1. How cold is the incoming water?
If not mistaken this unit is 3.6 kilowatt of heating only. If the incoming water temperature is below 24°C it will only produce luke warm water even already turn the knob to maximum.

2. There are still spare parts for this model but for your piece of mind you should buy a new instant water heater for your parents. Panasonic is a good choice.

But do check the temperature of their incoming water supply 1st, cos already 2 consecutive days my place also has been raining, so my heater also unable to be hotter than usual.

FYI Panasonic do sell a 4.8 kilowatt units for those staying in Cameron Highlands and Genting Highlands.