De Dietrich Flow Restriction or Gas Flow Noise

Water heater emits a whistling or high-pitched noise when running

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Possible Causes

Partially closed isolation valve on De Dietrich unit, Blocked inlet filter, Gas valve whistling at certain modulation, Air in system

How to Fix / Troubleshooting

Safety first: Distinguish between water and gas noises; gas-related noises must be checked by a professional.

Step-by-step checks:

  • Check valves: Ensure all water isolation valves are fully open.
  • Clean filters: Remove and clean inlet filters to restore full flow.
  • Bleed air: Remove air from radiators and high points.

When to call a professional: If the noise appears to come from the gas valve or burner, contact a gas-safe technician.

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Repair Difficulty

Easy 2/5

Required Part

Inlet Filter
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