Balancing a domestic heat pump system is essential, often more so than with boilers, because heat pumps operate at lower flow temperatures and rely on high, consistent flow rates for efficiency. Balancing should be completed during commissioning. If not done correctly, the heat pump may short-cycle and lose efficiency.
Key considerations for balancing a heat pump heating system
Preparation
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Ensure the system is filled, vented, and correctly pressurised.
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Set the heat pump to heating mode (not DHW).
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Run the system at a steady load; allow more time than you would for a boiler.
Radiators
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Fully open all lockshield valves and set TRVs to maximum.
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Aim for a temperature drop of around 5°C across each radiator.
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Begin by throttling radiators closest to the heat pump, then work outward until all radiators meet the target temperature drop.
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Expect nearby radiators to be more restricted and distant ones more open.
TRVs:
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Ensure they are suitable for low-temperature systems.
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Set the weather compensation curve so TRVs remain mostly open, only trimming excess heat.
Bypass:
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Use an automatic bypass valve or leave one radiator/towel rail without a TRV.
Handover note: Clarify to the homeowner that the heat pump’s controls manage the system, and TRVs simply fine-tune comfort.
Underfloor Heating (UFH)
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UFH operates at a lower flow temperature than radiators.
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If UFH and radiators share a pump, use a mixing valve on the UFH manifold.
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If they have separate pumps, set each to deliver the design flow.
Balancing UFH loops:
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Set all UFH thermostats to maximum.
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Use the manifold flow meters and return lockshields to adjust each loop to its design flow and temperature drop.
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Confirm the total manifold flow matches the system design.