My reaction to the apparent problem is to fit a shower which uses the stored hot water.
Electric showers do not give a very good shower, usually no more than 6 litres per minute. Whereas a cylinder can give up to 22 litres per minute. I like at least 10 to 12 litres per minute for a nice shower.
Then there is the question of the cost! It is very common with a stored hot water heating to have it reheated overnight at a reduced off peak electricity price.
The smallest cylinder is usually about 100 litres which will give a 10 li/min shower for 10 minutes and will reheat in about 90 minutes.
I cannot guess at how many people live there and why their hot water consumption is apparently so high. A 6 minute shower is totally adequate for most people's hygine needs. Longer is just profligate.
It would not be very expensive to fit a 48 Amp changeover relay to change the supply from underfloor heating to shower with a simple switch to power it when the shower is needed. Certainly far cheaper than any increase in capacity to the flat which could easily be several hundred pounds.
We see quite a lot of this, and I think the list of "Similar Threads" at the bottom of each page of messages (seemingly without any regard for the age of those threads) probably has a lot to answer for!
Yes, realised it was old when I saw @ban-all-sheds answer, I was surprised when we bought this house, 60 amp supply, two kitchens, three bathrooms with as a result two electric showers, but never blown the fuse. Think unlikely as basic two homes, main house and granny flat, and granny flat only used for visitors.
But note
2008 so just into 17th edition, and below that 2005, power shower. What sometimes worries me, is valid answers when 16th edition was in force, are no longer valid.
We see quite a lot of this, and I think the list of "Similar Threads" at the bottom of each page of messages (seemingly without any regard for the age of those threads) probably has a lot to answer for!
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