Baxi E.04.03 Fault Code (Baxi 200/400/600/800 and Assure 500 Combi/System common-code group)

Safety disclaimer

Fault code summary

Manufacturer

Baxi

Fault code

E.04.03

Fault type

Overheating, Temperature sensor, Central heating

Severity

high

Reset

Not specified

Applicable models

Baxi 200 Combi, Baxi 400 Combi, Baxi 600 Combi, Baxi 800 Combi, Baxi Assure 500 Combi, Baxi 600 System, Baxi 800 System, Baxi Assure 500 System

Quick answer

Maximum flow temperature exceeded or flow temperature sensor short-circuited.

What does this fault code mean?

Maximum flow temperature exceeded or flow temperature sensor short-circuited.

Common causes

• Maximum flow temperature exceeded.
• Flow temperature sensor short-circuited.

Symptoms

• The boiler may stop on a high-temperature safety condition.

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 flow temperature, sensor circuit and circulation.

Applicable boiler models

• Baxi 200 Combi
• Baxi 400 Combi
• Baxi 600 Combi
• Baxi 800 Combi
• Baxi Assure 500 Combi
• Baxi 600 System
• Baxi 800 System
• Baxi Assure 500 System

Related fault codes

• A.02.06 — Baxi 200/400/600/800 and Assure 500 Combi/System common-code group

  Low system pressure in the heating circuit.

  Read fault code
• E.00.04 — Baxi 200/400/600/800 and Assure 500 Combi/System common-code group

  Return temperature sensor disconnected.

  Read fault code
• E.01.04 — Baxi 200/400/600/800 and Assure 500 Combi/System common-code group

  Flame loss detected five times in 24 hours.

  Read fault code
• E.01.17 — Baxi 200/400/600/800 and Assure 500 Combi/System common-code group

  No water circulation (permanent).

  Read fault code
• E.04.01 — Baxi 200/400/600/800 and Assure 500 Combi/System common-code group

  Flow temperature sensor short-circuited.

  Read fault code
• E.04.10 — Baxi 200/400/600/800 and Assure 500 Combi/System common-code group

  Burner failed to ignite after four attempts.

  Read fault code
• E.04.12 — Baxi 200/400/600/800 and Assure 500 Combi/System common-code group

  Ignition failure — flame monitoring.

  Read fault code
• E.04.13 — Baxi 200/400/600/800 and Assure 500 Combi/System common-code group

  Fan impeller blocked or maximum RPM exceeded.

  Read fault code

Manufacturer documentation

E.04.03 | Maximum flow temperature exceeded or flow temperature sensor short circuited.

Last verified

2026-09-12

Frequently asked questions