How to Fix / Troubleshooting

Safety: Turn OFF power and water before opening the heater. Beware of hot water when testing.

Stabilization steps:

Check that the shower valve is not a thermostatic or pressure-balanced type that conflicts with the tankless heater. If it is, adjust or replace with a model compatible with tankless heaters.
Ensure that no other large water demands (toilets, washing machines) are cycling on and off during use, causing pressure swings.
Remove the heater cover and clean the inlet filter screen and flow sensor to ensure smooth, accurate flow detection.
Descale the heat exchanger and elements if there is evidence of mineral buildup.
Try slightly reducing the temperature setpoint to reduce the heater's modulation range and improve stability.

If fluctuations persist, the flow sensor or control board modulation algorithm may be faulty and require part replacement.

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

Possible Causes