Water Heaters, Temperature Control, and Thermal Expansion
Water Heater Installation
Water heaters require proper clearances, combustion air (for fuel-fired units), seismic strapping where required, and a temperature and pressure relief (T&P) valve. The T&P discharge must terminate safely, typically to a drain or exterior, and must not be capped or reduced. Questions test relief valve piping, drain pan requirements, and clearance to combustibles.
Temperature Control
Scald prevention is a major theme. Shower valves must be pressure-balancing or thermostatic, and hot water delivery temperature may be limited. Questions test the difference between the thermostat setting and the delivered temperature, and the role of mixing valves.
Thermal Expansion
Closed systems with a backflow preventer or check valve need thermal expansion control, usually a thermal expansion tank. Without it, pressure spikes can damage the system. Questions test when an expansion tank is required and where it is installed.
Rule of Thumb
If a water heater is on a closed system (backflow preventer or check valve), it needs an expansion tank. If a question describes a relief valve discharging or a capped relief line, the answer is to restore proper discharge piping.
Worked Example
A new water heater is installed with a backflow preventer on the supply. Pressure spikes trip the T&P valve. The fix is a properly sized thermal expansion tank on the cold side.