Hi for leaking case, only the following 2 cases can be repaired :
i) Gasket leaks or
ii) Inlet / outlet pipe leaks.

Leaking from any part of the body ( Stainless Steel tank ) is beyond repair at site. Of cause if you insist to repair, it is
possible but you need to dismantle, bring down the heater, send to factory, do pressure test, re welding if can detect the leaks,
pressure test again after welding and reinstall water heater back. It is so much hassle and Not worth the efforts. That is why
people dont repair it.

Normally a PRV ( pressure release valve ) will be installed at the inlet pipe to prevent over pressured/ over heated inside the
Water tank, thus avoid unwanted explosion. ( tho cases of explosion is only 0.0001 % ! )
For bigger tank, some install TPV ( temperature pressure release valve ) at the outlet pipe. Double protection, this is the safest way.

rdgs.

The model you mentioned is an air cond heater, water will only be heated up after you turn on the air con unit.

This model is Not really popular because of the efficiency and also not many technician know how to repair this.

rgds.