Verified boiler fault code

Keston 99 Fault Code (Heat 2)

System lockout caused by an internal lockout error.

Safety disclaimer

Boiler repair help from Aza & Sons Services

Fault code summary

Manufacturer
Keston
Fault code
99
Fault type
PCB/electronics, Safety lockout
Severity
lockout
Reset
Not specified
Applicable models
Keston Heat 2 45, Keston Heat 2 55, Keston Heat 2 45P, Keston Heat 2 55P

Quick answer

System lockout caused by an internal lockout error.

What does this fault code mean?

System lockout caused by an internal lockout error.

Common causes

  • Internal system lockout error.

Symptoms

  • The boiler fault screen shows code 99 and a system lockout.

What can the homeowner safely check?

  • Record the code and contact the service provider.

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

  • Review internal fault history and controller electronics.

Applicable boiler models

Related fault codes

Manufacturer documentation

Keston Heat 2 Installation & Servicing Manual

FAULT FINDING MENU (continued): System lockout (internal lockout error) — code 99.

Last verified

2026-09-12

Frequently asked questions

What does Keston 99 mean?

System lockout caused by an internal lockout error.