Purge Pumps


Kensa recommend the Clarke SPE1200SS (part no. 051012200) to purge ground arrays in order to remove air in the pipes to avoid the heat pump system freezing

The pump comes ready to take a 1” BSP fitting.

As a kit, Kensa Heat Pumps provides 2 x 1” BSP Male Iron to 28mm Speedfit connectors. This will enable the pump to be connected to the slinky manifold using 28mm Speedfit or similar pipes and elbows.


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It is advised that installers purchase a Clarke purge pump to enable commissioning of future systems. The Clarke SPE1200SS can achieve as much as 5 bar pressure against a closed valve, so ensure the connections to the pump and manifold are robust.

It is important for correct operation of the heat pump that all the air is removed from the ground arrays before the heat pump is turned on. Failure to do this correctly can cause the heat pump evaporator heat exchanger to freeze and the heat pump to stop working. If this happens then the only option is to allow the heat pump to defrost by leaving it for at least 24 hours and then re-purge the ground arrays.

Slinky ground arrays consist of a large number of 1m diameter loops of 32mm OD pipe and air can collect at the top of these loops. Even vertical (i.e. drilled) arrays can have trapped air and should be purged.

To remove the air from ground arrays, a suitable pump will be required. For slinkies, the longest slinky trench is 50m, which will contain a total of approximately 300m of pipe. To achieve the minimum velocity required to remove the air, a minimum pump power in excess of 1kW is required. In addition, the pump needs to have a flow of at least 60 litres per minute against a pressure of at least 1 bar. To achieve this, a multi-stage pump is required.

A normal rising cold water main in a building has insufficient flow to force out this air. Mains water is also “aerated”, so should not be used.

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