Grant Vortex Pro 15-26 Fault codes & diagnostics

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

Oil 15-26 kW 2008-present
Download the Grant Vortex Pro 15-26 manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

This boiler uses LED flash patterns

Count the flashes in one repeating group before the pause. That number is your fault code. Do not reset until you have noted it. How to read fault codes →

Just want the most common Grant Vortex Pro 15-26 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 5 documented codes

Tap any card for details

LED / flash-pattern codes
Flashes red

Your boiler has stopped heating because the internal water pump, which moves hot water around your house, has seized up or failed and cannot restart itself.

High Engineer only £250-450

Parts commonly replaced

  • Circulator pump
  • Pump capacitor
  • Wiring harness
Full explanation for Flashes red
Flashes red/green

Your boiler is struggling because the internal water pump is stuck or not receiving power, which prevents heat from circulating through your home.

High Engineer only £150-300

Parts commonly replaced

  • Central heating pump
  • Pump electrical cable
  • PCB
Full explanation for Flashes red/green
Digital codes
LED off

Your boiler has completely lost power and is unable to turn on, meaning it cannot provide any heating or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Fuse
  • Control board
  • Power supply cable
Full explanation for LED off
Status & diagnostic codes

4 operating states & engineer diagnostics

Not faults — these are normal operating states. Tap to expand.

21.0 Diagnostic This code indicates that the boiler is currently operating at its maximum heating capacity and is not necessarily a sign of a fault or breakdown. 26.0 Diagnostic Your boiler is currently operating at its highest possible power setting to meet the heat demand requested by your thermostat. 36.0 Diagnostic This code is simply displaying the current maximum power setting of your boiler and is not an error message indicating a fault. A1.2 Diagnostic Your boiler is currently running normally and is successfully performing its routine heating cycle.
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