How Mixergy chooses when to heat
How your heating plan, tariff and safety heating decide when your tank heats.
Your tank’s heating time depends on the heating plan you use. With Mixergy Flex, the tank plans heating automatically. With a manual schedule, you choose the times yourself. Other requests, including safety heating, can still run outside those times.
If you’re getting the hot water you need, use this guide to understand the possible reasons. If you’re running short, follow Tank not heating on a manual schedule instead.
The heating plan comes first
A manual schedule uses the days, heating times and hot water amounts you set. Mixergy Flex is an automatic option that learns your household’s routine and plans heating around it.
To find your current setting, open the Mixergy app and select your tank. Open the menu at the top right, then choose Mixergy Flex. Standard or Economy means automatic heating is active. Off means the tank uses a manual schedule.
A manual schedule is not followed while Mixergy Flex is enabled. See Set schedules and smart control before changing the heating plan.
Why might heating happen at another time?
Cheaper energy periods
Your tariff is the price plan you pay for energy. With supported automatic controls, the tank may use a cheaper period to heat water ahead of when you need it, such as overnight for morning use.
See Set your energy tariff to check the entered prices and times. Don’t change the tariff just to force heating at a particular time.
Helping the grid
At busy times, the electricity grid sometimes asks homes to hold off using power for a while. If your tank is eligible for Mixergy Flex, we’ll know about these requests in advance, so your tank can heat your water beforehand and then pause while the grid needs it. You’ll still have hot water, and your tank earns a reward each time it takes part. That’s what Mixergy Flex is all about!
Not every tank will be eligible, though. It depends on where you live and how your tank is set up, and how much you earn will vary.
Solar electricity
A compatible solar setup can use electricity your panels generate that the home isn’t using. This can cause heating during daylight hours outside your normal schedule.
Solar behaviour depends on the setup. See Is solar PV working with your tank? if you want to check whether solar electricity is reaching it.
An automatic hygiene cycle
The cleansing cycle heats the tank fully to help control Legionella bacteria in stored water. By default, this happens at least once every two weeks. It can run outside normal heating times and take longer than an everyday top-up.
This cycle is separate from ordinary heating. You don’t need to stop it.
Frost protection or a Boost
Frost protection warms the water if its temperature falls below 5°C. It heats to 15°C throughout the tank to help protect against freezing. This is separate from preparing hot water for everyday use.
A Boost is a request for extra hot water. Someone using Boost in the app or pressing the gauge’s up arrow can cause heating outside the schedule.
What should I do next?
- Hot water is available when you need it: a timing change alone does not establish a fault. Keep your normal settings unless you want to change your heating plan.
- You want to choose your own routine: see Set schedules and smart control for manual scheduling. Automatic hygiene and frost protection can still operate outside ordinary schedules.
- The tank repeatedly misses your hot-water needs: follow Tank not heating on a manual schedule. If a schedule has disappeared, follow Schedules disappeared or stopped working.
- None of the explanations fits: note the time heating occurred and take a screenshot if you use the app. Ask Mixergy to check rather than repeatedly changing settings.
Homeowners can contact Mixergy’s Homeowners & Residents team on 01865 595 875, Monday to Friday, 9am to 5pm. If you rent, contact your landlord or housing provider.
[IMAGE – HEATING DECISION DIAGRAM]
Use: Schedule, tariff, Grid Assistance, cleansing and solar feeding into the heating decision.
Caption: Several settings can affect when the tank heats.
Alt text: Diagram showing five factors that influence Mixergy heating times.
Common questions
Why did the tank heat overnight?
It may have used a cheaper period or prepared water for morning use. Check the heating plan and tariff using the linked guides above.
Why did it heat to 100%?
It may be running its automatic cleansing cycle. A full target selected in a schedule or Boost can also request that amount.
Do solar panels always affect heating times?
No. The tank needs a compatible solar setup configured to use spare electricity.
Can a manual schedule prevent all heating at other times?
No. Cleansing and frost protection can still run. A Boost can also request extra heating, and a compatible solar system can use spare electricity outside the manual schedule.
What if the timing change leaves me without enough hot water?
Use Tank not heating on a manual schedule to check what happened. A timing change should not be dismissed if it repeatedly leaves you short.