Combine solar and a heat pump

In a compatible installation, solar panels and an external heat pump can both help heat the water in your Mixergy tank. Spare solar means electricity your panels generate that the rest of your home is not using. A heat pump transfers warmth into the tank through the connected heating system.

Heating may pause, change source or progress more slowly than you expect. This does not always mean something is wrong.

How do the heat sources work together?

The exact setup depends on how the system was designed and installed. In a typical compatible system:

• Spare solar electricity can heat water during the day.
• The heat pump provides hot-water heating through a longer, gradual cycle.

The immersion heater can also provide backup if your installer has configured it that way. It can help complete the cleansing cycle, which heats the tank fully to help control bacteria in stored water.

The immersion heater is the electric heating element inside the tank. It should only be used as the system has been configured.

Check the main settings

For a combined external heat-pump and solar system, Mixergy normally recommends Heat Pump as the default source. Keep the setting your installer confirmed for your system.

To view the source, open the Mixergy app, select your tank and choose Heat Source in the main menu. Automatic Mixergy Flex settings also specify the source used for automatic schedules.

For supported Mixergy solar controls, open the top-right menu, choose Tank Settings and look for PV Diverter Settings or PV Diverter Schedule. Use spare PV to heat tank allows spare solar heating when enabled. A third-party diverter uses its own controls instead.

Do not copy the settings used in another home. Ask the installer, landlord or housing provider to confirm the correct heat source, solar settings and backup arrangement.

How does Mixergy decide what to use?

The tank considers when hot water is needed, the available spare solar electricity and what the heat pump can provide. Your schedule, energy tariff, cleansing cycle and frost protection can also affect the timing.

The tank may wait for solar instead of using grid electricity straight away. If there is not enough solar and the heat pump can provide the heat, the heat pump can finish the cycle. An approved immersion heater may run when needed for backup or safety heating.

A change of heat source does not automatically mean the solar system or heat pump has failed.

What can I check if there is not enough hot water?

Start by checking whether the problem is a lack of hot water or simply unexpected heating times.

1. Open the Mixergy app and select your tank. Read the hot-water level and heating status. Without the app, use the red level lights on the gauge, the slim black panel on the tank.
2. Read the heat pump’s own display. If it shows a fault, record the message and contact the installer. Avoid changing technical settings to clear it.
3. During a bright period, read your solar system’s display to see whether it is generating. Open Graphs in Mixergy and choose PV Power if available. With a third-party diverter, read its own display as well.
4. Use the Tank Settings route above to read the solar setting, if your setup provides it. See Solar settings explained before making a change.
5. Open the top-right menu and select Mixergy Flex. Standard or Economy means automatic heating is active; Off means you need a manual schedule. See Set schedules and smart control for the setup instructions.
6. Record when the problem happened and what each display showed.

Contact the installer or housing provider if the heat pump repeatedly stops, solar is never used in suitable conditions or the household regularly runs out of hot water.

What can affect performance?

The system may not work as expected if:

• The heat source is set incorrectly.
• Use spare PV to heat tank is switched off.
• The solar diverter cannot detect spare electricity.
• The water leaving the heat pump has reached the temperature limit set for it. This is called its flow-temperature limit.
• Space heating has priority.
• Installer settings limit the hot-water cycle.
• The tank is already at its solar charge limit.

A CT clamp is the sensor around a cable that measures electricity flow. Leave it in place and do not open electrical equipment. Your installer should carry out technical checks or change advanced heat-pump controls.

Can I use the system without the app?

Yes. The installed controls can continue to work, and you can check or boost hot water using the gauge. The app provides more information and access to settings.

Common questions

Why is the tank waiting on a sunny day?

Sunshine does not guarantee spare electricity; your household can be using what the panels generate. The tank can also wait for expected solar. If you need extra hot water, request a Boost using the gauge’s up arrow. Allow time for heating; a Boost is not instant hot water.

Why is heating continuing after sunset?

The heat pump or an approved backup source may be completing the amount of hot water requested.

Why did the immersion heater turn on?

It may be providing approved backup or helping to complete the cleansing cycle. Ask the installer if it runs often and you do not know why.

Which heat source should I select?

For a combined external heat-pump and solar setup, Heat Pump is normally the recommended default. Electric and Indirect is a different arrangement, typically involving a boiler. Follow your installer’s confirmed setting rather than copying another home.

Why does the solar graph show nothing while the tank heats?

The heat pump may be heating the tank, or a third-party solar diverter may not report its power to Mixergy. Check the heat pump and diverter displays.