Weil-McLain Inconsistent Domestic Hot Water Production

Domestic hot water temperature fluctuates or runs out quickly on combi or indirect systems

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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

Scaled DHW heat exchanger, faulty DHW sensor, mixing valve malfunction, priority settings misconfigured

How to Fix / Troubleshooting

Safety first: Hot water can scald. Do not set DHW temperatures above recommended limits (typically 120°F/49°C).

  • 1. Check DHW setpoint: On the Weil-McLain control, verify the domestic hot water temperature setpoint is appropriate and not set too low.
  • 2. Inspect mixing valve: If a thermostatic mixing valve is installed, ensure it is not stuck or set incorrectly. Exercise the valve by turning through its range.
  • 3. Clean strainers: Some systems have inlet strainers on the cold water supply to the boiler or indirect tank. Clean any debris that may restrict flow.
  • 4. Scale buildup: If the boiler is in a hard water area and has not been descaled, the DHW heat exchanger may be restricted and require professional cleaning.
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Repair Difficulty

Medium 3/5

Required Part

Thermostatic Mixing Valve
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