Component
Temperature and pressure relief valve
The safety valve that discharges water if temperature or pressure exceed its rating. It is tested annually, its discharge pipe must never be capped, and a valve that drips is either doing its job against thermal expansion or failing.
Hot water and scalding
- Water above 49 °C at a tap can scald in seconds, and children and older adults are at most risk. BC's plumbing code limits shower and bathtub water to 49 °C.
- Storage tanks are normally kept hotter (Health Canada advises 60 °C) to limit Legionella growth, with a thermostatic mixing valve tempering the water to the fixtures.
- Never bypass or remove a mixing valve, thermostat or high-limit control to get hotter water.
Official guidance: Government of Canada on water temperature and scalds and HealthLinkBC.
What it protects
A storage tank is a pressure vessel with a heat source. The T&P valve is the last line that opens if the water exceeds the tank's rated pressure or temperature, discharging to an approved location before the tank can fail. Every manufacturer manual and the plumbing code treat the valve and its discharge pipe as safety equipment, not plumbing convenience.
The valve's discharge pipe must run to an approved location, unvalved and uncapped, with its end visible and not submerged: capping the pipe removes the tank's pressure relief entirely.
Drips and tests
Manufacturers call for operating the valve at least once a year to confirm it lifts and reseats. A valve that drips only while the tank heats is usually seeing thermal expansion on a closed system, which an expansion tank absorbs; a valve that runs continuously, or drips when cold, is more likely failed and is replaced.
A valve that has never been tested can seize, which is why the annual exercise is part of the maintenance visit rather than an emergency response.
Frequently asked questions
Why is my relief valve dripping during heating?
Thermal expansion raises pressure as the tank heats on a closed system; the valve lifts and reseats. The fix is an expansion tank sized to the system, not a new valve.
Can I cap the discharge pipe?
Never. The discharge pipe is the relief path and must stay open, unvalved and routed to an approved location.
Request a consultation
CANRO reviews your hot-water demand, equipment and installation constraints. Requests are confirmed by CANRO.
On-site service in Metro Vancouver, BC. Call to check availability.
Sources and verification
- CANRO Heating & Cooling — About · Canadian source · accessed September 7, 2026
- Bradford White Installation and Operation Manual (T&P valve) · 238-51012-00V · accessed September 7, 2026
Facts checked September 7, 2026. Last updated September 7, 2026. Technical reviewer: not yet assigned.