Comment by shmoozername

Looks to me like he maintained proper mains separation except for the one assembly mistake he admitted to (which wasn't catastrophic, obviously -- his wiring color choices look good for avoiding catastrophic errors). The relay board he's using (I recognize it) is rated for mains voltages, and power-wise is ok-ish for the task (I wouldn't choose it for a commercial product, but for his exact scenario--see below--it's probably ok). Doubling up the relays works fine for the main concern, which is overheating via sustained high amperage, which is how fires start. Surge risk is usually just welding the relay, not starting a fire (unless you're way over spec, which he is not), and it almost always welds shut, not open, so less likely to fail silently into the scenario where it's running on one relay and the sustained amperage becomes a risk, and instead into behaving obviously badly as is typical when motherboards go out (at which point you turn it off and rectify, just like a commercial one). He mentions the whole unit is isolated from mains when not in use, so in that respect it's safer than a commercial one as long as he doesn't run it when away from home/asleep.

Again, not a viable commercial design, but not insane with proper supervision either.

I was curious how you knew about the leak sensor so I did a quick search, and see you're just making things up to complain about -- that model has a turbidity sensor (which I suspect are the NC wires you noticed), but no leak sensor. Oh no! His water might be too turbid! Also the fill valve is wired inline with the float switch (in the machine itself), so it's double-covered for overflow prevention. Flooding seems highly unlikely.

The flaky connections he mentions are the 3 volt ones -- again, not a fire risk. Common for low-voltage contacts like that to get flaky in commercial devices too (e.g., face-plate contacts for thermostats, etc) and without disastrous outcomes. The high-voltage/amperage connections he uses are plugged into the OEM harness, so the same connectors as the OEM motherboard. So, again, seems like you're just making up things to complain about.

I don't want to encourage people to mess with mains power if they're not adequately informed, but it's also not a magical domain you can't learn about with a little research and caution (easier in the US than the UK...). And his gadget worked for years, by the sounds of it, which is better than any commercial appliance I've bought in the last decade...

But I agree he's probably gambling on the home insurance issue, even if his device(s) isn't at fault...