Navien NCB-20LHWE Fault codes & diagnostics

1 fault code with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Gas 2014-present
GC Number 41-709-01
Download the Navien NCB-20LHWE manualThe official installation and service manual (PDF), the document these fault codes were read from. PDF

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Versions & GC numbers

Which version do you have?

The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.

GC number Appliance (register name) Produced
41-709-01 NCB-20LHWE 2014–present

Appliance names and production years are taken from the UK Product Characteristics Database (the SAP/SEDBUK register). Where a GC number is also printed in this model's own manufacturer manual, both sources were checked to agree.

Fault codes

All 1 documented codes

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E02

Your boiler has temporarily stopped working because the water pressure inside the system has dropped too low.

High DIY-safe

What to check first

  1. Locate the filling loop valves underneath your boiler.
  2. Open the valves gently to allow water into the system until the pressure gauge reads between 1 and 1.5 bar.
  3. Close both valves firmly and check the gauge holds steady, then reset the boiler.

Parts commonly replaced

  • Pressure sensor
  • Filling loop

Related codes

Full explanation for E02
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