safely.

High DIY-safe

What to check first

  1. Locate a radiator in your home with a bleed valve.
  2. Place a cloth or small container under the valve.
  3. Open the bleed valve slowly to release water until the pressure gauge on your boiler drops to between 1.0 and 1.5 bar, then close the valve tightly.

Parts commonly replaced

  • Pressure relief valve
  • Filling loop
  • Pressure sensor
Full explanation for HIGH
STOP

Your boiler is telling you that the internal water pressure has successfully returned to the correct level after you topped it up.

Low DIY-safe

What to check first

  1. Check your boiler display to see if the message has cleared automatically
  2. If the boiler is still showing 'STOP', try pressing the reset button once
  3. Monitor the pressure gauge on the front of the boiler to ensure it remains between 1.0 and 2.0 bar
Full explanation for STOP