Grant
Grant Boilers Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
Advertisements
Airlock
The boiler fires but quickly overheats or shuts down; radiators remain cold at the top, and the pump is noisy with rushing water sounds.
Airlock in Primary Heating Circuit
Blocked Flue
The boiler shuts down with a flue or combustion safety fault; there are signs of poor combustion, and a possible smell of fumes near the boiler.
Flue Gas Path Obstruction
Blocked Heat Exchanger
The boiler is noisy with kettling sounds, exhibits poor heat transfer, and experiences frequent overheat trips, but the burner appears to run.
Primary Heat Exchanger Fouling
Condensate Fault
The boiler locks out during cold weather, gurgling noises are heard, and the condensate pipe outside is frozen or blocked.
Condensate Drain Blockage or Freeze
DHW Priority Fault
The boiler heats the domestic hot water cylinder but does not supply central heating, even when central heating is calling.
Diverter or Motorised Valve Fault (Y-plan/S-plan)
Fan Fault
The boiler indicates a fan or air pressure fault; the fan does not start or starts then stops, and the 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
The 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
The 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; the 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
The boiler is completely dead or shows random error indications; there is no response to controls despite a correct power supply.
Main Control PCB Failure
Power Supply Fault
The boiler display is blank, with no lights or response, but other electrical circuits in the property are working.
Local Power or Fuse Failure
Pump Fault
The boiler fires but quickly overheats; the flow pipe gets very hot while the return pipe stays cool, and some radiators remain cold.
Circulating Pump Failure
Sensor Fault
The boiler display shows a sensor error; the boiler may not fire or may cycle rapidly.
NTC Temperature Sensor Failure
Thermostat Fault
The 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 frequently goes to lockout during windy conditions, especially with an external flue.
Flue Draft or Wind Interference
Symptom
Boiler is excessively noisy with vibration transmitted through pipework and casing.
Mechanical Vibration or Resonance
Symptom
Boiler pressure rises significantly when heating is on and drops back when off, with occasional discharge from the PRV.
Expansion Vessel Failure
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 the display is lit; no burner or fan activity.
No Call for Heat or Internal Interlock
Symptom
Boiler's burner runs continuously without reaching the set temperature; the system is 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
Symptom
The boiler emits unusual smells, such as oil fumes or burning odours, especially when firing.
Combustion or Electrical Overheating Issue
Symptom
The boiler frequently cycles on and off, providing inconsistent heating and hot water temperatures.
Short Cycling
Symptom
The boiler is leaking water from underneath its casing or from nearby pipe joints.
Water Leak from Boiler or Pipework
Symptom
The boiler makes loud banging or knocking noises (kettling) during operation.
Kettling Due to Scale or Sludge
Symptom
The boiler runs, but domestic hot water from the taps is lukewarm or runs hot then quickly cold.
Insufficient Domestic Hot Water Temperature
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| Airlock |
The boiler fires but quickly overheats or shuts down; radiators remain cold at the top, and the pump is noisy with rushing water sounds.
|
Airlock in Primary Heating Circuit | View Details |
| Blocked Flue |
The boiler shuts down with a flue or combustion safety fault; there are signs of poor combustion, and a possible smell of fumes near the boiler.
|
Flue Gas Path Obstruction | View Details |
| Blocked Heat Exchanger |
The boiler is noisy with kettling sounds, exhibits poor heat transfer, and experiences frequent overheat trips, but the burner appears to run.
|
Primary Heat Exchanger Fouling | View Details |
| Condensate Fault |
The boiler locks out during cold weather, gurgling noises are heard, and the condensate pipe outside is frozen or blocked.
|
Condensate Drain Blockage or Freeze | View Details |
| DHW Priority Fault |
The boiler heats the domestic hot water cylinder but does not supply central heating, even when central heating is calling.
|
Diverter or Motorised Valve Fault (Y-plan/S-plan) | View Details |
| Fan Fault |
The boiler indicates a fan or air pressure fault; the fan does not start or starts then stops, and the 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 |
The 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 |
The 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; the 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 |
The boiler is completely dead or shows random error indications; there is no response to controls despite a correct power supply.
|
Main Control PCB Failure | View Details |
| Power Supply Fault |
The boiler display is blank, with no lights or response, but other electrical circuits in the property are working.
|
Local Power or Fuse Failure | View Details |
| Pump Fault |
The boiler fires but quickly overheats; the flow pipe gets very hot while the return pipe stays cool, and some radiators remain cold.
|
Circulating Pump Failure | View Details |
| Sensor Fault |
The boiler display shows a sensor error; the boiler may not fire or may cycle rapidly.
|
NTC Temperature Sensor Failure | View Details |
| Thermostat Fault |
The 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 frequently goes to lockout during windy conditions, especially with an external flue.
|
Flue Draft or Wind Interference | View Details |
| – |
Boiler is excessively noisy with vibration transmitted through pipework and casing.
|
Mechanical Vibration or Resonance | View Details |
| – |
Boiler pressure rises significantly when heating is on and drops back when off, with occasional discharge from the PRV.
|
Expansion Vessel Failure | 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 the display is lit; no burner or fan activity.
|
No Call for Heat or Internal Interlock | View Details |
| – |
Boiler's burner runs continuously without reaching the set temperature; the system is 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 |
| – |
The boiler emits unusual smells, such as oil fumes or burning odours, especially when firing.
|
Combustion or Electrical Overheating Issue | View Details |
| – |
The boiler frequently cycles on and off, providing inconsistent heating and hot water temperatures.
|
Short Cycling | View Details |
| – |
The boiler is leaking water from underneath its casing or from nearby pipe joints.
|
Water Leak from Boiler or Pipework | View Details |
| – |
The boiler makes loud banging or knocking noises (kettling) during operation.
|
Kettling Due to Scale or Sludge | View Details |
| – |
The boiler runs, but domestic hot water from the taps is lukewarm or runs hot then quickly cold.
|
Insufficient Domestic Hot Water Temperature | View Details |
No matching codes found
Advertisements