Instant water heater despite gas central heating?

Hello everyone,

I have an old multi-family house in which, due to a tenant change, an apartment is now vacant. The apartment was rented for over 20 years, so I had no access. It has now come to my attention that there is a flow heater in the bathroom, even though there is a gas central heating system (which is also responsible for hot water supply). Each apartment also has its own hot water meter, so I am surprised that a flow heater is installed in the apartment, which also turns on when water is running in the bathroom. Does anyone have an idea why, in addition to hot water preparation via the central heating, a flow heater would also be installed? I would like to have this clarified before I rent out the apartment again.
Best regards

Does any of you have an idea why an instantaneous water heater is installed in addition to hot water preparation via the central heating? I would like to have this clarified before I rent out the apartment again.

Could be a thousand reasons. Remaining, renovation with piping of hot water not possible, bathroom installed afterwards, hot water pipe to the apartment is clogged, etc.

It may also have taken the tenant too long for WW to arrive or it is (with a long sporadically used pipe) a measure against Legionella (not that it couldn't be solved differently).

That is not uncommon. The apartment I lived in at the time and all the kitchens above and below were far from the central WW, so all the kitchens were equipped with a [Durchlauferhitzer]. That was also planned that way. Other reasons have already been mentioned.