BoilerFaultCodes Flame slow to stabilise during start up
Insufficient air supply, incorrect nozzle, low fuel pressure, or insufficient draught
Grant Vortex 15-20 Fault codes & diagnostics
10 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Regular Oil 15-20 kW Discontinued
Replaced by: Vortex Blue
Download the Grant Vortex 15-20 manual
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 →
Severity at a glance
Each cell = one fault code. Hover to identify. 1 High
9 Unrated
Just want the most common Grant Vortex 15-20 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes
All 10 documented codes
Tap any card for details
LED / flash-pattern codes
Digital codes
Boiler operating on overheat thermostat
Faulty boiler thermostat
Boiler will not start
No fuel supply, no electricity supply, or burner failing to start
Burner lock-out Your boiler has detected a temporary issue with the burner and has safely shut itself down to prevent any damage.
Your boiler has detected a temporary issue with the burner and has safely shut itself down to prevent any damage.
What to check first
- Check your oil tank to ensure you have enough fuel and that the supply valve is open
- Wait 60 seconds for the internal control unit to reset
- Gently press the illuminated red reset button located on the burner once
Parts commonly replaced
- Photocell
- Ignition electrodes
- Oil nozzle
- Control box
Burner pulsates
Insufficient air supply, incorrect nozzle, or incorrect fuel pressure
Combustion fumes smell
Faulty cleaning cover seal, burner improperly fitted, flue not sealed, or condensate trap issue
Fumes and puffing during starting
Blocked chimney, insufficient draught, or inadequate air supply
Oil odours
Leak in fuel line connections
Visible smoke from flue or high smoke number
Insufficient air supply, incorrect nozzle, or high fuel pressure
Water temperature low
Undersize nozzle, low fuel pressure, fouled heat exchanger, or faulty thermostat
Status & diagnostic codes 2 operating states & engineer diagnostics
Not faults — these are normal operating states. Tap to expand.
2 operating states & engineer diagnostics
Not faults — these are normal operating states. Tap to expand.
26.0 Diagnostic This is not actually a fault code, but a technical setting displayed on your boiler screen indicating the current maximum heat output capacity of the unit. 36.0 Diagnostic This code is simply a technical indicator confirming that your boiler is currently running at its maximum designed heating capacity.