Pana DH-3MP1/DH-3MP2 (with pump & push start)

M series is tried and true workhorse. N series leh..my advise better buy M series, cheaper n more reliable due to lesser cost cutting.

Its the internal organs' reliability that matter.

I use the non pump DH-3MS1 for few years and works like a charm. LCD screen got the same old lifespan issue after 8-10 years (I'm sure u have seen digital watch, old monitors, calculator screens they turn purple or black "bruises" and then you need to fuss with fixing it via the polarizer film or the reflective backing film to get it working -- too much hassle)..

Generally we used many Pana series but as you can see above..

How to tell M or N
https://www.panasonic.com/my/consumer/home-...ome-shower.html
The rose gold stuff is N series
The black and white workhorse model is M series
Not a bro sis here.
Without LCD lesser long term problem. Generally Pana WH no problem but (see above case by our forumer) was from N series.. hence i still would recommend the more boring M series type, this one many friends n neighbour using all OK.

Generally WH does wear out over time.. but most importantly is that you can use a cheap heater but MUST have 10mA RCD fitted + proper installation.

Typically WH can last a decade or more.. some even since 1997 after 15 years tank health will be affected by corrosion and your old hose/shower head also clogged with limescale. One new push start WH only costs from 280-400 so its only like 28-40 bucks a year if you divide by 10 years.

Without that 10mA RCD.. every year or two people sayonara https://www.st.gov.my/en/contents/presentat...er%20Heater.pdf
those cases in the ST PDF don't have 10mA (0.01A) WH-specific circuit RCD installed.

As the whole house one is likely fitted with 100mA (0.1A).. or 300mA (0.3A) (higher mA leakage tolerance = close more eyes), effectively in practice not many older homes have a sensitive (and "safe for school use") 30mA (0.03A) whole house RCD in the DB box, so those 100/300mA whole house RCD is the only safety (which is technically useless like an airbag that deploy 3 mins after accident).

I have retrofitted 10mA (0.01A) WH-specific circuit RCD to be safe for my old 1997 heater, but it may require pulling a new dedicated LNE power line from DB box as that 10mA is super sensitive and cannot operate on shared neutral.

Yes, for Pana (and Hitachi) push start models, [the water flow + heater activation] is controlled together by the big push switch.
Shutting off the water only at the inlet valve / built-into-the-wall valve will also turn it off (in a CRUDE method similar to the factory production line big red button) as the flow sensor (to avoid dry burn like what Selene mentioned) will trip off the heaterbut it is not the proper way lah. Proper way, use the push on/off big push switch. 

WH is exposed and easy to fix or change new one. The built-into-the-wall stuff should be used as minimal as possible, if the valve wear out then you might need to hack to replace it.

Hello, how's your N series water heater?

You chose the non pump or pump version?