Mixergy with a Heat Pump FAQ 

Why does my Mixergy tank behave differently when connected to a heat pump?

Heat pumps heat water slowly and at lower temperatures (typically 45–55°C).

Because of this, the heat pump always performs a full-tank heat, not a partial top-up.

This is different from electric or boiler inputs, where Mixergy can heat only part of the tank.

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Does Mixergy top-heat the tank when using a heat pump?

No. With a heat pump, the system does not heat only the top section.

A heat pump always charges the entire store because it:

• Works slowly
• Works best at stable temperatures
• Needs to run long, continuous cycles for efficiency

Mixergy respects this behaviour rather than interrupting it.

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So what does Mixergy actually improve when the heat pump is running?

Mixergy improves destratification control.

Because the heat pump feeds heat into a fixed point at the bottom of the cylinder through an external plate heat exchanger, Mixergy ensures:

• Hot and cold layers stay separated properly
• The heat pump isn’t forced to reheat already-hot water
• Heat is drawn cleanly from the right place to minimise mixing

This helps the heat pump stay efficient and avoid unnecessary cycling.

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Why is destratification important for my heat pump?

Good destratification means:

• The heat pump sees a clear temperature difference to work against
• It runs smoother and more efficiently
• It doesn’t waste energy by constantly reheating warm water

Poor destratification makes heat pumps work harder and reduces performance.

Mixergy’s sensors and control strategy ensure the layers remain stable.

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How does Boost work when I have a heat pump?

Boost simply requests heat from your heat pump.

• It does NOT use the immersion heater automatically
• It does NOT top-heat the tank
• The heat pump will begin a heating cycle if conditions allow

This means Boost may feel slower than with direct electric heating — that’s normal for heat pump systems.

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Can I Boost using electricity instead of the heat pump?

Yes. If you want faster recovery, you can enable Direct Electric as your secondary heat source:

1. Go to your heat source settings

2. Select “Direct Electric” as the secondary heat source

3. Boost again

The immersion heater will now be used during Boost.

This is useful when:

• You need hot water urgently
• Your heat pump is unavailable
• Demand is higher than usual (e.g., guests, multiple showers)

It will automatically switch back to the heat pump after the boost is finished, as long as "Heat Pump" is set as your primary heat source. 

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Do I need to change anything day-to-day?

No. Once the system is set up, Mixergy and your heat pump work together automatically.

You only need to use Boost if you want faster recovery for unexpected water events. 

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