Grant Outdoor Combi 90 Mkii Fault codes & diagnostics

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

Combi Oil 26 kW 2004-2009 Discontinued

Replaced by: Vortex Outdoor Combi

Download the Grant Outdoor Combi 90 Mkii manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

The fault code is already on your display

Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →

Fault codes

All 2 documented codes

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Amber neon (on panel)

Your boiler has detected that the water pressure in the system is too low to run safely and has switched itself off to prevent damage.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (a flexible silver hose) usually found under the boiler or near the hot water cylinder.
  2. Open the small black valves slowly until you hear water entering the system.
  3. Watch the pressure gauge and close the valves once the needle reaches between 1 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve
Full explanation for Amber neon (on panel)
Red neon (on panel)

Your boiler has shut itself down because it became too hot, acting as a safety precaution to prevent damage.

High DIY-safe £90-220

What to check first

  1. Locate the reset button on the control panel, which may be hidden behind a small screw-off plastic cap.
  2. Ensure all radiator valves are open and the system pressure is between 1 and 1.5 bar on the gauge.
  3. Press the reset button firmly; if the boiler restarts and runs, monitor it, but call a technician if it happens again.

Parts commonly replaced

  • Overheat Thermostat
  • Circulating Pump
  • System Pressure Sensor
Full explanation for Red neon (on panel)