Askoma ASKOHEAT+
The Askoma ASKOHEAT+ is a Power-to-Heat immersion heater designed for direct installation in hot-water storage tanks and buffer tanks, converting surplus PV or grid energy into stored heat. This ModbusCloud template reads the device over Modbus TCP and exposes actual heater load, tank temperature from the integrated PT1000 sensor, the configured safety temperature limit, and the energy-manager power setpoint via a readable and writable register at address 319. Use it to integrate the ASKOHEAT+ into automated solar self-consumption workflows from your ModbusCloud portal.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 5, read and write
- Brand
- Askoma
- Last updated
Registers (5)
4 read, 1 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| setmaxpower | W | Write | |||
| getmaxpower | W | Read | |||
| power | W | Read | |||
| temp | °C | Read | |||
| limittemp | °C | Read |
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Use cases
- Monitor actual heater power in real time to verify the ASKOHEAT+ is consuming PV surplus as instructed.
- Track tank temperature over time to detect heat loss patterns or insulation degradation in the storage vessel.
- Alert on tank temperature exceeding the configured safety limit to catch thermostat or sensor faults early.
- Compare the written power setpoint against actual heater load to verify the energy manager commands are accepted.
- Report daily heating cycles and power curves to building owners as evidence of PV self-consumption performance.
Installation
Connect the ASKOHEAT+ to your local LAN using a CAT5 or better Ethernet cable and confirm it receives an IP address via DHCP, or assign a static address through your router to prevent it from changing.
Open a browser and navigate to http://askoheat.local or the device IP address to reach the web interface, then verify Modbus TCP is active on port 502 under the communication or Modbus section.
In the ModbusCloud portal, add a new ModbusCloud Gateway on the same network, import the Askoma ASKOHEAT+ template, and enter the device IP address. The unit ID is not relevant and can remain at the default.
Spot-check the connection by reading the power register (address 317) in the portal live view: a value of zero indicates the heater is idle, any non-zero watt reading confirms polling is working correctly.
Things to watch for
Register reads return zero even though the heater is running. Why?
Register 317 (power) reports zero if the safety temperature limiter or thermostat has cut out, even when relay contacts are closed. Check the tank temperature against the configured limit in register 640. If the limit is reached, the heater disables and load drops to zero until the tank cools.
The gateway connects on port 502 but values appear stale or never update.
The ASKOHEAT+ updates its Modbus data every second and considers a connection interrupted after 5,000 milliseconds of silence. Set your polling interval to no faster than one second and ensure no firewall or managed switch is blocking TCP port 502 between the ModbusCloud Gateway and the heater.
Writing the power setpoint has no effect on the heater output.
Register 319 (setmaxpower) is an energy-manager setpoint. If the ASKOHEAT+ has not had a Modbus command within the last 60 seconds, it clears this setpoint automatically for safety. Ensure the ModbusCloud Gateway writes the value at least once per minute, and confirm the device is in energy-manager mode via the web interface.
Is it safe to write large watt values to the power setpoint register?
Use caution when writing to register 319. The ASKOHEAT+ will attempt to match the requested load, but setting a value beyond the heater's rated capacity or above the configured temperature limit can trigger the safety limiter, potentially disrupting legionella protection schedules. Always verify the written value does not exceed the device's rated power.
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