Grant Vortex Combi 70 Fault codes & diagnostics

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

CombiOil Oil 21 kW

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9 High
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The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 9 documented codes

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Amber neon

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

High DIY-safe £80-150

What to check first

  1. Locate the external filling loop, which is a flexible silver hose connected to two valves under the boiler.
  2. Gradually open both valves to let water into the system while watching the pressure gauge.
  3. Stop opening the valves once the needle on the pressure gauge reaches the green zone, typically between 1.0 and 1.5 bar, then tightly close both valves.

Parts commonly replaced

  • Filling loop
  • Pressure gauge
  • Pressure relief valve
Full explanation for Amber neon
Amber neon lit

Your boiler has stopped working because the water pressure inside the system has dropped below the required level.

High DIY-safe £0-£120

What to check first

  1. Locate the external filling loop, usually two silver flexible hoses connected to the pipework under the boiler.
  2. Open the valves on the loops slowly until you hear water entering the system.
  3. Watch the pressure gauge on the front of the boiler and close the valves once the needle reaches the green zone, typically between 1 and 1.5 bar.

Parts commonly replaced

  • Pressure relief valve
  • Pressure gauge
  • Expansion vessel
Full explanation for Amber neon lit
Burner Lock-out

Your boiler has stopped working because it failed to light the flame safely, and it now needs a manual reset to try restarting.

High DIY-safe £120-250

What to check first

  1. Check your oil tank is not empty and the fuel supply valve is open.
  2. Wait for the red light on the burner to illuminate, then press and hold the reset button for 3 seconds.
  3. If the boiler tries to start but stops again, do not force repeated resets.

Parts commonly replaced

  • Photocell
  • Ignition electrodes
  • Oil burner nozzle
  • Control box

Related codes

Full explanation for Burner Lock-out
Lock-out

Your boiler has stopped working because it failed to start the heating process, triggering a safety system that keeps the burner turned off.

High Engineer only £150-350

Parts commonly replaced

  • Photocell
  • Ignition transformer
  • Oil nozzle
  • Control box

Related codes

Full explanation for Lock-out
Lock-out reset button is lit

Your boiler has detected a problem with the combustion process and has safely shut itself down to prevent any hazards.

High DIY-safe £120-250

What to check first

  1. Check your external fuel supply level (if oil) to ensure the system is not starved of fuel.
  2. Wait five minutes to allow the system to clear, then firmly press the illuminated reset button once.
  3. If the boiler fails to restart after one attempt, do not repeatedly press the button as this can cause flooding of the combustion chamber.

Parts commonly replaced

  • Photocell
  • Ignition electrodes
  • Oil burner pump
  • Control box
Full explanation for Lock-out reset button is lit
Lock-out reset button lit

Your boiler has stopped working because it failed to ignite, causing a safety mechanism to shut the burner down.

High Engineer only £120-250

Parts commonly replaced

  • Photocell
  • Ignition electrodes
  • Oil nozzle
  • Control box
Full explanation for Lock-out reset button lit
Red neon

Your boiler has detected that it is getting too hot and has automatically shut itself down to prevent damage.

High Engineer only £120-250

Parts commonly replaced

  • Overheat thermostat
  • Central heating pump
  • PCB
Full explanation for Red neon
Red neon light

Your boiler has detected that it is getting too hot and has automatically shut down for safety reasons.

High Engineer only £150-300

Parts commonly replaced

  • Overheat thermostat
  • Central heating pump
  • System filter
Full explanation for Red neon light
Red neon lit

Your boiler has automatically turned off because it detected that the internal water temperature became dangerously high.

High Engineer only £120-250

Parts commonly replaced

  • Overheat thermostat
  • Central heating pump
  • System filter
Full explanation for Red neon lit