How to Fix / Troubleshooting

Safety first: Water may become very hot unexpectedly; use caution when testing.

Steps to check and correct:

Increase flow: Fully open the hot side at the shower and reduce cold mixing to ensure flow through the Noritz unit stays above minimum.
Clean fixtures: Remove and clean showerheads and faucet aerators to restore full flow.
Check mixing valves: If you have anti-scald or thermostatic valves, they may be overcompensating. Adjust or have them serviced.
Descale unit: Perform a descaling flush to improve modulation response.
Thermistor check: If fluctuations persist, a technician should test inlet and outlet thermistors and replace if out of spec.

Hot water temperature fluctuates between hot and cold during a shower; no error code displayed.

Possible Causes