Verified boiler fault code
Alpha 20 Fault Code (E-Tec 28 and 33)
Flame-sensing fault; false flame detection.
Safety disclaimer
Fault code summary
- Manufacturer
- Alpha
- Fault code
- 20
- Fault type
- Flame detection, Electrical, Safety lockout
- Severity
- high
- Reset
- Not specified
- Applicable models
- E-Tec 28, E-Tec 33
Quick answer
Flame-sensing fault; false flame detection.
What does this fault code mean?
Flame-sensing fault; false flame detection.
Common causes
- Flame detected while the gas valve is not open.
- Flame-sensing electrode/lead, electrical short circuit or PCB fault.
Symptoms
This information was not provided in the verified manufacturer source.
What can the homeowner safely check?
This information was not provided in the verified manufacturer source.
Boiler reset information
Reset information was not provided in the verified manufacturer source. 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
- Assess flame-sensing circuit, wiring and PCB.
Applicable boiler models
Related fault codes
- 01 — E-Tec 28 and 33
Ignition failure; flame not detected during the ignition sequence.
Read fault code - 02 — E-Tec 28 and 33
Overheat boiler lockout.
Read fault code - 03 — E-Tec 28 and 33
High flue temperature.
Read fault code - 04 — E-Tec 28 and 33
Gas-valve electrical connection fault.
Read fault code - 05 — E-Tec 28 and 33
CH flow sensor fault.
Read fault code - 06 — E-Tec 28 and 33
DHW sensor fault.
Read fault code - 08 — E-Tec 28 and 33
Maximum number of resets reached (five).
Read fault code - 10 — E-Tec 28 and 33
Primary system pressure low.
Read fault code
Manufacturer documentation
Alpha E-Tec installation and servicing instructions20 | Flame sensing fault | False flame detection — Flame detected but gas valve is not open | Check flame sensing electrode and lead; electrical short circuit on sensing wires; PCB fault
Last verified
2026-09-12
Frequently asked questions
What does Alpha 20 mean?
Flame-sensing fault; false flame detection.