Lochinvar Domestic Hot Water Priority / Sensor or Valve Issue

Boiler runs but domestic hot water (DHW) is not hot enough or fluctuates in temperature

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Faulty DHW sensor, plate heat exchanger scaled, 3-way diverter valve sticking, incorrect DHW setpoint

How to Fix / Troubleshooting

Safety first: Beware of hot water when working on DHW components.

  • Check DHW setpoint: Verify the DHW temperature setting on the Lochinvar control. Increase slightly if too low, staying within safe limits (typically 120–140°F).
  • Inspect DHW sensor: Locate the DHW tank sensor or aquastat. Ensure it is properly inserted and wired. Replace if readings are erratic.
  • Check 3-way valve operation: On combi or indirect systems, ensure the diverter valve moves fully between CH and DHW positions. Listen for motor operation during DHW calls.
  • Descale plate heat exchanger (professional): If on hard water, the DHW plate exchanger may be scaled and require chemical cleaning by a technician.

Professional help: Complex DHW issues, especially with combi boilers, should be evaluated by a Lochinvar-trained technician.

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Repair Difficulty

Hard 4/5

Required Part

DHW Temperature Sensor
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