[porphyra]

Sounds like you're using a totally different type of water heater (tankless) and not a heat pump water heater (which has a tank, so even if the fuse pops, the water won't get cold instantly).

[Balgair]

Nah, same type. The tank was about half the size of a normal one. The water didn't get cold, just not as hot as I'd liked it to be.