Vaillant ecoMAX Pro 28E Fault codes & diagnostics

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

Combi Natural Gas 28 kW 2000-2005 Discontinued

Replaced by: ecoTEC Pro

Download the Vaillant ecoMAX Pro 28E 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.
28 High 1 Medium
Just want the most common Vaillant ecoMAX Pro 28E faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 29 documented codes

Tap any card for details

F.1

Your boiler has failed to ignite and is not producing heat, which is usually due to an interrupted gas supply or a problem with the internal spark system.

High DIY-safe £100-280

What to check first

  1. Check if other gas appliances, like a cooker, are working to confirm gas is reaching the property
  2. Ensure your gas meter has credit if you use a pre-payment account
  3. Press the reset button (indicated by a flame with a line through it) and hold for two seconds

Parts commonly replaced

  • Ignition electrode
  • Spark generator
  • Gas valve

Related codes

Full explanation for F.1
F.4

Your boiler is failing to light the flame properly, which means it cannot heat your radiators or water.

High DIY-safe £100-280

What to check first

  1. Check if your gas supply is turned on at the meter
  2. Check if other gas appliances in your home are working correctly
  3. Press the reset button (flame symbol with a cross) for one second

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Electrode
  • Gas Valve
  • Ignition Lead

Related codes

Full explanation for F.4
F.5

Your boiler has got too hot and has automatically shut down for safety to prevent damage.

High DIY-safe £120-280

What to check first

  1. Turn off the boiler and wait 20 minutes for it to cool down.
  2. Ensure all radiator valves and the boiler's isolation valves are fully open.
  3. Locate the reset button (often marked with a flame symbol or 'R') and press it once.

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • NTC Sensor

Related codes

Full explanation for F.5
F.6

Your boiler has stopped working because a sensor that measures the temperature of the water leaving the unit has stopped sending a reliable signal.

High Engineer only £90-160

Parts commonly replaced

  • Flow NTC Thermistor
  • Wiring Harness

Related codes

Full explanation for F.6
F.10

Your boiler is currently unable to read the temperature of the water returning to it, which means it has stopped working to prevent potential damage.

High Engineer only £120-220

Parts commonly replaced

  • Return NTC thermistor
  • Wiring harness

Related codes

Full explanation for F.10
F.11

Your boiler's electronic control systems have stopped talking to each other, which prevents the unit from starting or running your heating and hot water.

High Engineer only £150-350

Parts commonly replaced

  • Interface cable
  • Display interface
  • Main PCB

Related codes

Full explanation for F.11
F.12

Your boiler's main control panel is failing to communicate with the internal electronic board, meaning the system cannot receive commands to heat your home or water.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
  • Interface display unit

Related codes

Full explanation for F.12
F.13

Your boiler's internal computer has detected a problem with its electronic control system, causing the unit to shut down for safety reasons.

High Engineer only £250-450

Parts commonly replaced

  • Main printed circuit board (PCB)

Related codes

Full explanation for F.13
F.17

Your boiler has detected that the electrical wiring is connected incorrectly or there is a problem with the mains power supply.

High Engineer only £80-160

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • External electrical socket or fused spur

Related codes

Full explanation for F.17
F.20

Your boiler's internal computer chips are failing to talk to each other properly, meaning the system has shut down to prevent incorrect operation.

High Engineer only £150-350

Parts commonly replaced

  • Main PCB
  • Display Interface Module

Related codes

Full explanation for F.20
Showing 11–20 of 29
F.24

Your boiler has stopped working because the water isn't circulating properly, likely due to a pump issue or trapped air in the system.

High Engineer only £180-£350

Parts commonly replaced

  • Circulation pump
  • Automatic air vent
  • Pump cable

Related codes

Full explanation for F.24
F.25

Your boiler is overheating because water is not flowing through it properly, which has triggered a safety shutdown to prevent damage.

High Engineer only £150-350

Parts commonly replaced

  • Central heating pump
  • NTC thermistor
  • Flow sensor

Related codes

Full explanation for F.25
F1

Your boiler has tried to start but could not create or detect a flame, causing it to shut down for safety.

High DIY-safe £100-£350

What to check first

  1. Check if your gas supply is active by testing another gas appliance like a hob.
  2. Ensure your gas meter has credit if you use a pre-payment meter.
  3. Press the reset button (indicated by a flame with a cross through it) for three seconds.

Parts commonly replaced

  • Ignition lead
  • Electrode set
  • Gas valve
  • PCB

Related codes

Full explanation for F1
F4

Your boiler has failed to keep the flame lit and has locked itself out for safety.

High DIY-safe £100-£280

What to check first

  1. Check that your gas supply is turned on and other gas appliances are working.
  2. If you have a pre-payment meter, ensure you have sufficient credit.
  3. Press the Reset button (the flame symbol with a cross) for one second to see if the boiler restarts.

Parts commonly replaced

  • Ignition electrode
  • Flame sensing electrode
  • Gas valve
Full explanation for F4
F5

Your boiler has got too hot and stopped working to protect itself, likely because the water isn't moving through the system properly.

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 and 1.5 bar on the gauge
  3. Press the 'Reset' button (flame symbol with a cross) to restart the appliance

Parts commonly replaced

  • Circulation pump
  • Overheat thermostat
  • Heat exchanger

Related codes

Full explanation for F5
F6

Your boiler has lost its ability to measure the temperature of the water leaving the unit, usually due to a faulty sensor or a wiring issue.

High Engineer only £90-160

Parts commonly replaced

  • Central heating flow NTC thermistor
  • Wiring harness connector

Related codes

Full explanation for F6
F10

Your boiler has lost signal from the sensor that monitors the temperature of the water returning from your radiators.

High Engineer only £90-160

Parts commonly replaced

  • Central heating return NTC thermistor
  • Wiring harness / connector

Related codes

Full explanation for F10
F11

Your boiler's main internal computer is having trouble communicating with its electronic components, meaning it cannot process instructions to provide heat.

High Engineer only £180-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for F11
F12

Your boiler's main control panel is having trouble communicating with the internal display or remote controls.

High DIY-safe £120-280

What to check first

  1. Switch the boiler off at the fused spur power switch
  2. Wait 60 seconds
  3. Switch the power back on to see if the connection resets

Parts commonly replaced

  • User interface display
  • Wiring harness
  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for F12
F13

Your boiler's computer brain has encountered a serious communication error and can no longer control the heating system safely.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness
Full explanation for F13
Showing 21–29 of 29
F14

Your boiler has shut down because it has detected that the water inside is getting much too hot, which is usually caused by a circulation problem.

High DIY-safe £150-£450

What to check first

  1. Check that your radiator valves are fully open to allow water to flow.
  2. Ensure your system pressure is topped up to between 1 and 1.5 bar on the gauge.
  3. Try resetting the boiler to see if the error clears once the water cools down.

Parts commonly replaced

  • Circulation pump
  • NTC thermistor (Flow sensor)
  • Main heat exchanger

Related codes

Full explanation for F14
F16

Your boiler thinks it still sees a flame even though it has commanded the burner to turn off, which is a safety concern that prevents it from restarting.

High Engineer only £120-350

Parts commonly replaced

  • Ionisation electrode
  • Gas valve
  • PCB (Printed Circuit Board)
Full explanation for F16
F17

Your boiler has detected that the electrical supply coming into the unit is currently too low for it to operate safely.

High Engineer only £100-£350

Parts commonly replaced

  • Main PCB
  • External Power Supply Cable

Related codes

Full explanation for F17
F18

Your boiler's control panel has lost communication with the internal system, preventing you from adjusting settings or seeing the boiler's status.

Medium DIY-safe £120-280

What to check first

  1. Locate the main power switch for the boiler (fused spur).
  2. Turn the power off for 60 seconds.
  3. Turn the power back on to see if the control panel restarts and clears the error.

Parts commonly replaced

  • User interface (display board)
  • Wiring harness
  • Main Printed Circuit Board (PCB)
Full explanation for F18
F19

Your boiler has lost connection with a temperature sensor, meaning it cannot safely monitor the heat of the water going to your radiators.

High Engineer only £90-160

Parts commonly replaced

  • Flow/Return NTC Thermistor
  • Wiring Harness
  • Sensor Connection Clips

Related codes

Full explanation for F19
F20

Your boiler's internal computer chips are unable to communicate properly due to a software version mismatch.

High Engineer only £280-550

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • User Interface (MMI) Board

Related codes

Full explanation for F20
F24

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

High DIY-safe £120-£350

What to check first

  1. Ensure all radiator valves (TRVs) are turned to the highest setting
  2. Check that the boiler pressure is between 1.0 and 1.5 bar on the gauge
  3. Gently bleed your radiators to remove trapped air

Parts commonly replaced

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

Related codes

Full explanation for F24
F25

Your boiler is heating up too quickly, causing it to shut down to prevent damage from overheating.

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the central heating system pressure is between 1.0 and 1.5 bar
  3. Bleed all radiators to remove trapped air that might be blocking water flow

Parts commonly replaced

  • Circulation Pump
  • NTC Temperature Sensors
  • Main Heat Exchanger (Descaling)

Related codes

Full explanation for F25
F26

Your boiler has detected that the water is heating up far too quickly or there is a blockage preventing hot water from flowing out of the unit.

High DIY-safe £150-450

What to check first

  1. Ensure all radiator valves and lockdowns are fully open
  2. Check that the external filling loop valves are closed properly
  3. Reset the boiler to see if the error clears once the system has cooled down

Parts commonly replaced

  • Circulation Pump
  • Bypass Valve
  • Flow/Return NTC Thermistors

Related codes

Full explanation for F26