Water Heaters and Temperature Control
The safety core
The temperature and pressure (T&P) relief valve is the single most tested item. It must be the correct rating for the tank, installed in the designated opening (commonly within the top 6 in of the tank), and never plugged, capped, or valved. Its discharge pipe must be the full size of the valve outlet - no reduction - run by gravity, without traps, and terminate where discharge will not cause injury (commonly 6 in above the floor or outside).
Installation essentials
- Seismic/restraint strapping where required, typically two straps in the upper and lower thirds.
- Drain pan with a drained outlet where leakage would cause damage.
- Combustion air and venting for gas-fired units, with proper clearances to combustibles and correct flue draft.
- Thermal expansion control when a check valve, PRV, or backflow preventer isolates the tank.
- Access and labeling: clear access for service; energy and warning labels intact.
Temperature control
Storage temperatures high enough to control bacteria conflict with scald risk, which is why tempering (mixing) valves are used at the outlet or at point of use. Many codes cap delivered temperature at bathing fixtures at about 120°F; public and institutional occupancies often require stricter limits and master tempering.
Worked example
A tank with a 150 psi / 210°F T&P valve is installed with a 1/2 in discharge pipe on a 3/4 in valve outlet. That reduction is a violation regardless of how short the run is. Replace with full-size pipe terminating safely.
Traps
Plugged or valved T&P discharges; discharge routed uphill; missing expansion tank; and ignoring combustion air in a tight closet.