Not high enough temperature although thermostat has been changed

Dear Sir/ Madam

Please help me out from the hot water problems

(Pulsacoil 2000)
I'm expriencing that warm water is coming out from the shower for the first person (10~15min shower time). **Warm water means not hot but it is warm (not enough warm). But for the second person, there is lukewarm water is coming mostly. **Lukewarm means it is much colder than warm water as the mentioned above.
Recently (last week), plumber changed thermostat, it got a little better than before but I would like to say it is same still.

Please give me an advice what do I have to do step by step

Thanks

Pulsacoil 2000
What size unit?
You will only get so much hot water from the unit. May have to boost for more.

Is the unit hot?
Feel the big pipe coming out of the top of the unit.
If you can hold it for very long then unit not hot enough.
Remember it is a thermal store. It stores heat.
Your hot water does not come from the unit.
But goes through a plate heat exchanger in the unit. The unit water stays there until it is ever drained out for work then refilled.

The unit needs to be on at least E7 every night to work.

Mike