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Understanding heat sources

Learn how to select the correct heat source in the Mixergy app so your tank heats efficiently. 

The heat source setting tells the tank where it should expect heat to come (a gas boiler, a heat pump, etc).

If the wrong heat source is selected, the tank will default to using the immersion heater. This will still heat your water, but it may not be the most appropriate or efficient setup for your home. 

What is the Best Option for You?

The guide below outlines the heat sources that can be selected, and the situations in which they can be used. 

Electric Boilers and Solar PV 

Select one of the following: 

  • Electric allows the tank to use solar via the immersion heater. 

  • Electric and Indirect allows solar to be used first, with the boiler as a backup. This option is only available in the Automatic Schedule Control heat source options. See the Schedules and Smart Controls page for more information. 

If solar is your main source but you also rely on a boiler, Electric and Indirect is usually the correct choice. 

Gas and Oil Boilers 

If you have a gas or oil boiler, then select Indirect as your heat source.

This tells the tank to heat using the boiler.  If Indirect is not selected, the tank will not call for heat from the boiler and will rely on the immersion instead. 

If your boiler is broken or temporarily unavailable, select Electric. 

This allows the tank to heat using the immersion heater until the boiler is repaired. Once the boiler is working again, switch back to the appropriate setting for your home. 

Heat Pumps and iHP X Cylinders

If you have an external (outdoor) or integrated (iHP X) heat pump, select Heat Pump. 

The tank will heat using the heat pump’s flow temperature and follow heat-pump-specific behaviour designed to protect efficiency. 

What 'Electric and Indirect' really means 

When you select Electric and Indirect this means your system has two heat sources available. It does not mean they run at the same time.  

  • The tank can use electric (including solar via the immersion)

  • The tank can also use a gas or oil boiler

Mixergy chooses the appropriate source based on availability and settings. 

Will the tank automatically switch between sources? 

The tank will only use the heat sources you allow it to use. It does not guess or switch between systems unless they are enabled in the selected heat source setting. It will select the most efficient source at the time, such as prioritising solar when it is available. 

If you are unsure which heat source is correct for your property, check with your installer, developer, or housing provider before changing this setting.