The situation

Illustrative example. Not a real job or customer.

A homeowner in a Coyote Hills house with a regulator notices a small puddle under the water heater's relief valve discharge pipe a few mornings a week. An afternoon gauge reading looks normal.

  1. They leave a gauge with a high-reading needle on the hose bib overnight.
  2. By morning the needle shows a peak far above the afternoon reading.
  3. The rise happens on nights after showers and laundry, not on quiet nights.

The pattern ties the pressure spike to the water heater running, which points toward thermal expansion.

Separating the suspects

  • IfPressure rises whether or not hot water was usedThenSuspect the regulator leaking street pressure through.
  • IfPressure rises mainly after the heater runsThenSuspect thermal expansion in a closed system.
  • IfNo expansion tank is presentThenExpansion has nowhere to go.
  • IfA tank is present but sounds solid when tappedThenIt may be waterlogged and no longer working.

What the plumber checks in this example

  1. Tap test.The existing expansion tank sounds solid from top to bottom.
  2. Air valve.Pressing the valve core on the tank's air side releases water, not air, showing the bladder has failed.
  3. Regulator.The regulator holds its setting with the heater off, ruling it out.
  4. Relief valve.The valve shows some scale; after repeated discharges, replacement is suggested along with the tank.

Outcome

In this invented case, a correctly sized tank with its pre-charge matched to house pressure replaces the failed one, and the relief valve is replaced. The seismic straps are checked while the plumber is there. Over the next week, the overnight needle stays close to the afternoon reading, and the puddle does not return.

The owners add the tank check to their yearly list, since a tank can lose its charge again over time.

Takeaways

Common questions

Is this a real case?

No. It is an invented example.

Can a regulator and expansion tank both fail?

Yes, which is why checking each one separately matters.

Is a dripping relief valve dangerous?

The valve is doing its job, but the cause should be found promptly. Never cap or plug it.

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