Using a heat pump
How your tank works with a heat pump and why heating can take longer.
A heat pump uses electricity to collect warmth and transfer it into your heating and hot water. It normally heats water more gradually than a boiler or the tank’s direct electric heater, so longer heating times can be normal.
Your installer should set up the tank and heat pump to work together. This article explains what you are likely to notice and what to check before asking for help.
Check how the tank is set to heat
This article covers a Mixergy tank connected to an external heat pump. If you have a Mixergy iHP X, its heat pump is built into the tank and its product guidance applies instead.
The installer should select Heat Pump when an external heat pump heats your hot water. To view the setting, open the Mixergy app, select your tank and choose Heat Source in the main menu. If you use automatic Mixergy Flex heating, its settings also specify the source used for automatic schedules.
Do not change this setting to make heating faster. The wrong option can increase costs or stop the system working as designed. Ask the installer, landlord or housing provider if you are unsure.
What should I expect while it heats?
An external heat pump normally warms the water throughout the tank in a longer cycle. It will still show heating by the 10% percent increments, but the full tank is heating. This is dfferent from direct electric which can prepare only a small section at the top. An immersion heater is the electric heating element inside the tank.
The gauge is the slim black panel with lights and buttons on the tank. Its red lights show how much hot water is ready. They can change slowly during a heat-pump cycle, even though the water is warming.
Fewer than ten red lights can still be enough for your household. The important check is whether you have the hot water you need at the expected time.
Do not compare heat-pump heating time directly with a boiler or immersion heater. What matters is whether enough hot water is ready when your household needs it.
How does Boost work with a heat pump?
Boost is a request to heat extra water. On the gauge, press the Boost Up button marked with an up arrow. Green lights show the additional amount requested; they turn red when that water is ready.
With Heat Pump selected, the request starts or continues a hot-water cycle when the heat pump’s controls allow it. See Set hot water levels and use Boost if you prefer to use the app.
Do not switch to electric heating unless the installer has set it up as an approved backup and has told you when to use it.
Why might heating pause or stop before the target?
The heat pump controls when and how it runs. Heating can pause because:
- Space heating has priority.
- The heat pump has reached its normal flow-temperature limit.
- The system is adjusting its operation to use energy efficiently.
- An installer setting limits the hot-water cycle.
- The heat pump is showing a fault or waiting condition.
Flow temperature means the temperature of the water leaving the heat pump and travelling towards the tank.
If heating repeatedly stops at the same level or Boost makes no progress, check the heat pump’s own display. Record any message, then contact the installer or housing provider.
What happens during the cleansing cycle?
The cleansing cycle periodically heats the tank fully to help control Legionella bacteria in stored water. A heat pump works at lower temperatures, so completing this cycle can take longer. See Why does your tank heat to full every two weeks? for the explanation.
Depending on the installation, the system may try again or use an approved immersion heater to reach the required temperature.
Do not disable the cleansing cycle or other water hygiene protection.
When should I ask for help?
Contact the installer or housing provider if the heat pump shows a fault, heating repeatedly stops, Boost never progresses or you regularly do not have enough hot water.
[IMAGE – HEAT-PUMP HEATING]
Use: Simple comparison of gradual whole-store heat-pump heating and direct electric heating.
Caption: A heat pump normally warms the store gradually through a longer cycle.
Alt text: Diagram comparing gradual heat-pump heating with faster direct electric heating.
Common questions
Does a heat pump heat only the top of the tank?
No. An external heat pump normally heats the whole store through the connected system.
Why is Boost taking so long?
Heat pumps use longer, lower-temperature cycles. Check that the hot-water level is rising before deciding that Boost has failed.
Why is the immersion heater running?
It may be providing approved backup or helping the tank complete its cleansing cycle. Ask the installer if it runs often and you do not know why.
Can I still use the gauge?
Yes. You can check the hot-water level and request more hot water from the gauge. The response will still depend on how the heat pump has been configured.
Why is space heating working but the hot water is not?
The system may be giving space heating priority, or a hot-water setting may need checking. Look for a message on the heat pump and contact the installer if the problem continues.