Potterton E12 Fault Code (Assure Combi & System)

Safety disclaimer

Fault code summary

Manufacturer

Potterton

Fault code

E12

Fault type

Flow sensor, Circulation

Severity

Not specified

Reset

Not specified

Applicable models

Potterton Assure Combi, Potterton Assure System

Quick answer

Differential water-flow switch fault; the switch is still open.

What does this fault code mean?

Differential water-flow switch fault; the switch is still open.

Common causes

• Differential water flow switch still open.

Symptoms

• The boiler displays E12 and may stop operating.

What can the homeowner safely check?

• Note the code and consult the Potterton instructions.

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

• Check the differential flow switch and the primary circuit.

Applicable boiler models

• Potterton Assure Combi
• Potterton Assure System

Related fault codes

• E09 — Assure Combi & System

  Gas valve connection fault.

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• E10 — Assure Combi & System

  External probe fault.

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• E109 — Assure Combi & System

  Precirculation alarm.

  Read fault code
• E110 — Assure Combi & System

  The boiler maximum temperature was exceeded, or the safety thermostat sensor tripped.

  Read fault code
• E118 — Assure Combi & System

  Water pressure is low, below 0.5 bar.

  Read fault code
• E125 — Assure Combi & System

  Water circulation fault.

  Read fault code
• E128 — Assure Combi & System

  Safety error for frequent loss of flame.

  Read fault code
• E129 — Assure Combi & System

  Safety error for frequent loss of flame with maximum correction during ignition calibration.

  Read fault code

Manufacturer documentation

Potterton Assure Combi & System — E12: Differential water flow switch fault (still open).

Last verified

2026-09-12

Frequently asked questions