When replacing an externally controlled circulation pump, a matching thread and a similar model name are not enough. Using the Wilo Varios PICO-STG 25/1-7, manufacturer product number 4215542, this guide explains which mechanical and electrical specifications need to match. These checks help you prepare the replacement selection with your contractor.
Identify the exact version
The Wilo Varios PICO-STG 25/1-7, product 4215542 has an installation length of 180 mm. The threaded connection on the pump housing is specified as G 1½. It requires an electrical supply of 1 × 230 V. Do not assume these details also apply to other versions in the same series.
Before selecting a replacement, photograph the existing pump’s rating plate and any accessible connection markings. Add the exact model designation of the heat generator or pump assembly. The old series name alone is often insufficient for a reliable compatibility check. You need to know which version, including its pump curve and control arrangement, was fitted in the particular appliance.
What do iPWM GT and iPWM ST mean?
The listed model supports external control via iPWM GT for heating and geothermal applications, or iPWM ST for solar applications. The product data assigns the two signal types to different uses. This does not establish blanket replacement compatibility with every appliance that has a PWM connection.
Check the signal type required by the system controller, the terminal assignment and the specified replacement configuration against the manufacturer’s documentation. The 230-volt supply and control connection are two separate selection criteria. A mechanical connection that fits does not establish electrical or control compatibility.
Which settings are available?
There are three predefined curves each for constant and variable differential pressure. Three constant-speed settings are also available. A Sync function allows reprogramming when replacing a pump. The settings to use depend on the application and the confirmed replacement match.
This choice of settings allows different control arrangements to be considered. It does not replace a comparison of the required hydraulic performance. Have the appropriate pump curve and settings determined before commissioning.
Four checks before replacement
- Identification: Record the complete designations of the old appliance and pump, including the product number.
- Installation: Compare installation length, connection threads, mounting orientation and available space.
- Control: Check the mains supply, required PWM profile, terminal assignment and any necessary configuration.
- Operation: Check the required flow, head and permitted conditions against the technical documentation.
HKS Energy recommends this model when all four checks confirm a suitable match. Then have the setpoints, selected control mode and operation within the system documented. The Varios PICO-STG 4215542 product page provides the model-specific information and technical documents needed for this comparison.