Water pump
Either under the bed or kitchen sink. May be a panel screwed to the floor under the sink concealing the pump. Might be under the bed under the screwed down side. It will be in a fairly accessible location.
Blank interior panels with screws showing are access doors to system service Points. Relays, fuses and junction boxes on the electrical system, furnace, water faucets, pump and water heater.
The bypass valve is between the hot (red) and cold (blue) line to the water heater. Where the water heater is on the outside the access is on the inside.
Sometimes drawers need to be removed to get to something.
__________________
|