(310) 628-9399

Szeto Plumbing · San Gabriel Valley

A dripping T&P relief valve

The temperature and pressure relief valve protects your tank.

Call or text for a quoteText a photo

Mon–Sat 8:30 AM–7 PM · San Gabriel Valley

Mon–Sat, 8:30 AM–7 PM

Call or text (310) 628-9399

Kitchens, baths, heaters, main lines

Updated · 3 min read

Short answer

The temperature and pressure (T&P) relief valve opens to protect the tank from too much heat or pressure. If it drips, check house water pressure and whether you need an expansion tank before blaming the valve. Replace it if it keeps leaking at normal pressure.

On this page
  1. What the T&P valve does
  2. Why it drips
  3. Thermal expansion and closed systems
  4. Testing and replacing
  5. Common questions

What the T&P valve does

Every tank water heater has a relief valve near the top, with a pipe running down to near the floor or outside. It opens if the tank gets too hot or the pressure climbs too high.

It is a safety device. It should never be capped, plugged or removed.

Heat raises pressure then Pressure reaches valve rating then Valve opens then Water discharges then Tank stays safe1Heat raises pressure2Pressure reaches valve rating3Valve opens4Water discharges5Tank stays safe
How a T&P valve protects the tank.

Why it drips

Thermal expansion and closed systems

Water expands when heated. If a pressure regulator or check valve stops it from pushing back into the street main, pressure spikes in the tank every heating cycle.

An expansion tank on the cold line absorbs that extra volume. It is often needed once a regulator is installed.

Valve problem: Drips at normal pressure; Debris in the seat; Replace the valve. System problem: Drips after heating cycles; High house pressure; Add expansion tank or PRVValve problem• Drips at normal pressure• Debris in the seat• Replace the valveSystem problem• Drips after heating cycles• High house pressure• Add expansion tank or PRV
Is it the valve or the plumbing around it?

Testing and replacing

Testing involves lifting the valve's lever briefly to let water flow. Older valves that have not been opened in years sometimes do not reseat afterward.

Replacing the valve means shutting off water and the burner, draining some water, and threading in a new valve with the correct pressure and temperature rating.

Common questions

Is it safe to keep using a heater with a dripping T&P valve?

The tank is still protected, but find the cause soon. Never plug the discharge pipe.

Where should the discharge pipe end?

It should run to a safe spot near the floor or outside, with no valve or cap on the end.

Can water hardness affect the T&P valve?

Yes. Scale can keep the seat from closing fully, which is common in hard-water areas.