BoilerFaultCodes 09
General fault
Main Eco Compact Combi Fault codes & diagnostics
68 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Combi Natural Gas 25-30 kW 2019-present
Download the Main Eco Compact Combi manual
PDF
The fault code is already on your display
Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →
Severity at a glance
Each cell = one fault code. Hover to identify. 24 High
1 Medium
43 Unrated
Just want the most common Main Eco Compact Combi faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes
All 68 documented codes
Tap any card for details
15
General fault
20 Your boiler is struggling to control its internal gas supply, which means it has safely shut itself down to prevent any risk of incomplete combustion.
Your boiler is struggling to control its internal gas supply, which means it has safely shut itself down to prevent any risk of incomplete combustion.
Parts commonly replaced
- Gas valve
- PCB (Printed Circuit Board)
- Wiring harness
Related codes
28 Your boiler is struggling to control the gas supply it needs to stay lit, so it has shut down to keep your home safe.
Your boiler is struggling to control the gas supply it needs to stay lit, so it has shut down to keep your home safe.
Parts commonly replaced
- Gas valve
- Printed Circuit Board (PCB)
- Wiring harness
Related codes
40 Your boiler is struggling to manage the gas supply required to light the flame and heat your water, which has caused it to shut down for safety.
Your boiler is struggling to manage the gas supply required to light the flame and heat your water, which has caused it to shut down for safety.
Parts commonly replaced
- Gas valve
- PCB (Printed Circuit Board)
- Wiring harness
Related codes
103 Your boiler has lost communication with an optional safety monitoring device, which is preventing it from operating correctly.
Your boiler has lost communication with an optional safety monitoring device, which is preventing it from operating correctly.
Parts commonly replaced
- Safety Assist accessory module
- Wiring harness
- Main printed circuit board
Related codes
104 Your boiler has lost communication with an optional safety device, meaning it has shut down as a precaution to prevent unsafe operation.
Your boiler has lost communication with an optional safety device, meaning it has shut down as a precaution to prevent unsafe operation.
Parts commonly replaced
- Safety Assist module
- Wiring harness
- Main PCB
Related codes
107 Your boiler is having a communication error with an optional safety monitoring device, which is causing the system to stop functioning as a precaution.
Your boiler is having a communication error with an optional safety monitoring device, which is causing the system to stop functioning as a precaution.
Parts commonly replaced
- Safety Assist accessory module
- PCB
Related codes
109
General fault
110 Your boiler has detected that the water inside the heating system has become too hot and has automatically shut down to prevent damage.
Your boiler has detected that the water inside the heating system has become too hot and has automatically shut down to prevent damage.
Parts commonly replaced
- NTC Temperature Sensor
- Pump
- Primary Heat Exchanger
Related codes
Showing 11–20 of 68
118 Your boiler has stopped working because the water pressure inside the heating system has dropped too low to operate safely.
Your boiler has stopped working because the water pressure inside the heating system has dropped too low to operate safely.
What to check first
- Locate the external filling loop or internal key under the boiler
- Slowly open the valves to allow mains water to enter the system
- Watch the pressure gauge on the front of the boiler until the needle reaches the green zone between 1.0 and 1.5 bar
- Close the valves firmly and check that the fault code has cleared
Parts commonly replaced
- Filling loop
- Pressure relief valve
- Pressure sensor
Related codes
125 Your boiler is struggling to circulate water properly or is overheating because it cannot detect the expected changes in water temperature.
Your boiler is struggling to circulate water properly or is overheating because it cannot detect the expected changes in water temperature.
Parts commonly replaced
- Pump
- NTC Thermistor
- Heat Exchanger
Related codes
128 Your boiler has stopped because it cannot maintain a stable flame to heat your water.
Your boiler has stopped because it cannot maintain a stable flame to heat your water.
Parts commonly replaced
- Ignition electrode
- Gas valve
- Circuit board
Related codes
130
General fault
133 Your boiler is failing to light because it cannot detect a flame, which may be caused by a temporary gas supply issue.
Your boiler is failing to light because it cannot detect a flame, which may be caused by a temporary gas supply issue.
Parts commonly replaced
- Ignition electrode
- Gas valve
- PCB
Related codes
134 Your boiler is trying to start but cannot detect a flame, likely because the gas supply is blocked or the ignition system is failing to spark.
Your boiler is trying to start but cannot detect a flame, likely because the gas supply is blocked or the ignition system is failing to spark.
Parts commonly replaced
- Ignition electrode
- Gas valve
- PCB
Related codes
135 Your boiler is failing to light because it is not receiving enough gas or is having trouble sparking, meaning you currently have no heating or hot water.
Your boiler is failing to light because it is not receiving enough gas or is having trouble sparking, meaning you currently have no heating or hot water.
Parts commonly replaced
- Ignition electrode
- Gas valve
- Printed Circuit Board (PCB)
Related codes
160 Your boiler has detected an issue with the system that controls the flow of gas, meaning it has shut itself down to keep your home safe.
Your boiler has detected an issue with the system that controls the flow of gas, meaning it has shut itself down to keep your home safe.
Parts commonly replaced
- Gas valve
- Printed Circuit Board (PCB)
- Wiring harness
Related codes
321 Your boiler is having trouble controlling the flow of gas needed to stay lit, so it has shut down as a safety precaution.
Your boiler is having trouble controlling the flow of gas needed to stay lit, so it has shut down as a safety precaution.
Parts commonly replaced
- Gas valve
- PCB (Printed Circuit Board)
- Wiring harness
Related codes
384
General fault
Showing 21–30 of 68
Bat
errors related to the optional Safety Assist accessory
C
Fan connections check at fan & PCB X11 and X23 connectors
D
Temperature sensor faulty
E
Gas at burner / gas valve check
E01
Gas supply failure
E04
Gas supply failure
E05
Central heating NTC fault
E06
Domestic hot water NTC fault
E10
Primary circuit low pressure
E12
Circulation fault (primary)
Showing 31–40 of 68
E13
Circulation fault
E14
Flow NTC fault
E15
Interruption of gas supply or flame failure
E16
Interruption of gas supply (internal error)
E17
Flow / return sensor temperature test
E19
Fan or fan wiring fault
E20 Your boiler has detected a fault with the internal sensor that monitors the temperature of your central heating water, causing the system to stop working as a safety precaution.
Your boiler has detected a fault with the internal sensor that monitors the temperature of your central heating water, causing the system to stop working as a safety precaution.
Parts commonly replaced
- Central heating NTC temperature sensor
- Connecting wiring harness
Related codes
E21
Flue failure
E22
Hot water sensor failure
E24
Hot water sensor failure
Showing 41–50 of 68
E27
Combustion error
E108
Primary circuit low pressure
E110 Your boiler has switched itself off because it has reached an unsafe temperature, usually due to a lack of water flow or a circulation problem.
Your boiler has switched itself off because it has reached an unsafe temperature, usually due to a lack of water flow or a circulation problem.
What to check first
- Check if your radiator valves are open
- Check the boiler pressure gauge and top up to 1.5 bar if low
- Press the 'R' or 'Reset' button for 2 seconds once the boiler has cooled down
Parts commonly replaced
- Overheat Thermostat
- Circulation Pump
- Internal Pipework (unblocking)
Related codes
E117
Primary circuit low pressure
E118 Your boiler has stopped working because the water pressure in the system has dropped too low and needs topping up.
Your boiler has stopped working because the water pressure in the system has dropped too low and needs topping up.
What to check first
- Locate the filling loop (usually two braided silver hoses or blue levers) underneath the boiler.
- Open the valves slowly until you hear water entering the system.
- Watch the pressure gauge and close the valves tightly once the needle reaches 1.5 bar.
Parts commonly replaced
- Filling loop
- Expansion vessel
- Pressure relief valve
E125 Your boiler is struggling to move hot water around the system, which is usually caused by a blockage or a pump issue that is preventing the unit from cooling itself down.
Your boiler is struggling to move hot water around the system, which is usually caused by a blockage or a pump issue that is preventing the unit from cooling itself down.
What to check first
- Check that all radiator valves are fully open
- Ensure the boiler pressure is between 1.0 and 1.5 bar on the gauge
- Gently bleed air from your radiators using a radiator key
Parts commonly replaced
- Circulation pump
- Plate heat exchanger
- Main heat exchanger
Related codes
E127
Circulation fault (primary)
E128 Your boiler has lost its flame while running, which means it has safely shut down to prevent issues.
Your boiler has lost its flame while running, which means it has safely shut down to prevent issues.
What to check first
- Check if other gas appliances, like a hob, are working to confirm gas supply
- Ensure your pre-pay gas meter has sufficient credit
- Press and hold the Reset button for five seconds
Parts commonly replaced
- Ignition electrode
- Flame sensing electrode
- Gas valve
- Condensate trap
Related codes
E130 Your boiler has shut down because a sensor has detected that the exhaust gases are becoming too hot, which is a safety feature to prevent damage.
Your boiler has shut down because a sensor has detected that the exhaust gases are becoming too hot, which is a safety feature to prevent damage.
Parts commonly replaced
- Flue NTC sensor
- Main heat exchanger (cleaning or replacement)
- Burner insulation
Related codes
E133 Your boiler has failed to light because it is not receiving enough gas or cannot detect the flame used to heat your water.
Your boiler has failed to light because it is not receiving enough gas or cannot detect the flame used to heat your water.
What to check first
- Check if other gas appliances, like a cooker hob, are working to confirm your gas supply is active.
- If you have a prepayment meter, check that you have enough credit.
- Locate the white pipe beneath the boiler and ensure it hasn't frozen if the weather is very cold.
- Press the 'Reset' button for five seconds to see if the boiler restarts.
Parts commonly replaced
- Gas Valve
- Ignition Electrode
- Printed Circuit Board (PCB)
- Condensate Pipework
Related codes
Showing 51–60 of 68
E160 Your boiler has stopped working because the internal fan, which safely exhausts gases, is not spinning at the correct speed or has lost power.
Your boiler has stopped working because the internal fan, which safely exhausts gases, is not spinning at the correct speed or has lost power.
Parts commonly replaced
- Fan assembly
- Fan wiring harness
- Main circuit board (PCB)
Related codes
E193
Circulation fault (primary)
E220
Safety thermostat operated
E227
Flame failure
E260
Fan or fan wiring fault
E320
Central heating NTC fault
E321 Your boiler has detected a problem with the sensor that monitors the temperature of your hot water, meaning your taps may not get as hot as they should or stay consistent.
Your boiler has detected a problem with the sensor that monitors the temperature of your hot water, meaning your taps may not get as hot as they should or stay consistent.
Parts commonly replaced
- Hot water NTC temperature sensor
- Wiring harness
Related codes
E327
Central heating NTC fault
E384 Your boiler thinks a flame is present even when it should be off, causing it to shut down for safety.
Your boiler thinks a flame is present even when it should be off, causing it to shut down for safety.
Parts commonly replaced
- Flame sensing electrode
- Ignition lead
- Printed Circuit Board (PCB)
Related codes
E385
External error
Showing 61–68 of 68
F
Ignition electrode and lead / electrode connection / spark gap and position
G
Check gas valve supply pressure and CO2 values / flame sensing electrode
H
Safety thermostat operated or faulty system
I
CH system pressure less than 0.5 bar
J
Flow temperature sensor / air in system
K
Diverter valve motor / PCB X13 connector
L
Mains water filter & assembly / Hall Effect Sensor
M
Temperature sensors faulty or heat exchanger obstruction
Status & diagnostic codes 3 operating states & engineer diagnostics
Not faults — these are normal operating states. Tap to expand.
3 operating states & engineer diagnostics
Not faults — these are normal operating states. Tap to expand.
C13 Diagnostic Your boiler is struggling to bring enough fresh air in or push exhaust gases out, which has triggered a safety shut-down to prevent harmful fumes from entering your home. G20 Diagnostic Your boiler is displaying a setting notification indicating that it is configured to run on natural gas, which is the standard fuel type for UK homes. IPX5D Diagnostic This code is not a fault; it simply indicates that your boiler's casing meets the official safety standard for protection against moisture and water spray.
Boiler cover options
Avoid the next call-out bill
Monthly cover means no unexpected bills when your boiler breaks down.
Approved partner
Get a quote →
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Affiliate links. We may earn a commission at no extra cost to you.