ATAG 303 Fault Code (i-Range (2019 and newer))

Safety disclaimer

Fault code summary

Manufacturer

ATAG

Fault code

303

Fault type

PCB/electronics

Severity

lockout

Reset

ATAG distinguishes blocking codes from error codes; a locked boiler may require reset and/or service intervention.

Applicable models

ATAG iC, ATAG iS, ATAG iR

Quick answer

PCB fault.

What does this fault code mean?

PCB fault.

Common causes

• PCB fault.

Symptoms

• The ATAG display shows error code 303.

What can the homeowner safely check?

• Record the code and contact the installer.

Boiler reset information

ATAG distinguishes blocking codes from error codes; a locked boiler may require reset and/or service intervention.

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

• Investigate PCB operation and connected circuits.

Applicable boiler models

• ATAG iC
• ATAG iS
• ATAG iR

Related fault codes

• 101 — i-Range (2019 and newer)

  Overheat.

  Read fault code
• 102 — i-Range (2019 and newer)

  Pressure sensor error.

  Read fault code
• 103 — i-Range (2019 and newer)

  Flow check failed three times (flow-check sequence 1, 3 or 4; last check 1).

  Read fault code
• 104 — i-Range (2019 and newer)

  Flow check failed.

  Read fault code
• 105 — i-Range (2019 and newer)

  Flow check failed three times (flow-check sequence 1, 3 or 4; last check 3).

  Read fault code
• 106 — i-Range (2019 and newer)

  Flow check failed three times (flow-check sequence 1, 3 or 4; last check 4).

  Read fault code
• 107 — i-Range (2019 and newer)

  Flow check 5 failed.

  Read fault code
• 108 — i-Range (2019 and newer)

  Pressure below Pmin (less than 0.5 bar); filling is needed.

  Read fault code

Manufacturer documentation

2019 & newer range: 303 — PCB Fault.

Last verified

2026-09-12

Frequently asked questions