CTC water heater emits a high-pitched whistling or hissing sound when running

Safety first: Use caution around hot water lines; they may be very hot.

Steps to check:

• Verify that the cold water shutoff valve to the heater is fully open.
• Clean the inlet filter screen on the CTC water heater.
• Inspect and flush the thermostatic mixing valve if equipped.
• Check house water pressure; if above manufacturer limits, install or service a pressure reducing valve.