Vaillant ecoMAX 824E Fault codes & diagnostics

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

Combi Natural Gas 24 kW 2000-2005 Discontinued
GC Numbers 47-044-0747-044-12

Replaced by: ecoTEC plus 824

Download the Vaillant ecoMAX 824E manualThe official installation and service manual (PDF), the document these fault codes were read from. PDF

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Severity at a glance

Each cell = one fault code. Hover to identify.
1 Emergency 16 High 3 Medium 6 Low
Just want the most common Vaillant ecoMAX 824E faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 26 documented codes

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0

Your boiler is currently on standby because your thermostat, timer, or smart heating controls are not telling it to turn on.

High DIY-safe

What to check first

  1. Check that your room thermostat or smart controller is switched on and set to a higher temperature than the current room temperature.
  2. Replace the batteries in your wireless room thermostat or timer.
  3. Check that any external programmer or time clock is set to the correct 'on' schedule.

Parts commonly replaced

  • Room thermostat
  • Time clock or programmer
  • Wiring centre

Related codes

Full explanation for 0
1

Your boiler is temporarily locked out because it has detected a problem with the internal fan that safely clears combustion gases.

High Engineer only £150-£300

Parts commonly replaced

  • Boiler fan
  • Air pressure switch
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 1
2

Your boiler is temporarily clearing out leftover gases from the combustion chamber before attempting to safely light.

Low Engineer only

Related codes

Full explanation for 2
3

Your boiler has failed to light its flame, meaning it cannot provide you with heating or hot water at the moment.

High Engineer only £150-300

Parts commonly replaced

  • Ignition lead
  • Ignition electrode
  • Gas valve
  • PCB

Related codes

Full explanation for 3
5

Your boiler is currently busy heating your hot water taps or shower, which is a normal operation rather than an error.

Low Engineer only

Related codes

Full explanation for 5
6

Your boiler has temporarily stopped heating your home or water because a safety control has triggered, usually due to a temporary build-up of heat.

Medium DIY-safe £90-200

What to check first

  1. Check that your heating and hot water controls are not set too high.
  2. Ensure all your radiator valves are fully open so water can circulate properly.
  3. Try resetting the boiler using the reset button once it has had time to cool down.

Parts commonly replaced

  • NTC thermistor
  • PCB
  • Automatic bypass valve

Related codes

Full explanation for 6
7

Your boiler is safely running its pump a little longer than usual to clear any leftover heat, but it is not preventing your heating from working.

Low Engineer only £90-180

Parts commonly replaced

  • Circulation pump
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 7
8

Your boiler is taking a brief enforced rest between heating cycles to protect itself from excessive wear and tear.

Low Engineer only

Related codes

Full explanation for 8
Showing 11–20 of 26
E11

Your boiler has temporarily stopped working because it has detected a disagreement between its internal temperature sensors.

High Engineer only £150-£300

Parts commonly replaced

  • NTC thermistor
  • Main PCB

Related codes

Full explanation for E11
E12

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

High DIY-safe

What to check first

  1. Locate the filling loop beneath your boiler.
  2. Open the valves gently to let water into the system until the pressure gauge reads between 1.0 and 1.5 bar.
  3. Close both valves firmly and check the pressure.

Parts commonly replaced

  • Pressure sensor
  • Filling loop
  • Expansion vessel

Related codes

Full explanation for E12
E13

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

High DIY-safe £0-£120

What to check first

  1. Locate the filling loop (usually two valves connected by a silver braided flexible hose underneath the boiler).
  2. Open both valves slowly to let mains water into the heating system.
  3. Watch the pressure gauge on the front panel until the needle reaches between 1.0 and 1.5 bar, then firmly close both valves.

Parts commonly replaced

  • Filling loop valve
  • Pressure sensor
  • Expansion vessel

Related codes

Full explanation for E13
F00

Your boiler has temporarily stopped working because it cannot properly read the temperature of the water flowing through it.

High Engineer only £90-180

Parts commonly replaced

  • Flow NTC sensor
  • Wiring harness

Related codes

Full explanation for F00
F04

Your boiler has lost its connection to a temperature sensor on the return pipe, so it has safely shut down to prevent overheating.

High Engineer only £90-180

Parts commonly replaced

  • Return NTC thermistor
  • Wiring harness

Related codes

Full explanation for F04
F05

Your boiler has lost the signal from the sensor that measures hot water temperatures, meaning it cannot properly regulate your taps and showers.

Medium Engineer only £100-200

Parts commonly replaced

  • DHW NTC sensor
  • Wiring harness

Related codes

Full explanation for F05
F10

Your boiler has stopped working because its internal temperature sensor has developed an electrical fault.

High Engineer only £90-180

Parts commonly replaced

  • Flow NTC sensor
  • Wiring harness

Related codes

Full explanation for F10
F14

Your boiler has stopped working because a sensor that measures the temperature of the water returning into the system has developed an electrical fault.

High Engineer only £120-220

Parts commonly replaced

  • Return NTC thermistor
  • Wiring harness

Related codes

Full explanation for F14
F15

Your boiler has detected an electrical fault with the sensor that measures the temperature of your hot water, meaning it cannot properly regulate your hot water supply.

Medium Engineer only £100-200

Parts commonly replaced

  • DHW NTC Sensor
  • Wiring harness

Related codes

Full explanation for F15
F20

Your boiler has automatically shut down because it has become dangerously hot inside.

High Engineer only £150-350

Parts commonly replaced

  • Pump
  • Overheat thermostat
  • NTC thermistor
  • Main heat exchanger

Related codes

Full explanation for F20
Showing 21–26 of 26
F21

Your boiler is failing to ignite because it is not receiving any gas to create a flame for your heating and hot water.

High Engineer only £90-180

Parts commonly replaced

  • Gas valve
  • Ignition lead
  • Electrodes

Related codes

Full explanation for F21
F22

Your boiler has temporarily shut down because the internal water pressure has dropped too low to run safely.

High DIY-safe

What to check first

  1. Locate the filling loop underneath your boiler.
  2. Open the valves gently to let water into the system until the pressure gauge reads between 1.0 and 1.5 bar.
  3. Close the valves tightly and press the reset button on your boiler.

Parts commonly replaced

  • Pressure relief valve
  • Pressure sensor
  • Automatic air vent

Related codes

Full explanation for F22
F23

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

High DIY-safe

What to check first

  1. Locate the filling loop underneath your boiler, which usually consists of a flexible silver hose with one or two small valves.
  2. Slowly open the valves to let mains water into the heating system, keeping an eye on the pressure gauge.
  3. Stop filling once the needle on the pressure gauge reaches the green zone (ideally between 1.0 and 1.5 bar) and firmly close both valves.

Parts commonly replaced

  • Filling loop
  • Pressure sensor
  • Expansion vessel

Related codes

Full explanation for F23
F26

Your boiler is temporarily locking out because it thinks it still detects a flame inside when it should be turned off.

High Engineer only £150-350

Parts commonly replaced

  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for F26
F32

Your boiler has detected a blockage or issue with the airflow through the flue, stopping it from operating safely.

Emergency Engineer only £150-£350

Parts commonly replaced

  • Air pressure switch
  • Fan
  • Flue terminal

Related codes

Full explanation for F32
F40

Your boiler has temporarily lost its electrical power supply or experienced a fluctuation in the mains voltage.

High DIY-safe £90-180

What to check first

  1. Check that the fused spur switch next to the boiler is turned on.
  2. Check your household consumer unit (fuse box) to see if a trip switch has activated.
  3. Try resetting the boiler using its reset button once power is verified.

Parts commonly replaced

  • Main PCB
  • Wiring harness
  • Fuse

Related codes

Full explanation for F40