Error code
Ideal Boiler Fault Code F4
The boiler has failed to ignite on demand The most likely cause is gas supply interruption or meter problem. Check first: check the thermostat, programmer, and any user controls are calling for heat.
Quick answer
F4: what does it mean and how to fix
What does it mean?
The boiler has failed to ignite on demand
How to fix first
Check whether other gas appliances appear to have supply, without opening the boiler.
Why is this happening?
Gas supply interruption or meter problem
When should I call an engineer?
Call a Gas Safe registered engineer if F4 returns after one reset, other gas appliances work normally, or the boiler repeatedly attempts ignition without lighting.
What does this error code mean?
Ideal boiler fault code F4 usually means the boiler has not established a flame when it tried to start. It is an ignition fault, so user checks should stay outside the boiler and focus on supply, controls, and a single permitted reset.
This code sits in the ignition path, including gas supply, condensate condition, ignition electrode, flame sensing, gas valve, fan, flue, and controls.
Start with this safe check: Check whether other gas appliances appear to have supply, without opening the boiler. If the code returns, the fault worsens, or the appliance does not behave normally, call a Gas Safe registered engineer if F4 returns after one reset, other gas appliances work normally, or the boiler repeatedly attempts ignition without lighting.
Symptoms users may notice
- The boiler may fail before radiators or hot water warm up.
- You may hear the boiler try to start and then lock out.
- The display may show F4 after a heating or hot water demand.
What users often notice
- F4 is usually noticed when there is demand for heat but the boiler does not complete the lighting sequence.
Why is this happening?
- Gas supply interruption or meter problem
- Ignition electrode or flame sensing issue
- Condensate pipe blockage on suitable condensing models in cold weather
- Gas valve, fan, flue, or PCB issue requiring qualified diagnosis
What this usually points to
This code sits in the ignition path, including gas supply, condensate condition, ignition electrode, flame sensing, gas valve, fan, flue, and controls.
How to fix this safely
- Check whether other gas appliances appear to have supply, without opening the boiler.
- Check the thermostat, programmer, and any user controls are calling for heat.
- Use one standard reset only if the Ideal manual allows it.
- Do not remove the casing or attempt to clean ignition parts.
What not to do
- Do not repeatedly reset the boiler.
- Do not open the casing or interfere with ignition, gas, or combustion parts.
Common misdiagnoses
- F4 can be mistaken for a thermostat problem, but the code usually points to ignition or flame proving inside the boiler.
Reset steps
- Follow the reset instructions shown on the boiler control panel or in the manual.
- Allow the boiler one attempt to fire.
- If F4 reappears, book a Gas Safe registered engineer.
Intermittent vs persistent faults
A one-off F4 after a gas supply issue may clear with one permitted reset; repeated F4 needs professional diagnosis.
When to call an engineer
Call a Gas Safe registered engineer if F4 returns after one reset, other gas appliances work normally, or the boiler repeatedly attempts ignition without lighting.
Safety warning
Do not remove the boiler casing or try to work on gas, ignition, or combustion components yourself.
Useful hub links
Related ignition fault codes
Relevant guide
Frequently asked questions
Can I keep resetting an Ideal boiler with F4?+
No. One permitted reset is enough. Repeated resets do not repair an ignition fault.
Is Ideal F4 the same as L2?+
They are related ignition or flame-proving faults on many Ideal ranges, but the exact meaning can vary by model, so use the manual for your boiler.
Can a thermostat cause F4?+
A thermostat issue can stop demand, but F4 normally means the boiler received demand and then failed during ignition.
Can I check the electrode myself?+
No. Electrode and flame sensing checks require opening the boiler and must be left to a Gas Safe registered engineer.