ᐅ How do temperature fluctuations occur in a domestic hot water system?

Hello,
I hope this is the right forum.

Can someone explain to me how temperature fluctuations can occur in domestic hot water?
The domestic hot water is set to 60°C (140°F). The circulation is at 55°C (131°F).
It receives water from the buffer tank at 65°C (149°F) (limited by a mixing valve), which operates at around 70°C (158°F).
At the apartment outlet, the domestic hot water is delivered at a consistent 60°C (140°F).
However, sometimes the hot water temperature seems to fluctuate slightly while showering.
It’s not constant as it was set at the single-lever mixer.
How can this phenomenon be explained or fixed?
Could it be because when many users demand hot water at the same time, the domestic hot water does not reach 60°C (140°F)?
Or could it be that the demand at that time is actually too low?

Thank you.

Spontaneous fluctuations in the single-lever mixer most likely result from pressure variations in the hot or cold water supply line.

Pressure variation == flow rate at the mixer changes == final temperature changes

Domski schrieb:

Spontaneous fluctuations in the single-lever mixer are most likely caused by pressure variations in the hot or cold water supply line.

Pressure variation == flow rate at the mixer changes == final temperature changes

Thank you. But where do these pressure variations come from? We hardly ever had this problem before.

What does "before" mean?

Cause: toilet flush, dishwasher, ... (anything with a solenoid valve), possibly other taps if the pipe diameters are narrowly sized

The only reasonable explanation has already been given to you by @Domski. The pressure fluctuates, often caused by someone else using water, for example flushing a toilet. Fluctuations in the primary supply network, meaning from the utility provider, are also possible. And what does it mean that the problem didn’t exist “before”? What was different before?

Domski schrieb:

What do you mean by "before"?

Cause: toilet flush, dishwasher, ... (anything with a solenoid valve), possibly other outlets if the pipe diameters are undersized

Alright. So these fluctuations are not due to insufficient temperatures in the buffer tank. I had thought that producing domestic hot water at around 60°C (140°F) with 65°C (149°F) wouldn’t be enough, causing these fluctuations.

I would have expected the domestic hot water temperature to drop by about 2°C (4°F) or the buffer supply temperature to rise by about 2°C (4°F)…