Should Our Water Circulation Pump Be Configured to Run All The Time?

Air Source Heat Pumps (ASHPs)

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GrahamF

(@grahamf)

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Joined: 6 months ago

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Topic starter 14/10/2025 10:55 am

Our system is open loop with just one zone and FRVs on most radiators. The TRVs in the bedrooms and one sunny lounge are all wide open. We are running weather compensation, which seems to be tuned well.

The water circulation pump in our Grant Aerona 290 15.5kW heat pump is configured to run all the time, regardless of whether the compressor is running. At this moment, the compressor is off and the water is pumping at 1.2m3/hr (20l/min). When the compressor is on, the water flow rate increases.

The Grant support engineer explained that the heat pump has to keep the water flowing around the system, even when the compressor is turned off, so that it knows if the water is at the correct flow temperature. When the water temperature drops too low, it will restart the compressor. I can configure the water pump to turn off when the room temperature reaches the target set on the room thermostat, but then I won't be getting the full benefits of weather compensation and the compressor will cycle more.

My concerns are that this is wasting a bit of electricity and it is imposing unnecessary wear and tear on the water pump. On a hot day, the compressor might need to run only 2 hours per day to heat the hot water, but the water circulation pump will still run 24 hours per day.

I would be interested to know how other people's systems handle this and what you would do if you had our system.

Technical Details

The Pump Blockade parameter is set to No, which makes the pump run all the time. When the room reaches the temperature target set on the room thermostat, the pump is supposed to reduce the flow temperature to maintain that room temperature.

We could change Pump Blockade to Yes. In that case, the water pump and therefore the compressor would turn off when the room reaches the emperature target set on the room thermostat.

Here is the relevant section from Grant Aerona Smart Heat Pump System Controller Installation & Operating Instructions

GRANTUK.COM "https://www.grantuk.com/media/6037/grant-aerona-smart-controller-installer-and-operating-instructions-uk-doc-0203-rev-20-october-2024.pdf"

7.8.1 THERMOSTATIC PUMP BLOCKADE

Thermostatic pump blockade is a hydraulic control feature within the heating circuit setting that enables the Grant Aerona Smart controller to either switch a circuit pump/valve OFF (Thermostatic Pump blockade ON) or keep the circuit active (Thermostatic Pump blockade OFF) based on the status of an installed thermostat monitoring the circuit.

If a thermostat has been installed on any heating circuit, you have the following choices in how to control that circuit:

With pump blockade 'ON' - Each heating circuit thermostat will control the circulating pump or motorised valve (whichever is installed) for that circuit based on the air temperature the sensor/thermostat is monitoring.
With pump blockade 'OFF' - The heating circuit will continue to have circulating pump or motorised valve enabled (whichever is installed) but the smart controller will drive down the flow temperature to the minimum value to maintain the target air temperature within the circuit i.e the circuit remains active. This option would be best suited for open loop room optimisation.

Grant Aerona 290 15.5kW, Grant Smart Controller, 2 x 200l cylinders, hot water plate heat exchanger, Single zone open loop system with TRVs for bedrooms & one sunny living room, Weather compensation with set back by room thermostat based load compensation

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dgclimatecontrol

(@dgclimatecontrol)

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Joined: 2 months ago

Posts: 39

14/10/2025 11:21 am

This is often a problem when units are installed under a grant scheme. Some have two or three pumps running all the time! They should always be controlled by the heat pump controller and never wired separately or controlled by a central heating stat.

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