[Mark_K]

[ QUOTE ]
water puddle in the basement, kinda big
almost certainly came from the safety blowdown of the hot water heater
what would cause this?

ldo high pressure

but why would it have built up high pressure all of a sudden?
thats the puzzle
somebody smart please tell me

[/ QUOTE ]

Two ideas:
1. Water hammer... Either air in the pipes, has your water been turned off recently? Or some appliance that turns the water off fast (e.g. like a dishwasher)

Or

2. Old water heater with faulty thermostat. The water heater thermostat didn't turn off, water boiled, safety fired...