Alpha 20 Fault Code (Evoke 28 and 33)

Safety disclaimer

Fault code summary

Manufacturer

Alpha

Fault code

20

Fault type

Flame detection, Electrical, Safety lockout

Severity

high

Reset

Not specified

Applicable models

Evoke 28, Evoke 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

• Evoke 28
• Evoke 33

Related fault codes

• 01 — Evoke 28 and 33

  Ignition failure; flame not detected during the ignition sequence.

  Read fault code
• 02 — Evoke 28 and 33

  Overheat boiler lockout.

  Read fault code
• 03 — Evoke 28 and 33

  High flue temperature.

  Read fault code
• 04 — Evoke 28 and 33

  Gas-valve electrical connection fault.

  Read fault code
• 05 — Evoke 28 and 33

  CH flow sensor fault.

  Read fault code
• 06 — Evoke 28 and 33

  DHW sensor fault.

  Read fault code
• 08 — Evoke 28 and 33

  Maximum number of resets reached (five).

  Read fault code
• 10 — Evoke 28 and 33

  Primary system pressure low.

  Read fault code

Manufacturer documentation

20 | 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