The situation

Illustrative example. Not a real job or customer.

A homeowner notices the relief-valve discharge pipe on the garage tank drips for a few minutes after morning showers, then stops. Faucets around the house also seem to spray hard.

  1. They move stored items away from the discharge outlet and keep children clear
  2. They resist the temptation to cap the pipe
  3. They note in a log that drips follow heavy hot water use
  4. They ask a licensed plumber to check pressure and expansion, not just the valve

In this example, the plumber found high incoming pressure and no way for heated water to expand, so the valve was doing its job.

How the cause was narrowed down

  • IfDrip only after the heater runsSuggests thermal expansion in a closed system.
  • IfForceful flow at all fixturesSuggests high incoming pressure; checked with a gauge at a hose bib.
  • IfSteady drip regardless of useWould have suggested a worn valve instead.
  • IfScalding water at tapsWould have pointed to a thermostat problem.

What was discussed, in this example

  1. Measure pressure.A gauge reading showed higher pressure than the plumber recommended for the house.
  2. Look at the regulator.The pressure regulator at the water service entry was checked.
  3. Handle expansion.Options to manage thermal expansion were explained. Whether a specific device is required was left to the city's rules.
  4. Test the valve.The relief valve was checked and the discharge pipe routing confirmed safe.

Why swapping the valve alone would not have worked

A new relief valve in the same conditions would have dripped just like the old one, because it would have been opening for the same reason. Fixing the pressure and expansion is what stopped the drips.

High pressure also strains other fixtures and connectors in the house, so dealing with it helped beyond the water heater.

Terms used

Closed system
Plumbing where water cannot flow back toward the supply, often because of a check valve or regulator.
Thermal expansion
Heated water takes up more space, raising pressure in a closed system.
Hose bib gauge
A simple pressure gauge that threads onto an outdoor faucet.

Common questions

Is this a real case?
No. It is an invented example illustrating a common cause of relief-valve drips.
Can I cap a dripping relief pipe?
Never. The pipe is the outlet for a safety device. Capping it removes the protection.
Is an expansion tank required in Fullerton?
Requirements depend on the plumbing and local rules. Check with the city and ask your plumber.

General information for Fullerton, not a quote or professional advice. In an emergency, call 911.