Ariston Excalibur Fault codes & diagnostics

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

Combi Natural GasLPG 24-30 kW 1994-2000 Discontinued

Replaced by: Microcombi

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.
2 Emergency 6 High 1 Low
Just want the most common Ariston Excalibur faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 9 documented codes

Tap any card for details

Anti-frost device

Your boiler has detected that the water inside is getting too cold and has automatically turned on its internal heater to prevent the pipes from freezing.

Low DIY-safe

What to check first

  1. Ensure the boiler remains plugged in and the power supply is switched on
  2. Check that your gas supply is active so the burner can fire if needed
  3. Open any radiator valves in colder rooms to allow water to circulate freely

Parts commonly replaced

  • NTC temperature sensor
  • Main PCB
Full explanation for Anti-frost device
Ignition Failure

Your boiler is unable to light the gas burner to provide heating or hot water and has shut down for safety.

High DIY-safe £100-280

What to check first

  1. Check if other gas appliances, like a cooker, are working to ensure gas is reaching the property.
  2. Ensure your gas meter has credit if you use a pre-payment meter.
  3. Press the 'Reset' button on the control panel to attempt a restart.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Flame Sensing Electrode
  • Printed Circuit Board (PCB)
Full explanation for Ignition Failure
Insufficient System Pressure

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

High DIY-safe £0-120

What to check first

  1. Locate the flexible silver filling loop underneath or near your boiler.
  2. Slowly open the small tap(s) on the loop to allow water into the system.
  3. Watch the pressure gauge and close the taps firmly once it reaches 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve
Full explanation for Insufficient System Pressure
Overheating

Your boiler has shut down because it has detected that the water inside the system has become dangerously hot.

High DIY-safe £120-350

What to check first

  1. Locate the reset button (usually marked 'R') on the control panel and press it.
  2. Ensure all radiator valves are fully open to allow water to flow freely.
  3. Check that your system pressure is between 1.0 and 1.5 bar on the gauge and top up if necessary.

Parts commonly replaced

  • Circulation Pump
  • Overheat Thermostat
  • Main Heat Exchanger (Descaling)
Full explanation for Overheating
Pressure Gauge J < 0.5 bar

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

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver braided hose with small valves underneath the boiler).
  2. Slowly open both taps/levers on the filling loop to allow water into the system.
  3. Watch the pressure gauge until it reaches between 1.0 and 1.5 bar, then close both taps tightly.

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Pressure sensor
Full explanation for Pressure Gauge J < 0.5 bar
Red L.E.D. D

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

High DIY-safe £120-280

What to check first

  1. Check if other gas appliances in your home (like a hob) are working to ensure gas supply is active.
  2. Check your gas meter to ensure it has credit if you use a prepay meter.
  3. Press the 'Reset' button on the control panel to attempt a restart.

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Ignition lead
  • Printed Circuit Board (PCB)
Full explanation for Red L.E.D. D
Red L.E.D. H

Your boiler has switched itself off because the water inside the heat exchanger has become too hot to operate safely.

High DIY-safe £90-280

What to check first

  1. Wait 20 to 30 minutes for the water temperature to cool down naturally.
  2. Check that your radiator valves are fully open and there is no air trapped in the system.
  3. Press the Reset button once the unit has cooled to see if the error clears. If it recurs immediately, call an engineer.

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Main Heat Exchanger
  • Temperature Sensor (NTC)

Related codes

Full explanation for Red L.E.D. H
Yellow L.E.D. "E"

Your boiler has temporarily switched itself off because it has detected a problem with how it is getting rid of waste gases.

Emergency Engineer only £100-280

Parts commonly replaced

  • Flue pressure switch
  • Fan assembly
  • Venturi tube
Full explanation for Yellow L.E.D. "E"
Yellow L.E.D. E

Your boiler has temporarily stopped working because it has detected that dangerous exhaust fumes are not being cleared away safely.

Emergency Engineer only £120-350

Parts commonly replaced

  • Flue Fan
  • Air Pressure Switch
  • Venturi Tube
  • Flue Hood
Full explanation for Yellow L.E.D. E