We have a storage water heater (2kW) and I believe it will work well with a timer, and just heating during the night when the power is less expensive. (The power company has automatic reading of the meter every single hour) The power is less ekspensive from midnight to about 6 a.m.
I want to build a unit controlled by a clock and an extra thermo-relay to override the clock if the temperature falls to much.

I know this is more or less common in the USA so your experience is important for my project here in Norway. Pretty much are equal, the system here is nominal 230V yours are 240, it is single phase, and the frequency does not matter as long as I do not use a timer with a frequency depended motor.

I do not trust regular timer with a mechanical switch even when it is rated for 16A so does a solid state relay or a mechanical industrial relay be the most trust-able?
Or what would you use in your house if you should build it and not buy it?
Should I put in more functions? what and why?