Also if the coil was split would the water in the hot water tank be dirty? As it was relatively clean.Ok then it’s impossible to tell from the angle of your pics the levels. That will be down to you. As long as the water in the f&e is lower than that in the larger tanks then you can rule out split coil. Only logical other fault then would be one of your mixers passing
Can the mixers pass if they are off? As this has happened overnight so nothing on.
Thanks again.