Rheem
Inconsistent Outlet Temperature / Flow Modulation Issue
Rheem tankless water heater delivers hot water but temperature fluctuates up and down during a shower
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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
Minimum flow not maintained, Mixing with cold at fixture, Scale in flow sensor or heat exchanger, Inlet temperature swings
How to Fix / Troubleshooting
Safety first: Water temperature swings can cause discomfort or scalding. Test carefully.
- Adjust usage: Open the hot tap more and reduce mixing with cold at the shower valve. Many tankless units need a minimum flow to stabilize.
- Clean inlet filter and flow sensor: Remove and clean the inlet filter screen. Inspect and clean the flow sensor impeller if accessible.
- Descale: Perform a descaling flush to restore proper heat transfer and modulation.
- Check shower valve: Thermostatic or pressure-balancing valves can malfunction; service or replace if they cause mixing issues.
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Repair Difficulty
Medium
3/5
Required Part
Flow Sensor Assembly
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