Guide
Boiler Fault Codes: When to Stop and Call a Professional
A UK-focused guide to knowing when a boiler fault has moved beyond safe user checks.
Boiler issues need a more cautious approach than most white goods, especially where gas, combustion, or repeated lockouts are involved.
Last updated: 12 May 2026
Boiler fault codes often indicate pressure, ignition, sensor, or combustion problems. Some user checks are reasonable, but repeated faults should not be treated as a DIY repair project.
Stop and call a professional when
- The boiler repeatedly locks out after a standard user reset.
- You suspect a gas supply, ignition, or combustion issue.
- Pressure drops again quickly after topping up.
- Any step would require opening the boiler casing.
High-priority boiler fault codes
Vaillant Boiler F32
Fan, flue, or air pressure sensing problem
Vaillant Boiler F24
Water circulation or pump performance issue
Vaillant Boiler F25
Overheat protection fault
Vaillant Boiler F27
Flame detection has been lost during operation
Vaillant Boiler F28
The boiler failed during ignition
Vaillant Boiler F29
The boiler lost flame while running
Vaillant Boiler F75
Water circulation or pump performance issue
Ideal Boiler F9
The boiler is not seeing healthy water circulation
Common low-pressure boiler fault codes
Vaillant Boiler F22
The heating system pressure is too low
Vaillant Boiler F23
System water pressure is too low
Baxi Boiler 117
System water pressure is too low
Baxi Boiler 118
System water pressure is too low
Ideal Boiler D4
System water pressure is too low
Ideal Boiler F1
System water pressure is too low
Worcester Bosch Boiler 224
System water pressure is too low
Worcester Bosch Boiler 227
System water pressure is too low
Common ignition and flame-loss boiler codes
Vaillant Boiler F32
Fan, flue, or air pressure sensing problem
Vaillant Boiler F24
Water circulation or pump performance issue
Vaillant Boiler F25
Overheat protection fault
Vaillant Boiler F27
Flame detection has been lost during operation
Vaillant Boiler F28
The boiler failed during ignition
Vaillant Boiler F29
The boiler lost flame while running
Vaillant Boiler F75
Water circulation or pump performance issue
Ideal Boiler F9
The boiler is not seeing healthy water circulation
Vaillant boiler faults needing cautious checks
Vaillant Boiler F32
Fan, flue, or air pressure sensing problem
Vaillant Boiler F24
Water circulation or pump performance issue
Vaillant Boiler F25
Overheat protection fault
Vaillant Boiler F27
Flame detection has been lost during operation
Vaillant Boiler F28
The boiler failed during ignition
Vaillant Boiler F29
The boiler lost flame while running
Vaillant Boiler F75
Water circulation or pump performance issue
Vaillant Boiler F22
The heating system pressure is too low
Baxi boiler faults needing cautious checks
Baxi Boiler E110
the boiler has overheated or reached a high-temperature safety limit.
Baxi Boiler E131
the boiler has locked out after an overheating or high-temperature condition.
Baxi Boiler E160
the boiler has detected a fan or air-pressure related fault.
Baxi Boiler 133
The boiler has locked out after failing to light
Baxi Boiler 125
Water circulation or pump performance issue
Baxi Boiler 128
Flame detection has been lost during operation
Baxi Boiler 130
Fan, flue, or air pressure sensing problem
Baxi Boiler E50
Control board or internal communication fault
Frequently asked questions
Can boiler fault codes usually be fixed at home?+
Only some pressure or user-reset situations are suitable for homeowner checks. Gas and internal boiler faults should be left to a qualified engineer.