Main Eco Elite Fault codes & diagnostics

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

Combi Natural Gas 24-28 kW 2013-2016 Discontinued

Replaced by: Main Eco Compact

Download the Main Eco Elite manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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.
30 High 2 Medium 4 Low
Just want the most common Main Eco Elite faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 36 documented codes

Tap any card for details

LED / flash-pattern codes
1 red flash

Your boiler has likely overheated or a sensor has detected an issue with how water is flowing through the system.

High DIY-safe £90-220

What to check first

  1. Check that your radiator valves are open
  2. Ensure there are no blockages in the system
  3. Turn the selector switch to the reset position for five seconds and then back to the desired mode

Parts commonly replaced

  • Temperature Sensor (NTC)
  • Water Pressure Switch
  • Circulation Pump

Related codes

Full explanation for 1 red flash
2 red flashes

Your boiler has become too hot and has shut itself down for safety reasons.

High DIY-safe £100-350

What to check first

  1. Ensure all radiator valves (TRVs) are open to allow water to circulate
  2. Check that your system pressure is between 1.0 and 1.5 bar on the gauge
  3. Wait for the boiler to cool down and then turn the selector switch to 'R' for five seconds to reset

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Heat Exchanger

Related codes

Full explanation for 2 red flashes
3 green flashes

Your boiler is struggling to keep its flame lit and is currently trying to fix itself automatically before shutting down.

Medium Engineer only £90-280

Parts commonly replaced

  • Ignition electrode
  • Flame sensing probe
  • Gas valve
  • Condensate trap

Related codes

Full explanation for 3 green flashes
3 red flashes

Your boiler has failed to light several times and has now locked itself out for safety.

High DIY-safe £100-£250

What to check first

  1. Check that your gas supply is turned on at the meter
  2. Check if other gas appliances in your home are working
  3. Press and hold the selector switch in the 'reset' position for 5 seconds

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Spark Generator

Related codes

Full explanation for 3 red flashes
4 green flashes

Your boiler is having a temporary 'handshake' problem between its internal computers and will usually try to fix itself automatically.

Low DIY-safe £0-280

What to check first

  1. Wait for 30 minutes to see if the error clears itself as it is a temporary communication fault
  2. Turn the selector switch to the reset position for five seconds
  3. Switch the main electrical power to the boiler off and back on again

Parts commonly replaced

  • None (usually self-resets)
  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for 4 green flashes
4 red flashes

Your boiler's internal fan, which safely removes waste gases, is not spinning or starting correctly, causing the system to shut down for safety.

High Engineer only £200-£450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Air pressure switch

Related codes

Full explanation for 4 red flashes
5 green flashes

Your boiler is experiencing a temporary computer glitch while trying to read its internal settings and will attempt to fix itself shortly.

Low DIY-safe £0-280

What to check first

  1. Wait for the boiler to automatically reset itself
  2. If the flashing continues, turn the selector switch to the reset position for 5 seconds
  3. Monitor the boiler to ensure it returns to normal operation

Parts commonly replaced

  • No parts usually required
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 5 green flashes
5 red flashes

Your boiler's internal memory chip has developed a communication fault, meaning the control board can no longer remember its specific operating settings.

High Engineer only £180-350

Parts commonly replaced

  • Parameter Storage Unit (PSU)
  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for 5 red flashes
6 green flashes

Your boiler has encountered a minor, temporary glitch and is currently pausing before trying to restart itself automatically.

Low DIY-safe £0-80

What to check first

  1. Wait for the boiler to complete its self-reset process
  2. If the flashing continues for more than 10 minutes, turn the selector switch to the reset position for five seconds
  3. Check that your credit or prepaid gas meter has sufficient funds

Parts commonly replaced

  • No parts usually required
  • Flame sensing electrode

Related codes

Full explanation for 6 green flashes
6 red flashes

Your boiler has likely experienced a flame failure or ignition problem, meaning it cannot detect the fire required to heat your water.

High DIY-safe £120-280

What to check first

  1. Check that your gas prepay meter has credit
  2. Ensure other gas appliances in your home, like a hob, are working correctly
  3. Turn the selector switch to the reset position for five seconds and then back to 'On'

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Probe
  • Gas Valve

Related codes

Full explanation for 6 red flashes
Showing 11–20 of 36
FLASH FLASH ON

Your boiler's fan, which safely pushes exhaust fumes outside, has stopped working or is not spinning at the correct speed.

High Engineer only £250-450

Parts commonly replaced

  • Fan assembly
  • Air pressure switch
  • Main PCB

Related codes

Full explanation for FLASH FLASH ON
FLASH OFF FLASH

Your boiler has stopped working because the electricity supply reaching it is too low to run the internal components safely.

High DIY-safe £100-350

What to check first

  1. Check if there is a regional power cut or if other appliances in your home are flickering.
  2. Ensure the boiler's fused spur switch is fully turned on and the plug is pushed in properly.
  3. If you use a prepaid electric meter, check that you have sufficient credit remaining.

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • External Voltage Stabiliser
  • Electrical Wiring

Related codes

Full explanation for FLASH OFF FLASH
FLASH OFF ON

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

High DIY-safe £100-280

What to check first

  1. Check that all radiator valves are fully open to allow water to circulate
  2. Ensure your system pressure is topped up to between 1 and 1.5 bar
  3. Turn the selector switch to the reset position for five seconds and then back to heat/hot water

Parts commonly replaced

  • Overheat Thermostat
  • Circulating Pump
  • Main Heat Exchanger
  • Temperature Sensors (NTC)

Related codes

Full explanation for FLASH OFF ON
FLASH ON FLASH

Your boiler's internal computer has developed a fault and can no longer control the heating system correctly.

High Engineer only £280-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for FLASH ON FLASH
FLASH ON ON

Your boiler’s internal control computer has developed a fault and can no longer manage the heating system safely.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for FLASH ON ON
ON FLASH FLASH

Your boiler has detected that water is not moving through the system correctly or there isn't enough water inside the unit to operate safely.

High DIY-safe £120-350

What to check first

  1. Check the pressure gauge on the front of the boiler; if it is below 1.0 bar, use the filling loop to top it up to 1.5 bar.
  2. Ensure all radiator valves and isolation valves under the boiler are fully open.
  3. Gently bleed your radiators to remove any trapped air that might be blocking water flow.

Parts commonly replaced

  • Circulation pump
  • Water pressure switch
  • Heat exchanger

Related codes

Full explanation for ON FLASH FLASH
ON FLASH ON

Your boiler's internal temperature sensors are giving an incorrect reading, which means the system cannot safely heat your water.

High Engineer only £90-160

Parts commonly replaced

  • NTC Thermistor
  • Temperature Sensor
  • Wiring Harness

Related codes

Full explanation for ON FLASH ON
ON OFF FLASH

Your boiler has detected that the electrical wiring coming from your home’s power supply is connected the wrong way around.

High Engineer only £80-130

Parts commonly replaced

  • External wiring connection
  • Printed Circuit Board (PCB)

Related codes

Full explanation for ON OFF FLASH
ON ON FLASH

Your boiler's internal computer has encountered a critical error and needs a professional electronic inspection.

High Engineer only £280-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for ON ON FLASH
Digital codes
110

Your boiler has switched itself off because it has gotten too hot, likely due to trapped air or a blockage stopping water from circulating properly.

High DIY-safe £100-280

What to check first

  1. Turn off the boiler and allow it to cool down completely.
  2. Use a radiator key to bleed all radiators and remove trapped air.
  3. Check the boiler pressure gauge and top it up to 1.5 bar if it has dropped.
  4. Press the 'Reset' button on the boiler control panel.

Parts commonly replaced

  • Circulation Pump
  • Overheat Thermostat
  • NTC Temperature Sensor

Related codes

Full explanation for 110
Showing 21–30 of 36
119

Your boiler has stopped working because the water pressure in the central heating system has dropped too low to operate safely.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (a flexible silver hose) underneath or near the boiler.
  2. Open the one or two small taps on the filling loop until you hear water entering the system.
  3. Watch the pressure gauge and close the taps once the needle reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve

Related codes

Full explanation for 119
125

Your boiler has detected that water is failing to move through the system correctly, which could be caused by air locks, a blockage, or a pump issue.

High DIY-safe £180-450

What to check first

  1. Check if your radiator valves are open
  2. Ensure the system pressure is between 1.0 and 1.5 bar
  3. Gently bleed your radiators to remove trapped air

Parts commonly replaced

  • Circulation pump
  • Flow temperature sensor
  • Automatic air vent

Related codes

Full explanation for 125
127

Your boiler has failed to heat the water to a high enough temperature to complete its automatic routine cleaning cycle that prevents bacteria growth.

Low DIY-safe £0-120

What to check first

  1. Check that your hot water temperature dial is set to its normal operating position, not at its lowest.
  2. Ensure the boiler has been left switched on consistently so it can complete its timed weekly heat cycle.
  3. Restart the boiler using the reset button to see if the cycle completes successfully on the next attempt.

Parts commonly replaced

  • No parts usually required
  • Hot water temperature sensor (NTC thermistor)
  • Diverter valve

Related codes

Full explanation for 127
133

Your boiler has tried to light several times but cannot create a steady flame, causing it to shut down for safety.

High DIY-safe £100-280

What to check first

  1. Check that your gas pre-payment meter (if applicable) has credit.
  2. Ensure your external gas emergency control valve is in the 'on' position.
  3. Hold the selector switch to 'R' for five seconds to attempt a reset.
  4. If it is freezing outside, check that your white plastic condensate pipe hasn't frozen.

Parts commonly replaced

  • Spark electrode
  • Gas valve
  • Ignition lead
  • PCB

Related codes

Full explanation for 133
160

Your boiler has stopped working because the internal fan, which safely pushes exhaust gases out of the flue, is not running at the correct speed.

High Engineer only £220-£450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for 160
E1

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

High DIY-safe £100-250

What to check first

  1. Turn off the boiler and allow it to cool down completely.
  2. Breathe any trapped air out of your radiators using a radiator key.
  3. Check the boiler pressure gauge and top it up to 1.5 bar if it has dropped.
  4. Reset the boiler by turning the selector switch to 'R' for at least five seconds.

Parts commonly replaced

  • Overheat Thermostat
  • Circulating Pump
  • NTC Thermistor

Related codes

Full explanation for E1
E2

Your boiler is struggling to push water around your radiators, usually because of trapped air or a blockage.

High DIY-safe £80-250

What to check first

  1. Turn off your heating and allow the radiators to cool down.
  2. Use a radiator key to bleed all radiators, starting from the lowest floor.
  3. Check your boiler pressure gauge and use the filling loop to top it up to 1.5 bar if it has dropped.

Parts commonly replaced

  • Circulation Pump
  • Auto Air Vent
  • Main Heat Exchanger (if scaled)

Related codes

Full explanation for E2
E3

Your boiler's electronic control centre has developed an internal error and can no longer safely operate the system.

High Engineer only £250-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
Full explanation for E3
E20

Your boiler has lost its connection to the sensor that measures the temperature of the water for your radiators, meaning it cannot heat your home safely.

High Engineer only £90-160

Parts commonly replaced

  • Central Heating (Flow) NTC Thermistor
  • Connecting wiring harness

Related codes

Full explanation for E20
E28

Your boiler's computer system is currently reporting that it is not compatible with the specific version of the internal control board installed, meaning it cannot safely operate your heating or hot water.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for E28
Showing 31–36 of 36
E50

Your boiler has detected a problem with the sensor that measures hot water temperature, which means it may not be able to heat your taps correctly.

Medium Engineer only £90-160

Parts commonly replaced

  • Hot water NTC thermistor
  • Connecting wiring harness

Related codes

Full explanation for E50
E110

Your boiler has likely overheated, causing a safety sensor to shut the system down to prevent damage.

High DIY-safe £100-280

What to check first

  1. Wait 30 minutes for the boiler to cool down fully.
  2. Check that your radiator valves are open and not blocked by furniture.
  3. Check the boiler pressure gauge and top it up to 1.5 bar if it is too low.
  4. Turn the selector switch to the 'R' (Reset) position for at least five seconds and then release it.

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Water Pressure Sensor

Related codes

Full explanation for E110
E119

Your boiler has stopped working because the water pressure is too low for the system to run safely.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually two silver braided hoses under the boiler)
  2. Open the valves slowly until you hear water entering the system
  3. Watch the pressure gauge and close the valves once it reaches between 1.0 and 1.5 bar

Parts commonly replaced

  • Filling loop
  • Water pressure switch
  • Expansion vessel

Related codes

Full explanation for E119
E125

Your boiler has detected that water is not moving through the system properly, which is causing it to overheat and shut down for safety.

High Engineer only £180-£450

Parts commonly replaced

  • Circulation pump
  • Diverter valve motor
  • Main heat exchanger (flushing)

Related codes

Full explanation for E125
E133

Your boiler has tried to ignite but cannot get a steady gas supply or sense a flame, which means it has locked itself out for safety.

High DIY-safe £100-£250

What to check first

  1. Check if your gas meter has credit (if on a prepayment meter)
  2. Check if other gas appliances, like a hob, are working to confirm gas supply
  3. Rotate the selector switch to the 'R' (Reset) position for five seconds and release
  4. If it is freezing outside, check if your white plastic condensate pipe is frozen and thaw it with warm water

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E133
E160

Your boiler has detected a problem with the fan that clears exhaust gases, preventing it from starting up safely.

High Engineer only £180-£400

Parts commonly replaced

  • Extraction Fan
  • Fan Wiring Harness
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E160
Status & diagnostic codes

1 operating states & engineer diagnostics

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

1 green flash Status Your boiler has reached its set temperature and is temporarily pausing its operation as a normal part of its heating cycle.