Just wanted to add that I decided on the 8kw model but then found that the two places who said they had it were bullshitting and the options were a different brand or the 6kw which is not enough or the 10kw and a higher system spec. No contest really.

Goes on the inlet side.

Someday you will need to start trusting us.

Having been in contact with those more knowledgeable in these matters.

The 30A is unlikely to open at 45A in the 10 mins or so the heater will be operating (particularly if you don't run it at full whack). If you can't souce a 50A the 40A will likely do the job just fine (it's there to protect the cable).

You DO need an RCD, either just on the heater or (better) covering the whole installation.

it appears to be a sealed system (Unvented) water heater that incorporates a pressure relief valve. That's good so far.............BUT..........should the system over pressurise I see no way of discharging safely. If that "safety" valve operates, anyone in the vicinity could be scalded by super pressurised steam. The discharge should be carried away by additional pipeworkto where it can drain safely.

I should add, that if the thermostat has a fail to safe ie thermal cut out, the above problem is unlikely. I think it was about 10 years ago that there were new regs in UK re thermostats on water heaters. Before that if the thermostat failed, the water boiled and this would cause the pressure relief valve to vent scalding steam. Make sure that the pressure relief valve is on the inlet not the outlet as any venting will be cooler water.

Also stop valves go on the inlet side.