Warmflow E15 Fault Code (Agentis Boilers (B-Series, I-Series and E-Series))

Safety disclaimer

Fault code summary

Manufacturer

Warmflow

Fault code

E15

Fault type

Temperature sensor, Central heating

Severity

medium

Reset

The manual states that E15 is stored in error history for diagnosis and is not displayed on the LCD; no user reset is confirmed.

Applicable models

B21, B26, B33, I21, I26, I33, I44, I21PRO, I26PRO, I33PRO, I44PRO, I21P/PRO, I26P/PRO, I33P/PRO, I44P, I21S/PRO, I26S/PRO, I33S/PRO, I21C/PRO, I26C/PRO, I33C/PRO, E21, E26, E33, E44, E21PRO, E26PRO, E33PRO, E44PRO, E21P/PRO, E26P/PRO, E33P/PRO, E44P, E21S/PRO, E26S/PRO, E33S/PRO, E21C/PRO, E26C/PRO, E33C/PRO

Quick answer

CH return NTC error.

What does this fault code mean?

CH return NTC error.

Common causes

• CH-return NTC temperature sensor short circuit or disconnection

Symptoms

• E15 stored in the error history; it is not displayed on the LCD

What can the homeowner safely check?

• Record any stored code and arrange qualified service; do not access the sensor.

Boiler reset information

The manual states that E15 is stored in error history for diagnosis and is not displayed on the LCD; no user reset is confirmed.

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

• A qualified engineer should inspect the CH-return NTC sensor, wiring and control board.

Applicable boiler models

• B21
• B26
• B33
• I21
• I26
• I33
• I44
• I21PRO
• I26PRO
• I33PRO
• I44PRO
• I21P/PRO
• I26P/PRO
• I33P/PRO
• I44P
• I21S/PRO
• I26S/PRO
• I33S/PRO
• I21C/PRO
• I26C/PRO
• I33C/PRO
• E21
• E26
• E33
• E44
• E21PRO
• E26PRO
• E33PRO
• E44PRO
• E21P/PRO
• E26P/PRO
• E33P/PRO
• E44P
• E21S/PRO
• E26S/PRO
• E33S/PRO
• E21C/PRO
• E26C/PRO
• E33C/PRO

Related fault codes

• E01 — Agentis Boilers (B-Series, I-Series and E-Series)

  Burner lockout.

  Read fault code
• E02 — Agentis Boilers (B-Series, I-Series and E-Series)

  High limit.

  Read fault code
• E05 — Agentis Boilers (B-Series, I-Series and E-Series)

  Boiler NTC error.

  Read fault code
• E06 — Agentis Boilers (B-Series, I-Series and E-Series)

  DHW flow NTC error.

  Read fault code
• E11 — Agentis Boilers (B-Series, I-Series and E-Series)

  Tank limit.

  Read fault code
• E12 — Agentis Boilers (B-Series, I-Series and E-Series)

  Tank-control NTC error.

  Read fault code
• E22 — Agentis Boilers (B-Series, I-Series and E-Series)

  Flash data corrupted.

  Read fault code
• E31 — Agentis Boilers (B-Series, I-Series and E-Series)

  Remote-control communication error.

  Read fault code

Manufacturer documentation

Error codes displayed on the LCD: | E15* | CH Return NTC Error | CH Return NTC Temperature Sensor short circuit or disconnected | Consult Service Engineer | *Error Codes E11, E15 are not displayed on the LCD, and are only stored in the Error History for diagnosis.

Last verified

2026-09-12

Frequently asked questions