As this is the uk the temp could have dropped very quickly but does seem odd, maybe the tank was in a cold garage?
I think every tank should have 2 heaters, I run 3 but have one about 3 degrees lower so it only comes on if one fails. I also have all 3 on different plug bars in case a fuse goes.
I I built a house now I would have at least 3 different circuits for the tank
I think every tank should have 2 heaters, I run 3 but have one about 3 degrees lower so it only comes on if one fails. I also have all 3 on different plug bars in case a fuse goes.
I I built a house now I would have at least 3 different circuits for the tank