Heat pump secondary pump control coordinates the indoor circulation pump with an air-to-water heat pump when a plate heat exchanger separates the outdoor and indoor water circuits. The practical solution is to connect the indoor pump through the designated control interface, match the electrical connection to the pump, and commission both circuits together.
EXINDA, an air-to-water heat pump manufacturer serving European installers and distributors, provides a second circulation-pump interface on applicable configurations. This guide explains how to use that feature to address a common integration question: how should an independently pumped indoor circuit respond when the heat pump needs to deliver heating or cooling?
Why can a running heat pump leave the indoor circuit poorly supplied?
A plate heat exchanger transfers heat between two separate fluids; it does not transfer water from one circuit to the other. The heat pump's internal circulation pump moves fluid through the outdoor circuit. A separate pump moves water through the indoor circuit.
If the indoor pump is not running when needed, or its flow is inadequate, heat transfer to or from the building can be restricted even while the heat pump-side pump is operating. Pump coordination is therefore part of system commissioning, alongside flow, air removal and valve operation.
Step 1: Identify the two circuits and their required flow
Mark the heat pump, separating plate heat exchanger, indoor emitters, pumps and zone valves on the hydraulic schematic. Identify which pump serves each circuit and where each circuit's flow can be measured.
Use the design flow and pressure-drop requirements to select the indoor pump. Include the plate heat exchanger, pipework, valves and emitters in that assessment. Where the outdoor circuit contains glycol, use the fluid concentration and temperature in its hydraulic calculation. The two circuits do not automatically require identical flow rates or pump settings.
Step 2: Use the designated EXINDA second-pump interface
For the applicable EXINDA configuration, the designated second circulation-pump interface provides the connection point for integrating the indoor pump. Obtain the wiring reference for the installed model and control-board version before preparing the connection.
Match the terminal designation to its documented function. A domestic-hot-water circulation output serves a different purpose and should not be substituted for the indoor heating or cooling pump output.
Step 3: Match the control output to the pump
A qualified installer should isolate the electrical supplies and follow the model-specific wiring diagram. Check these items before connection:
| Check | Installation action |
|---|---|
| Output type | Identify whether the interface supplies switched power, a dry contact or another control signal. |
| Pump requirements | Check the supply voltage, running current, starting characteristics and any external enable input. |
| Output rating | Compare the pump load with the documented switching capacity. Use the specified relay or contactor arrangement where required. |
| Protection and isolation | Provide the electrical protection, earthing and isolation required by the equipment instructions and installation design. |
Use a signal input only with the signal it is designed to accept. A pump-control command and a pump power supply are separate functions unless the wiring documentation explicitly combines them.
Step 4: Set the heat pump secondary pump control sequence
Define what the indoor pump should do when heating or cooling is requested, while demand continues and after demand ends. Coordinate the heat pump's documented sequence with thermostats, zone valves and any existing indoor pump controller.
Include domestic-hot-water priority, defrost, frost protection and post-run functions where they apply to the selected system. Follow the documented sequence for each mode rather than imposing identical start and stop times on both pumps. Ensure that the necessary water path remains available when circulation is requested.
Step 5: Commission the command and the water flow
Fill and vent the circuits, check strainers and valve positions, and establish the intended pump settings. Then test the control response and actual circulation:
- Create a heating or cooling demand. Check that the designated output activates and that the indoor pump responds.
- Verify flow on both sides. A running motor alone does not prove that water is circulating at the required rate.
- Record temperatures. Measure entering and leaving temperatures on both sides of the separating heat exchanger once operation stabilises.
- Change zone demand. Check the response as the relevant zones open and close.
- Remove demand. Verify the documented stop or post-run sequence and any remaining active request.
Record the wiring-diagram revision, pump settings, measured flows and operating temperatures in the commissioning record. This gives the installation partner and EXINDA a useful baseline for future technical review.
What should installers check if the indoor pump does not respond?
| Observation | Next check |
|---|---|
| No pump command | Check the active demand, operating mode, output assignment and configured sequence. |
| Command present, pump stopped | Check the pump supply, enable connection, relay or contactor, protection devices and pump status. |
| Pump running, little circulation | Check trapped air, closed valves, blocked strainers, flow direction and the pump duty point. |
| Flow present, weak heat transfer | Review both circuit flows, the four heat-exchanger temperatures, exchanger selection and fouling. |
| Pump continues after demand ends | Compare the behaviour with post-run, protection and other active control requests. |
Frequently asked questions
Can an indoor circulation pump connect to an EXINDA heat pump?
Yes. Applicable EXINDA configurations provide a designated second circulation-pump interface. Use the model-specific wiring information to establish the output type, electrical connection and operating sequence.
Does adding a second pump automatically solve poor heat transfer?
The pump must deliver the required flow and operate at the right time. Check pump selection, valves, air removal and both sides of the heat exchanger together.
Should the indoor pump always copy the internal pump?
Use the documented operating sequence. Heating, cooling, domestic-hot-water priority and protective operation can require different circulation arrangements.
Plan the pump connection with EXINDA
For a European air-to-water heat pump project, send the selected unit identification, hydraulic schematic, indoor pump specification and intended control sequence to your EXINDA supply partner or info@exindagroup.com.
EXINDA supports the product-side interface review and provides the applicable connection information. The local installer completes the site wiring, hydraulic checks and commissioning. This turns the second-pump connection into a defined, testable part of the installation.
Explore EXINDA R290 heat pump support for installers for related project and product support.
