Is the thermostat making the T&P valve leak?
Fixable — and free, if this is the cause
The T&P valve opens on temperature as well as pressure, at about 210 °F. A thermostat set high enough to approach that will open it. This is the one cause with a free fix: turn the dial down to 120 °F.
Do not open an electric heater's thermostat access panel without switching off its breaker first — the terminals behind it are live at 240 V.
How to tell it's this
- Hot water scalds at the tap rather than running merely hot.
- The dial is set above 130 °F, or at a vague "A / B / C" mark near the top of its range.
- The drip gets worse after a long heating cycle and eases off later.
- Steam or very hot water comes from the discharge pipe, not cold-ish water.
What to do
- Set the thermostat to 120 °F. On an electric unit there are usually two thermostats behind the access panels and both need setting to the same figure.
- 120 °F is the US Department of Energy recommendation. It also cuts standby energy use and is the standard scald precaution for children and older adults.
- Give it a full day. The tank holds a lot of heat and will keep dripping while it cools.
- If it still drips after 24 hours at 120 °F, the thermostat is not your cause — work through the other three.
What it costs
Turning the dial costs nothing. If the thermostat will not hold the setting it needs replacing, which is a plumber or electrician visit rather than a DIY job on a live panel.
Typical US ranges for 2026, not quotes. Labour is 30–50% of an installed price, so where you live moves these numbers more than anything else does. Get two or three local estimates.
If that's not it
The water is not especially hot and the dial is already at 120 °F
The valve itself has failed →
It only drips while the heater is actively running
Thermal expansion on a closed system →
Not sure which of these it is?
Answer four questions — where it's leaking, tank or tankless, gas or electric, and how
old it is — for a specific cause, a repair-or-replace call, and a cost.