Verified boiler fault code
Keston 31 Fault Code (Heat 2)
Blocking due to flue overheat.
Safety disclaimer
Fault code summary
- Manufacturer
- Keston
- Fault code
- 31
- Fault type
- Overheating, Flue
- Severity
- blocking
- Reset
- The Heat 2 fault screen shows a Press Reset prompt; do not repeatedly reset an unresolved fault.
- Applicable models
- Keston Heat 2 45, Keston Heat 2 55, Keston Heat 2 45P, Keston Heat 2 55P
Quick answer
Blocking due to flue overheat.
What does this fault code mean?
Blocking due to flue overheat.
Common causes
- Flue overheat.
Symptoms
- The boiler fault screen shows code 31 and a blocking condition.
What can the homeowner safely check?
- Record the code and do not obstruct or dismantle the flue.
Boiler reset information
The Heat 2 fault screen shows a Press Reset prompt; do not repeatedly reset an unresolved fault.
When should I call an engineer?
Contact a suitably qualified heating engineer when the fault persists, the boiler locks out, or the manufacturer instructions do not resolve it. For gas appliance work in the UK, use a Gas Safe registered engineer.
Engineer diagnosis
- Investigate flue temperature, flue thermistor and the flue system.
Applicable boiler models
Related fault codes
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Manufacturer documentation
Keston Heat 2 Installation & Servicing ManualFAULT FINDING MENU: Blocking due to flue overheat — code 31.
Last verified
2026-09-12
Frequently asked questions
What does Keston 31 mean?
Blocking due to flue overheat.
Can I reset a Keston 31 fault?
The Heat 2 fault screen shows a Press Reset prompt; do not repeatedly reset an unresolved fault.