H08
Panasonic
Heat Exchanger Overheat / Safety Thermostat Trip
Panasonic water heater shows H08 and shuts down; may be associated with very hot outlet water.
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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
Tripped overheat thermostat on heat exchanger, Blocked water flow through heat exchanger, Scale buildup inside heat exchanger, Faulty circulation within heater
How to Fix / Troubleshooting
Burn hazard: Water and internal parts may be extremely hot. Turn OFF power and allow the unit to cool completely before working on it.
- 1. Check water flow:
- Ensure hot water taps are fully open and not restricted.
- Clean aerators and shower heads to improve flow.
- 2. Inspect inlet filter: Clean the cold water inlet filter screen to restore proper flow through the heat exchanger.
- 3. Reset overheat thermostat (if manual reset type and allowed by Panasonic manual):
- Remove the front cover.
- Locate the overheat thermostat on the heat exchanger (small disc‑type device).
- Press the reset button if present and specified in the service manual.
- 4. Descale heat exchanger (qualified persons):
- Isolate the heater with service valves.
- Connect a descaling pump and circulate approved descaling solution through the heat exchanger according to Panasonic instructions.
- 5. If H08 recurs: The overheat thermostat or heat exchanger may be damaged and should be inspected and replaced by an authorized technician.
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Repair Difficulty
Hard
4/5
Required Part
Overheat Thermostat on Heat Exchanger
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