The E.G.O. Smart Heater is a screw-in immersion heater (Einschraubheizkörper) designed to convert surplus photovoltaic energy into hot water. Manufactured by E.G.O. Elektro-Gerätebau GmbH, it is available in two variants: RS485 Modbus RTU (29.65335.000) and Ethernet Modbus TCP (29.65335.100). The TapHome template connects via Modbus TCP to the Ethernet variant.
The heater provides three independent relay stages — 500W, 1000W, and 2000W — for a maximum output of 3500W in 500W increments. The template supports both manual power control and automatic mode, where the heater adjusts its power output based on total house consumption.
Hardware connection
The Ethernet variant (29.65335.100) connects directly to the local network via an Ethernet cable. No additional gateway or converter is required for Modbus TCP communication.
- Protocol: Modbus TCP
- Port: 502
- Slave ID: 247 (fixed, not configurable)
- Power supply: 230V / 16A (separate 16A fuse required)
- Installation: Horizontal only — vertical installation is not permitted
The RS485 variant (29.65335.000) requires an RS485-to-TCP converter to work with TapHome via Modbus TCP. The wiring terminals are: A (Data+), B (Data−), C (GND). Connect the cable shield on one side only. Communication parameters for the RS485 variant: 19200 baud, even parity, 1 stop bit.
Configuration
No software configuration is required on the heater itself. The rotary selector on the device controls the maximum water temperature (40°C, 60°C, or 80°C) and operating mode (OFF / Frost Protection / Heating).
When importing the template in TapHome, provide:
- IP Address — the heater’s IP on the local network
- Slave ID — fixed at 247 (do not change the default)
Assign a static IP address or DHCP reservation to the heater in the router settings to prevent the address from changing after a power cycle.
Device capabilities
The template exposes 10 devices for power control, temperature monitoring, and relay status tracking.
Power control
Two writable variables control the heater’s operating mode:
Power Nominal Value — manual power setpoint in watts (0–3500W in 500W steps). Write a specific power level to activate manual mode. Write -1 to switch to automatic mode, which enables evaluation of the Home Total Power register. The activation signal must be refreshed every 60 seconds or the heater deactivates automatically (safety feature).
Home Total Power — total house power consumption in watts (Int32). In automatic mode (after writing -1 to Power Nominal Value), the heater reads this value and automatically selects the optimal relay combination based on available excess power. Negative values indicate grid export and trigger heating activation.
The 60-second timeout is a safety feature. TapHome must write to Power Nominal Value at least once per minute. If communication is interrupted, the heater will deactivate automatically.
Temperature monitoring
- Boiler Water Temperature — current water temperature in °C (read-only). The heater continues heating until the maximum temperature set by the rotary selector is reached.
- Minimum Temperature Threshold — minimum boiler temperature in °C before automatic heating activation (read-only in the template).
Relay monitoring
Each of the three heating relays has individual power and operating time tracking:
| Relay | Power stage | Actual Power | Operating Seconds |
|---|---|---|---|
| Relay 1 | 500W | Current power consumption | Total operating time |
| Relay 2 | 1000W | Current power consumption | Total operating time |
| Relay 3 | 2000W | Current power consumption | Total operating time |
The relay power readings show 0W (off) or the rated wattage when active. Operating seconds are cumulative counters that persist across power cycles.
Additional capabilities
The E.G.O. Smart Heater also exposes Modbus registers for PCB temperature monitoring, maximum temperature configuration, desired water temperature setpoint (software-controlled target temperature), total device operating time, total heating time, cumulative energy consumption, potentiometer position reading, relay status bitmask, relay switching cycle counters, and per-relay minimum ON/OFF time configuration. These can be added to the TapHome template in a future update.
Troubleshooting
No Modbus communication
- Verify the Ethernet cable is connected (for the 29.65335.100 variant)
- Confirm the IP address — check the router’s DHCP lease table
- Ensure TapHome Core and the heater are on the same network/subnet
- Check that no firewall is blocking port 502
- Use Slave ID 247 — this is fixed and cannot be changed
Heater deactivates unexpectedly
The most common cause is the 60-second activation timeout. TapHome must write to the Power Nominal Value register at minimum once per minute. Check the TapHome log for Modbus write errors or communication timeouts.
LED status indicators
The status LED on the device provides diagnostic information:
| LED Pattern | Meaning |
|---|---|
| Steady green | Communication OK, heating OFF |
| Green blinks (1–7×) | Active heating — number of blinks indicates power level (1 = 500W … 7 = 3500W) |
| Continuous green blink | Maximum temperature reached |
| Steady orange | Frost protection active, temperature OK |
| Steady red | Communication to control unit disrupted |
| Blinking red | Serious error — power cycle the device |
