STIEBEL ELTRON WPL 25 AC

Compatibility

Compatible with EpiSensor Edge over Modbus TCP through an ISG

The May 2026 ISG compatibility table includes WPL 15/20/25 A(C)(S) with WPMsystem and WPM 3. The current Modbus software document explicitly covers ISG Connect, web and plus and supplies controller-specific read tables. ISG Connect includes Modbus software at the factory.

Match the installed WPM and ISG to the compatibility row, including manufacturing-date/software conditions. Use the published map as a best-effort starting point, compare the first read with the WPM display and handle unavailable objects. This procedure covers monitoring; preserve the existing SG Ready and output-control design.

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Models

Specifications

STIEBEL ELTRON identifies the WPL 25 AC as an outdoor air-to-water heat pump, order 236645, for heating and cooling. The current product page gives 7.84 kW at A7/W35, 12.86 kW at A-7/W35 and SCOP 4.76 at 35°C; these are different test conditions, not a continuous output range. A WPM wall-mounted heat-pump manager is required equipment.¹

Exact outdoor unit

WPL 25 AC, order 236645; outdoor air-to-water heat pump¹

Heating output

7.84 kW at A7/W35; 12.86 kW at A-7/W35 (EN 14511)¹

Seasonal rating

SCOP 4.76 at 35°C (EN 14825); not a site COP measurement¹

Required controller

Wall-mounted WPM, order 234727 on the German product listing¹

BMS interface

Compatible ISG accessory can present Modbus TCP; the outdoor-unit X43 is internal^2, 3, 4

SG Ready

WPL 25 AC is labelled SG Ready; WPMsystem inputs X1.13-1 and X1.13-3 are described in the ISG Connect manual^1, 3

Controller boundary

Confirm WPMsystem or WPM 3, ISG type, manufacturing date and minimum software before integration^2, 3

Interface

Documented measurements and integration boundaries for WPL 25 AC.

• The ISG is the local Modbus TCP endpoint. Its CAN connection communicates with the WPM; the outdoor unit X43 label belongs to the internal heat-pump circuit.
• The current map lists outside temperature at one-based input address 507 for WPMsystem and WPM 3. Use FC04, one 16-bit word, signed type 2 with a 0.1 multiplier to obtain °C. Try zero-based client address 506 and compare the value with the controller.
• Input addresses 515 and 516 give actual flow and return temperatures, and 522 gives actual DHW temperature, where the sensor/object is available. These are signed type-2 values scaled by 0.1 °C. The separate heat-pump-1 rows include return temperature 542 and flow temperature 543; choose the point that matches the system display.
• The substitute value 32768 (0x8000) means an object is unavailable. Check it before signed conversion, omit that sample and retain its unavailable status rather than displaying -3276.8 °C.
• The software document says ISG addresses are one-based and a client offset of one may be needed. Keep the published address, client convention, type and multiplier with each point; type 7 uses a 0.01 multiplier, unlike type 2.
• WPL 25 AC is labelled SG Ready. WPMsystem input contacts and ISG Modbus control registers support separately commissioned functions. Establish monitoring first and preserve existing heating, DHW and frost-protection settings.
• For site COP, meter delivered heat and the complete electrical input over matching periods. Controller operating values help explain performance; independent meters define the measured boundary.

Setup

1. Identify the installed system

   Record WPL 25 AC order 236645, WPM type, manufacturing date and ISG model. Match the manufacturer compatibility row; the July 2015 WPM 3 row names WPM 390.03 and FES 417.02 minimum versions.

2. Connect the ISG

   For ISG Connect, use the supplied CAN cable on the commissioned WPM bus, LAN cable to the site network and USB-C power adapter. Allow the documented 5-10 minute WPM initialisation and check the left LED is steady green.

3. Find its local address

   Use SERVICEWELT or the router DHCP list to identify the ISG IP. The documented direct-connection address is 192.168.0.126. Keep the Modbus service inside the protected site network.

4. Read outside temperature

   Start with FC04, one register, trying zero-based address 506 for the map’s one-based address 507. Reject 0x8000 as unavailable; otherwise decode signed 16-bit and multiply by 0.1 °C. Compare with the WPM outside-temperature display.

5. Add available points

   Use the table for WPMsystem or WPM 3. Try actual flow 515, return 516 and DHW 522 using the same type-2 scaling, then compare each with its matching display value. Save only useful points that the installed system reports.

6. Meter performance and preserve controls

   Meter delivered heat and full electrical input separately for COP. Record valid-read timestamps and unavailable samples. Leave SG Ready, output reduction and mode/setpoint writes in the commissioned heat-pump design.

Common questions

Does WPL 25 AC have a direct Modbus TCP server?

Use a compatible ISG connected to the WPM. ISG Connect has a local Modbus TCP service and the current software document supplies separate WPMsystem and WPM 3 tables. Start with the published outside-temperature address 507, using FC04 and signed 0.1 °C scaling.^2, 3, 5

Does the SG Ready label mean Edge may dispatch the heat pump?

SG Ready provides control functions through the installed WPM/ISG and commissioned input wiring. Plan permitted modes, override and fallback separately from monitoring, then measure the electrical response.^1, 3

Can WPM 3 and WPMsystem use the same setup?

Both appear in the manufacturer’s WPL 15/20/25 A(C)(S) compatibility table. The WPM 3 row for units from July 2015 names specific WPM 390.03 and FES 417.02 versions; confirm the installed row instead of assuming the controllers are interchangeable.²

Can the product SCOP be used as measured site COP?

No. SCOP 4.76 is a standardised 35°C rating. A site COP needs independently metered delivered heat and complete electrical consumption over matching intervals.¹