navien combi boiler problems

Navien combi boilers, while efficient and reliable, can face operational issues, particularly in demanding settings like a pub/restaurant. A case in point is a scenario where an old LPG gas boiler, previously servicing a sizable establishment, was replaced with a Navien combi boiler, leading to central heating circulation issues.

Identifying the Problem

  1. Central Heating Circulation Issues:
    • Symptoms: Inadequate heating in radiators, with some remaining cold.
    • Initial Diagnosis: Difficulty in circulating hot water through the system. A potential obstruction to flow.
    • Observations: A newly installed pump heats up significantly, suggesting a lack of water flow. Temperature discrepancies in piping suggest flow problems.
  2. Possible Causes:
    • Faulty Installation: Incorrect routing of pipework during the boiler installation.
    • Pump Issues: Faulty or incorrectly installed pump. The replacement pump might not be adequate for the system’s requirements.
    • Secondary Pump Supply Issue: Electrical supply to the central heating pump might be mislabeled or improperly connected.

Proposed Solutions

  1. Reevaluate Pipework:
    • Inspect the newly installed pipework for proper routing and connections. Ensure that it aligns with the requirements of a combi boiler system.
  2. Pump Inspection and Replacement:
    • Examine the new pump’s capacity and compatibility with the system. Consider replacing it with a pump that matches the system’s requirements.
  3. Expansion Vessel Check:
    • Ensure that the white expansion vessel functions properly. This vessel is crucial for the hot water system’s pressure management.
  4. Boiler Circulation Pump Inspection:
    • Investigate the internal circulation pump of the Navien boiler. It might be responsible for the limited heating in the radiators.
  5. Consultation with Navien:
    • Reach out to Navien for technical support. They might offer insights specific to their boiler models.

Additional Considerations

  • Qualified Technician: Engage with a heating engineer who has experience with commercial installations, especially with Navien combi boilers.
  • System Compatibility: Ensure the entire heating and hot water system is compatible with the combi boiler’s operation.
  • Documentation and Manuals: Refer to the boiler’s manual for specific instructions on pipework and system integration.


The transition to a Navien combi boiler in a commercial setting like a pub/restaurant requires careful consideration of the entire heating system. Circulation issues post-installation suggest a need for a thorough inspection of the pipework, pumps, and the boiler’s internal mechanisms. Professional consultation and adherence to manufacturer guidelines are key to resolving these issues effectively.

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