What it means
Samsung's control kit manual lists 'DHW tank temperature sensor error'. The Installer Reference Guide lists 'Water TANK Sensor SHORT / OPEN'.
What to check, in order
- Reset once
Switch the heat pump off at its isolator, wait about a minute and switch back on. If the code returns, it needs an engineer.
- Write the code down
Note the code and whether hot water still heats, so your installer knows what to bring.
When to call your installer
Call your installer. They will check the tank sensor and its connection, and replace the sensor if it has failed.
A repair visit will usually check the sensor's reading and its wiring.
- Note the model and serial number. They're on a label on the rating plate on the outdoor unit, and on the indoor unit or cylinder.
- Write down the exact code, and what the appliance was doing when it appeared.
- Check whether it's still under warranty. If it is, the repair may cost you nothing.
Quick answers
What does the Samsung E904 error code mean?
The temperature sensor in the hot water (DHW) tank is reading as a short or open circuit, so the heat pump cannot tell how hot the tank is. Samsung's control kit manual lists 'DHW tank temperature sensor error'. The Installer Reference Guide lists 'Water TANK Sensor SHORT / OPEN'.
Can I fix Samsung E904 myself?
Engineer only (engineer visit). Start with: reset once; write the code down. Call your installer. They will check the tank sensor and its connection, and replace the sensor if it has failed.
Is Samsung E904 worth repairing?
Worth fixing. A tank sensor or its connection is a small repair and worth doing.
Checked against
- Samsung MIM-E03CN EHS control kit installation manual (PDF), error codes part 2 (ManualsLib copy)
- Samsung EHS Mono (R32) Installer Reference Guide (PDF), troubleshooting of error codes (ManualsLib copy)
Last reviewed October 2026. Manufacturers update their pages, and your manual is the final word. Spotted a mistake? Email contact@appliance-error-codes.com.