The reason can typically be explained by the Havenwise optimisation algorithms.
Havenwise will ensure your hot water cylinder is heated up in advance of the setpoint you set in the Havenwise app.
The timing for hot water cycles can vary, because Havenwise selects the cheapest moment to activate the hot water cycle. Sometimes it might feel counter intuitive, but there are 2 main factors that Havenwise tries to optimise for under the hood:
Your electricity tariff. If you are on a time of use tariff, Havenwise aims to make use of the low price periods in your tariff.
Outdoor temperature. A 1°C higher outside temperature means a 2-3% higher efficiency. So Havenwise selects the warmest moments ahead of your setpoint.
These 2 factors are continuously monitored together.
An example to make this concrete
Let’s take an example of a user with a 6am hot water setpoint in the Havenwise app, and a tariff with cheap overnight electricity.
It’s possible that some days, the hot water cycle runs at midnight because the outdoor temperature at midnight is projected to be 2-3°C higher than the outdoor temperature at 5am. A 3°C difference in outdoor temperature means a 6-9% difference in efficiency of the heat pump!
But there will be days where the outdoor temperature has a different pattern, and it will be warmer at 5am than at midnight. For those days, the hot water cycle will activate closer to 5-6am.
Pretty smart!
It’s also important to understand that Havenwise will only activate a hot water cycle when it’s needed
If we see that your hot water cylinder temperature is close to the setpoint, your heat pump won’t be activated to raise the temperature by a few degrees.
The reason is simple: hot water cycles to raise the temperature by only a few degrees are inefficient. In addition, the cylinder typically contains more hot water than you think, because the cylinder temperature is measured at the bottom of the cylinder, whereas the hot water in the tank raises to the top.