Ariston Pressure Relief Valve Leaking

The Short Answer: An Ariston T&P that drips is doing its job: pressure or temperature is over the setpoint, usually 150 psi / 210°F. Small Andris / Velis tanks have nowhere to expand on a closed PRV system. Do not cap it. Gauge a hose bib. A stream is shut the cold inlet, kill power, call a licensed plumber. Bottom-shell drips are a different page.

Search Intent & The Real Problem

You found a wet discharge on an Andris under the sink, a Velis or Pro1 on the wall, or a Fast/Aures tankless. Hot water still works, so it feels minor. It is not. That valve is the last mechanical fuse between thermal expansion in a 10–30 gallon vessel and a scalding vanity. Homeowners mix this up with a bottom leak or a front-cover weep. Bottom puddle with fittings dry: Ariston from the bottom. Wet front cavity: front panel. No hot water: Ariston no hot. Generic new-heater T&P: T&P on a new unit. Tankless cousin: Rinnai T&P.

What other guides get wrong

They start with “defective Ariston valve, warranty it.” I have thrown away good factory valves because nobody gauged the hose bib. They skip expansion on a condo that just got a PRV or a check at the meter — a 15-gallon Andris will lift a 150 psi valve faster than a 50-gallon. They put pipe dope on the discharge outlet or hang a tube so it holds the lever up. They tell you to test the lever weekly on a wall-hung Velis over a finished cabinet. And they still say cap it overnight.

Step-by-Step Troubleshooting

Step 1: Confirm it is the T&P — not a bottom fitting or the tank

• What to look for: Dry the valve body, the tank threads, and the discharge opening separately. Wait two minutes. A thread weep stays at the bushing. Discharge water means the valve lifted. Some Ariston point-of-use tanks use a 1/2” relief, not the 3/4” you see on a 50-gallon — match the outlet size. Never reduce it.
• Required tools: Paper towel, flashlight, phone camera.

Step 2: Kill energy if it is streaming, then gauge the house

• What to look for: A hard stream: cold inlet off, unplug or breaker off — apartment shutoff. A slow drip: you may gauge first. Static at a hose bib over ~80 psi. These little tanks are often rated to 150 psi maximum; many T&P valves open at 150 psi / 210°F. City pressure plus a failed or missing PRV will make a healthy valve drip every heat cycle.
• Required tools: $12 hose-bib gauge. Breaker lock if you are draining.

Andris 120 V ~1440 W is not a 4500 W / 240 V ~18.8 A house tank — still prove it dead before covers. Do not restore power to an empty vessel.

Step 3: Expansion — small tanks punish closed systems

• What to look for: Check valve or PRV on the city line, no expansion tank, or a tank whose Schrader spits water — expansion full. Closed systems have nowhere for heated water to go. The T&P becomes the expansion tank. A 10-gallon Andris rises in pressure faster than a 50-gallon because the same heat has less volume to expand into. Precharge should match static house pressure, typically 50–60 psi, with the expansion tank isolated and drained.
• Required tools: Tire gauge, isolation valve on the expansion tank.

Day-one weep on a brand-new Ariston is this, not a dead shell — new heater, water in pan. Overflow that will not quit: overflow discharging.

Step 4: Seat damage, test lever, and overheat

• What to look for: Someone lifted the test lever “to see” and the valve never reseated — after testing. Scale or solder chips on the seat from the install. Thermostat runaway so the tank actually hit the temperature limit — reset, reset loops if an ECO is in play. Tankless Fast/Aures: scale-driven overshoot lifts the relief the same way a Rinnai does. Replacement without fixing pressure is a callback in 48 hours.
• Required tools: Eyes on the lever (it must sit fully down). Thermometer at the outlet. Do not keep cycling a streaming valve.

A valve that will not close is stuck open. A valve you just swapped that still weeps is leaking after replacement — the house is still over-pressure.

Step 5: Only then replace the valve — match the Ariston port

• What to look for: Same pressure and temperature stamp, same thread, discharge the full outlet size, slope to a visible drain, no threads on the outlet in UPC/IPC language. Wall-hung Velis: support the vessel; do not hang a full tank off a 1/2” relief while you wrench it. If the tank bushing spins, stop. That is a heater, not a valve. Wet foam after every fitting is dry is a shell — do not epoxy it.
• Required tools: Two wrenches with a backup on the tank, potable PTFE or a new gasket, bucket. No floor drain? This drain procedure.

Gas tankless: leave the gas cock alone. Do not purge fittings.

When DIY Ends: Calling a Licensed Pro

Stop if the valve dumps a hard stream, the vanity is flooded near line voltage, you smell gas, incoming pressure is over 80 psi and you do not have a PRV, or the bushing turns with the valve. You may gauge a hose bib, photograph the wet part, and isolate water. Capping the T&P, reducing the discharge, or “just snugging it” are how point-of-use tanks become incident reports. A licensed plumber will set or replace the PRV, charge or add an expansion tank, and only then swap a matching Ariston-port T&P.

Frequently Asked Questions

Q: Why is my Ariston pressure relief valve leaking? A: House pressure over about 80 psi, no room for expansion in a small tank, a dirty or tested seat, or actual overheat. Discharge water means the valve opened. A wet jacket is not this page.

Q: Can I cap a dripping Ariston T&P overnight? A: No. A capped relief is a code violation and a scald/rupture risk. Close the cold inlet and shut the heater down instead.

Q: Does a small Andris need an expansion tank? A: On a closed system (PRV or check at the meter), yes — more urgently than a 50-gallon, because there is less volume to absorb the heat cycle. Replacing the T&P without expansion is a 48-hour callback.