Grant boiler error codes help you identify issues in your oil heating system. The most common ones include no flame detection (E01), safety thermostat trips (E02), flue problems (E03), and burner lockout (E05). These codes provide valuable guidance for UK homeowners and landlords.
Grant Boiler Error Codes: A Quick Overview
Grant boiler error codes give clear signals about faults in your oil boiler. Here is a comprehensive table with the full list of common error codes and their meanings.
| Error Code | Meaning |
| E01 | No flame detected during startup |
| E02 | Safety thermostat tripped |
| E03 | Flue thermofuse or temperature issue |
| E05 | Burner lockout |
| E06 | Low water pressure or flow |
| E07 | Overheat condition |
| E08 | Low oil supply or filter issue |
| E09 | Control board or communication fault |
Grant Boiler Error Codes: Causes & How to Fix
Grant boiler error codes cover the typical problems that can occur in oil fired heating systems and understanding them helps you take the right steps. We explain each major code with practical details below.
E01 No Flame Detected During Startup
E01 on your Grant boiler means the burner tried to ignite but could not establish a flame. This safety feature stops unburned oil from building up.
Causes
Low oil in the tank, a blocked oil filter, air in the supply line after a delivery, dirty ignition electrodes, or a faulty nozzle are common causes. Problems with the oil pump or incorrect control settings can also prevent the burner from lighting properly.
How to Fix
- Check the oil tank gauge or use a dipstick to confirm there is enough oil and ensure the supply valve on the line is fully open.
- Locate the reset button on the burner control box and press it once to attempt a restart, listening for the burner fan and ignition sequence.
- A qualified OFTEC registered engineer will isolate the oil supply, remove the oil filter for cleaning or replacement, and inspect the burner nozzle for carbon deposits or wear, replacing it if necessary.
- The oil supply line will be carefully bled using a suitable container to catch oil and remove any air pockets that may have entered the system.
- The ignition electrodes will be removed, cleaned with fine emery cloth or replaced, the spark gap set precisely to the manufacturer’s specification, and the burner reassembled and tested through multiple firing cycles while monitoring flame stability and combustion readings.
E02 Safety Thermostat Tripped
E02 indicates the safety thermostat has activated because water temperatures have risen too high. This protects the boiler from potential damage.
Causes
Restricted water circulation due to closed valves or sludge in the pipes, a weak or failing circulating pump, or scale buildup inside the heat exchanger can cause overheating. A faulty safety thermostat or temperature sensor may also trip incorrectly.
How to Fix
- Check that all radiator valves and any isolation valves on the flow and return pipes are fully open.
- Starting from the highest point in the house, bleed each radiator using a radiator key until water flows steadily without air hissing, collecting water in a cloth or container.
- An OFTEC registered engineer will test the circulating pump for correct operation and either free a seized impeller or replace the entire pump unit.
- The complete heating system will be power flushed with specialist chemicals to remove sludge and scale from pipes, radiators, and the heat exchanger.
- The safety thermostat will be tested with a multimeter, replaced if faulty, and the boiler will be refilled, bled, reset, and run for an extended period while the engineer monitors water temperatures at various points.
If your Grant boiler shows repeated error codes, it may be time to consider a modern replacement. At Eazy Heat we help many customers with new boiler installations that offer better efficiency and fewer faults.
E03 Flue Thermofuse or Temperature Issue
E03 signals a problem with the flue temperature or the safety fuse in the flue system.
Causes
A blocked or damaged flue pipe, excessive soot buildup from poor combustion, or a faulty thermofuse can trigger this code. Dirty burner components or incorrect combustion settings often lead to higher than normal flue temperatures.
How to Fix
- The boiler is safely isolated from power and oil supply.
- An OFTEC registered engineer will inspect the flue terminal outside for blockages and clean the internal flueways and burner assembly to remove soot.
- The flue thermofuse will be tested for continuity and replaced if it has tripped.
- Burner combustion settings will be checked and adjusted using specialist equipment to ensure efficient and clean burning.
- Full safety tests including flue gas analysis will be carried out and the boiler will be reset and monitored over several operating cycles.
E05 Burner Lockout
E05 means the burner has locked out after repeated failed attempts to ignite.
Causes
Blocked oil filters, air in the oil supply line, faulty ignition electrodes, or low oil pressure from the pump are typical causes. A dirty burner nozzle or incorrect electrode gap can also prevent successful firing.
How to Fix
- Check the oil tank level and reset the burner lockout button once.
- An OFTEC registered engineer will clean or replace the oil filter and inspect the burner nozzle for wear.
- The oil pump pressure will be measured with a gauge and adjusted or the pump replaced if necessary.
- Ignition electrodes will be removed, cleaned or replaced, and the spark gap set precisely using a feeler gauge.
- The burner will be reassembled and tested through multiple firing cycles while the engineer monitors flame stability, smoke levels, and CO2 readings with combustion analysis equipment.
E06 Low Water Pressure or Flow Issue
E06 indicates that water pressure or circulation in the heating system is insufficient.
Causes
Leaks in pipes or radiators, a weak circulating pump, air locks in the system, or sludge buildup restricting flow are common reasons. Larger systems with many radiators are particularly prone to flow problems if not maintained.
How to Fix
- Check the system pressure gauge and top up using the filling loop until it reaches 1 to 1.5 bar.
- Bleed all radiators starting from the highest point in the house.
- An OFTEC registered engineer will test the circulating pump and replace it if it is not delivering adequate flow.
- The entire heating system will be power flushed with chemicals to remove sludge from pipes and radiators.
- The system will be refilled, bled again, and the boiler will be run through extended heating cycles while the engineer monitors pressure, flow rates, and temperatures.
E07 Overheat Condition
E07 shows the boiler has detected excessively high temperatures and has shut down for safety.
Causes
Poor water circulation from closed valves or blockages, a failing pump, or scale buildup in the heat exchanger can cause overheating. A faulty temperature sensor may also give incorrect high readings.
How to Fix
- Ensure all radiator valves are fully open.
- Bleed the system to remove air.
- An OFTEC registered engineer will flush the heat exchanger and check circulation.
- Temperature sensors and the safety thermostat will be tested and replaced if faulty.
- The system will be refilled, reset, and run while temperatures are closely monitored.
E08 Low Oil Supply or Filter Issue
E08 signals that oil is not reaching the burner properly.
Causes
Low oil in the tank, blocked filters, kinked supply lines, or a failing oil pump interrupt delivery. Air leaks in the line can cause intermittent faults.
How to Fix
- Refill the oil tank if low.
- An OFTEC registered engineer will clean or replace the oil filter.
- The supply line will be inspected for kinks and bled to remove air.
- The oil pump will be tested for correct pressure.
- Burner operation will be verified with multiple test firings.
E09 Control Board or Communication Fault
E09 points to a problem with the main control board or signals between components.
Causes
Electrical surges, age related board failure, loose connections, or corrosion from moisture can cause this.
How to Fix
- The boiler is isolated.
- An engineer checks all connections and the control board.
- Faulty boards are replaced.
- Electrical supply is tested for stability.
- The system is reprogrammed and fully tested.
Get a New Boiler and Save On Costly Repair Bills
Frequent grant boiler error codes can become expensive. Many UK homeowners choose new boiler installations for improved reliability.
At Eazy Heat, we provide expert new boiler installations for homeowners and landlords across the UK. Contact us today for a free online new boiler quote. Let us help you enjoy dependable heating without the worry of frequent faults. Your comfort is our priority.
FAQs
How often should Grant oil boilers be serviced?
Annual servicing by an OFTEC registered engineer is essential to prevent error codes.
Can I reset Grant error codes myself?
Simple resets are okay, but repeated faults require professional attention.
Are Grant boilers suitable for larger properties?
Yes, when correctly sized they provide reliable heating for bigger homes.
What should landlords do when error codes appear?
Arrange prompt repairs to maintain tenant comfort and legal compliance.
Do newer oil boilers have fewer error codes?
Modern designs often include better components and diagnostics for greater reliability.