Rheem
Unstable DHW Temperature Control
Boiler produces fluctuating domestic hot water temperature (hot-cold-hot cycling)
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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
Faulty DHW flow sensor, Scaled plate heat exchanger causing rapid temperature swings, Incorrect minimum modulation settings, Mixing valve malfunction
How to Fix / Troubleshooting
Safety first: Be cautious of sudden hot water temperature changes that can cause scalding.
- Step 1 – Check DHW flow: Ensure a steady flow at the tap. Very low or very high flow can cause instability. Adjust flow to a moderate level.
- Step 2 – Inspect DHW flow sensor: Clean or replace the DHW flow sensor if it is sticking or giving erratic readings.
- Step 3 – Descale plate exchanger: Scale can cause localized overheating and rapid cycling. Have a technician descale the DHW plate heat exchanger.
- Step 4 – Mixing valve: If an external thermostatic mixing valve is installed, verify its operation and replace if it is sticking or misadjusted.
Warning: Persistent temperature swings should be addressed promptly to avoid scalding, especially for children or elderly occupants.
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Repair Difficulty
Medium
3/5
Required Part
DHW Flow Sensor
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