Vaillant F.64 Fault Code (ecoTEC plus/pro (manual models))

Safety disclaimer

Fault code summary

Manufacturer

Vaillant

Fault code

F.64

Fault type

PCB/electronics, Temperature sensor

Severity

Not specified

Reset

Not specified

Applicable models

ecoTEC plus 612, ecoTEC plus 615, ecoTEC plus 618, ecoTEC plus 624, ecoTEC plus 630, ecoTEC plus 637, ecoTEC plus 824, ecoTEC plus 831, ecoTEC plus 837, ecoTEC pro 28

Quick answer

Electronics/NTC fault.

What does this fault code mean?

Electronics/NTC fault.

Common causes

• Short circuit in flow or return NTC.
• Electronics defective.

Symptoms

This information was not provided in the verified manufacturer source.

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/return NTC circuits and the appliance electronics.

Applicable boiler models

• ecoTEC plus 612
• ecoTEC plus 615
• ecoTEC plus 618
• ecoTEC plus 624
• ecoTEC plus 630
• ecoTEC plus 637
• ecoTEC plus 824
• ecoTEC plus 831
• ecoTEC plus 837
• ecoTEC pro 28

Related fault codes

• F.22 — ecoTEC plus/pro (manual models)

  Dry fire.

  Read fault code
• F.23 — ecoTEC plus/pro (manual models)

  Water shortage; the temperature difference between flow and return NTC is too large.

  Read fault code
• F.24 — ecoTEC plus/pro (manual models)

  Water shortage; temperature rise too quick.

  Read fault code
• F.25 — ecoTEC plus/pro (manual models)

  Interruption in the compact thermal module cable harness.

  Read fault code
• F.28 — ecoTEC plus/pro (manual models)

  The appliance does not start: attempts to ignite during start failed.

  Read fault code
• F.29 — ecoTEC plus/pro (manual models)

  The flame goes off during operation and subsequent ignition attempts fail.

  Read fault code
• F.32 — ecoTEC plus/pro (manual models)

  Fan speed variation.

  Read fault code
• F.49 — ecoTEC plus/pro (manual models)

  eBUS undervoltage.

  Read fault code

Manufacturer documentation

F.64 | Electronics/NTC fault | Short-circuit in flow or return NTC or electronics defective

Last verified

2026-09-12

Frequently asked questions