Grant
Grant Boilers Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
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Airlock
Boiler fires but quickly overheats or shuts down; radiators remain cold at top, pump noisy with rushing water sounds.
Airlock in Primary Heating Circuit
Blocked Flue
Boiler shuts down with flue or combustion safety fault; signs of poor combustion, possible smell of fumes near boiler.
Flue Gas Path Obstruction
Blocked Heat Exchanger
Boiler noisy with kettling sounds, poor heat transfer, frequent overheat trips, but burner appears to run.
Primary Heat Exchanger Fouling
Condensate Fault
Boiler locks out during cold weather, gurgling noises, condensate pipe outside is frozen or blocked.
Condensate Drain Blockage or Freeze
DHW Priority Fault
Boiler heats domestic hot water cylinder but does not supply central heating, even when CH is calling.
Diverter or Motorised Valve Fault (Y-plan/S-plan)
Fan Fault
Boiler indicates a fan or air pressure fault; fan does not start or starts then stops, boiler locks out.
Combustion Fan or Air Pressure Switch Failure
Flame Failure
Boiler attempts to start, fan runs, ignition clicks heard, then shuts down with a flame failure indication on the control panel.
Flame Detection Failure
Frost Protection Active
Boiler runs unexpectedly in cold weather even when heating is off at the programmer.
Frost Thermostat or Frost Protection Circuit Operation
High Pressure
Boiler shows high pressure warning, gauge above 3 bar, pressure relief valve discharging water outside.
System Over-Pressurisation
Ignition Lockout
Boiler repeatedly attempts ignition three times then locks out with an ignition error indication.
Repeated Ignition Failure
Lockout
Boiler will not fire, red lockout light illuminated on the burner control box, no heating or hot water.
Burner Lockout Condition
Low Pressure
Boiler display or control indicates low system pressure; boiler will not fire and pressure gauge reads below 0.5 bar.
System Water Pressure Low
No Flame
Boiler display indicates 'No Flame' or similar, burner does not establish a flame and shuts down.
Ignition or Fuel Delivery Failure
Overheat
Boiler shuts down with an overheat indication, manual reset overheat thermostat has tripped on the front or top of the boiler casing.
Boiler Overheat Thermostat Trip
PCB Fault
Boiler is completely dead or shows random error indications; no response to controls despite correct power supply.
Main Control PCB Failure
Power Supply Fault
Boiler display is blank, no lights or response, but other electrical circuits in the property work.
Local Power or Fuse Failure
Pump Fault
Boiler fires but quickly overheats, flow pipe gets very hot while return stays cool, some radiators cold.
Circulating Pump Failure
Sensor Fault
Boiler display shows a sensor error; boiler may not fire or may cycle rapidly.
NTC Temperature Sensor Failure
Thermostat Fault
Boiler does not respond to temperature changes, runs too hot or not hot enough, or cycles rapidly.
Boiler Thermostat or Control Thermistor Failure
Symptom
Boiler casing feels excessively hot to touch during operation.
Insulation or Casing Seal Failure
Symptom
Boiler emits unusual smells, such as oil fumes or burning odours, especially when firing.
Combustion or Electrical Overheating Issue
Symptom
Boiler frequently cycles on and off, providing inconsistent heating and hot water temperatures.
Short Cycling
Symptom
Boiler frequently goes to lockout during windy conditions, especially with external flue.
Flue Draught or Wind Interference
Symptom
Boiler is excessively noisy with vibration transmitted through pipework and casing.
Mechanical Vibration or Resonance
Symptom
Boiler leaking water from underneath the casing or from pipe joints nearby.
Water Leak from Boiler or Pipework
Symptom
Boiler makes loud banging or knocking noises (kettling) during operation.
Kettling Due to Scale or Sludge
Symptom
Boiler pressure rises significantly when heating is on and drops back when off, with occasional discharge from PRV.
Expansion Vessel Failure
Symptom
Boiler runs but domestic hot water from taps is lukewarm or runs hot then quickly cold.
Insufficient Domestic Hot Water Temperature
Symptom
Boiler runs but some radiators never get hot, even when valves are open.
Poor System Balancing or Blocked Branch
Symptom
Boiler starts then shuts down after a few seconds, repeatedly attempting to fire.
Flame Establishment or Flow Fault
Symptom
Boiler trips the electrical circuit breaker or RCD when attempting to start.
Electrical Short or Earth Leakage
Symptom
Boiler will not start at all, but power is present and display is lit; no burner or fan activity.
No Call for Heat or Internal Interlock
Symptom
Boiler’s burner runs continuously without reaching set temperature, system slow to heat.
Under-Firing or Heat Loss
Symptom
Boiler’s burner starts with a loud bang or puff, sometimes with visible smoke at the flue.
Delayed Ignition
Symptom
Radiators are hot at the top but cold at the bottom, while the boiler appears to run normally.
Sludge Build-Up in Radiators
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| Airlock |
Boiler fires but quickly overheats or shuts down; radiators remain cold at top, pump noisy with rushing water sounds.
|
Airlock in Primary Heating Circuit | View Details |
| Blocked Flue |
Boiler shuts down with flue or combustion safety fault; signs of poor combustion, possible smell of fumes near boiler.
|
Flue Gas Path Obstruction | View Details |
| Blocked Heat Exchanger |
Boiler noisy with kettling sounds, poor heat transfer, frequent overheat trips, but burner appears to run.
|
Primary Heat Exchanger Fouling | View Details |
| Condensate Fault |
Boiler locks out during cold weather, gurgling noises, condensate pipe outside is frozen or blocked.
|
Condensate Drain Blockage or Freeze | View Details |
| DHW Priority Fault |
Boiler heats domestic hot water cylinder but does not supply central heating, even when CH is calling.
|
Diverter or Motorised Valve Fault (Y-plan/S-plan) | View Details |
| Fan Fault |
Boiler indicates a fan or air pressure fault; fan does not start or starts then stops, boiler locks out.
|
Combustion Fan or Air Pressure Switch Failure | View Details |
| Flame Failure |
Boiler attempts to start, fan runs, ignition clicks heard, then shuts down with a flame failure indication on the control panel.
|
Flame Detection Failure | View Details |
| Frost Protection Active |
Boiler runs unexpectedly in cold weather even when heating is off at the programmer.
|
Frost Thermostat or Frost Protection Circuit Operation | View Details |
| High Pressure |
Boiler shows high pressure warning, gauge above 3 bar, pressure relief valve discharging water outside.
|
System Over-Pressurisation | View Details |
| Ignition Lockout |
Boiler repeatedly attempts ignition three times then locks out with an ignition error indication.
|
Repeated Ignition Failure | View Details |
| Lockout |
Boiler will not fire, red lockout light illuminated on the burner control box, no heating or hot water.
|
Burner Lockout Condition | View Details |
| Low Pressure |
Boiler display or control indicates low system pressure; boiler will not fire and pressure gauge reads below 0.5 bar.
|
System Water Pressure Low | View Details |
| No Flame |
Boiler display indicates 'No Flame' or similar, burner does not establish a flame and shuts down.
|
Ignition or Fuel Delivery Failure | View Details |
| Overheat |
Boiler shuts down with an overheat indication, manual reset overheat thermostat has tripped on the front or top of the boiler casing.
|
Boiler Overheat Thermostat Trip | View Details |
| PCB Fault |
Boiler is completely dead or shows random error indications; no response to controls despite correct power supply.
|
Main Control PCB Failure | View Details |
| Power Supply Fault |
Boiler display is blank, no lights or response, but other electrical circuits in the property work.
|
Local Power or Fuse Failure | View Details |
| Pump Fault |
Boiler fires but quickly overheats, flow pipe gets very hot while return stays cool, some radiators cold.
|
Circulating Pump Failure | View Details |
| Sensor Fault |
Boiler display shows a sensor error; boiler may not fire or may cycle rapidly.
|
NTC Temperature Sensor Failure | View Details |
| Thermostat Fault |
Boiler does not respond to temperature changes, runs too hot or not hot enough, or cycles rapidly.
|
Boiler Thermostat or Control Thermistor Failure | View Details |
| – |
Boiler casing feels excessively hot to touch during operation.
|
Insulation or Casing Seal Failure | View Details |
| – |
Boiler emits unusual smells, such as oil fumes or burning odours, especially when firing.
|
Combustion or Electrical Overheating Issue | View Details |
| – |
Boiler frequently cycles on and off, providing inconsistent heating and hot water temperatures.
|
Short Cycling | View Details |
| – |
Boiler frequently goes to lockout during windy conditions, especially with external flue.
|
Flue Draught or Wind Interference | View Details |
| – |
Boiler is excessively noisy with vibration transmitted through pipework and casing.
|
Mechanical Vibration or Resonance | View Details |
| – |
Boiler leaking water from underneath the casing or from pipe joints nearby.
|
Water Leak from Boiler or Pipework | View Details |
| – |
Boiler makes loud banging or knocking noises (kettling) during operation.
|
Kettling Due to Scale or Sludge | View Details |
| – |
Boiler pressure rises significantly when heating is on and drops back when off, with occasional discharge from PRV.
|
Expansion Vessel Failure | View Details |
| – |
Boiler runs but domestic hot water from taps is lukewarm or runs hot then quickly cold.
|
Insufficient Domestic Hot Water Temperature | View Details |
| – |
Boiler runs but some radiators never get hot, even when valves are open.
|
Poor System Balancing or Blocked Branch | View Details |
| – |
Boiler starts then shuts down after a few seconds, repeatedly attempting to fire.
|
Flame Establishment or Flow Fault | View Details |
| – |
Boiler trips the electrical circuit breaker or RCD when attempting to start.
|
Electrical Short or Earth Leakage | View Details |
| – |
Boiler will not start at all, but power is present and display is lit; no burner or fan activity.
|
No Call for Heat or Internal Interlock | View Details |
| – |
Boiler’s burner runs continuously without reaching set temperature, system slow to heat.
|
Under-Firing or Heat Loss | View Details |
| – |
Boiler’s burner starts with a loud bang or puff, sometimes with visible smoke at the flue.
|
Delayed Ignition | View Details |
| – |
Radiators are hot at the top but cold at the bottom, while the boiler appears to run normally.
|
Sludge Build-Up in Radiators | View Details |
No matching codes found
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