Hoval PV-Heater

Use cases

• Monitor water temperature and actual heater load on a live cloud dashboard for each customer site.
• Set the power step remotely to match real-time PV surplus and avoid grid feed-in.
• Create an alert when emergency mode activates, indicating a potential overtemperature or communication fault.
• Log total energy consumed by the PV-Heater over time to generate monthly self-consumption reports.
• Adjust the temperature limit remotely to match seasonal heating demand without an on-site visit.
• Track actual load versus load setpoint to verify the heater responds correctly to control commands.

Installation

1. 1Wire the Modbus gateway to the Hoval PV-Heater using Modbus RTU (RS-485 two-wire) or connect via Modbus TCP over Ethernet to the same network segment.
2. 2Open the PV-Heater web interface and activate Modbus TCP or Modbus RTU, depending on your wiring choice.
3. 3Set the rotary temperature controller on the PV-Heater housing to maximum (85°C) so that Modbus-based temperature limits take effect.
4. 4Configure the Modbus slave address on the PV-Heater to match the address set in the ModbusCloud gateway.
5. 5Import the Hoval PV-Heater template in the ModbusCloud platform and assign it to the connected gateway.
6. 6Set the repetition interval to 7 seconds in the gateway configuration to ensure continuous communication with the heater.

Things to watch for

01

The PV-Heater keeps rebooting when connected via Modbus TCP. What is wrong?

There is a known issue when using Modbus TCP with AVM or Fritz Box routers. The heater times out and reboots repeatedly. Use Modbus RTU or 0-10V control as a workaround until a network-command-based template is released.

02

Why do all actual values drop to zero after a short time?

If the PV-Heater does not receive new Modbus values within 60 seconds, it resets actual values to zero as a safety fallback. Ensure the repetition interval is set to 7 seconds and that the gateway maintains a stable connection.

03

How is the temperature register encoded?

The temperature register at address 325 uses float32 encoding. The template handles this automatically, so no manual byte-order conversion is needed.

04

Do I need to adjust the physical thermostat on the heater?

Yes. Set the rotary temperature controller on the housing to maximum (85°C). This allows the Modbus temperature limit to govern operation. If the dial is set lower, the physical thermostat may cut off the heater before the Modbus setpoint is reached.

Registers (8)

4 read / 4 write

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