Why is my water heater relief valve leaking?
The temperature-and-pressure (T&P) relief valve is one of the most important safety devices on your water heater. Its job is to release water if the pressure or temperature inside the tank climbs to dangerous levels, preventing a catastrophic failure. So when it starts leaking, it is worth understanding why.
A leaking relief valve is not always a fault – sometimes it means the valve is doing exactly what it should because there is a real pressure problem to solve. Other times the valve itself is simply worn out.
HeatLand serves Metro Vancouver and the Fraser Valley, and below we explain the causes, why you must never cap this valve, and when to call a licensed technician.
It May Be Releasing Genuine Excess Pressure
The most important thing to understand: a leaking T&P valve may be doing its job. If pressure or temperature inside the tank is too high, the valve opens to release it. This is a safety response, not a defect.
The usual driver is thermal expansion. As water heats, it expands, and in a closed plumbing system that has nowhere to go, pressure rises. Many homes use an expansion tank to absorb this; if that expansion tank has failed or was never installed, pressure can spike every heating cycle and force the relief valve to weep.
High incoming water pressure from the municipal supply, or a temperature setting that is too high, can also trigger it. Because these are system issues rather than valve issues, simply swapping the valve will not fix the leak – the root cause must be diagnosed and corrected by a licensed technician.
Or the Valve Itself Is Worn Out
The second common cause is a failed valve. T&P valves have an internal seat and spring that can wear, collect mineral debris, or degrade with age. Once the seal is compromised, the valve may drip continuously even when pressure and temperature are normal.
In hard-water conditions, mineral buildup can prevent the valve from seating fully after it has discharged. Sometimes a valve that opened once during a pressure event never fully re-seals afterward.
A worn valve needs to be replaced with a correctly rated unit – not just any valve, but one matched to your heater’s pressure and temperature specifications. Because this is a critical safety component, replacement should be done by a licensed technician who can also verify that the underlying pressure and temperature are within safe limits, so you are not just masking a bigger problem.
Critical Safety: Never Cap the Valve
This is the most important safety point on this topic: never plug, cap, or block a leaking relief valve to stop the drip. This valve is the last line of defense against a tank building up dangerous pressure. Disabling it can turn a leaking water heater into a serious hazard.
If your relief valve is leaking, treat it as a signal to investigate, not silence. Place a bucket under the discharge pipe to catch water, and make sure the discharge pipe is properly routed toward the floor and not obstructed.
Then call a licensed technician. A HeatLand technician can measure your system pressure, check the expansion tank, verify the temperature setting, and either correct the pressure issue or replace a worn valve – whichever the situation calls for. Serving Metro Vancouver and the Fraser Valley since 1999, our licensed, TSBC-certified team handles this common but safety-critical repair correctly.
Quick Checklist
- Never cap, plug, or block the relief valve
- Confirm the discharge pipe is unobstructed and routed to the floor
- Note whether the valve drips constantly or only during heating cycles
- Check if your home has a working expansion tank
- Verify the temperature setting is not excessively high
- Call a licensed technician to diagnose pressure or replace the valve
| Symptom | Likely Cause | Correct Fix |
|---|---|---|
| Drips during heating cycles | Thermal expansion / failed expansion tank | Install/repair expansion tank |
| Constant slow drip | Worn or debris-fouled valve | Replace the valve |
| Frequent discharge | High incoming pressure | Add pressure-reducing valve |
| Discharges plus very hot water | Temperature set too high | Lower and verify setting |
Frequently Asked Questions
Is it safe to use my water heater if the relief valve is leaking?
You can generally still use it short-term, but you should not ignore it. The leak signals either excess pressure or a worn valve, both of which need attention. Catch the drip in a bucket, keep the discharge pipe clear, and never cap the valve. Arrange for a licensed technician to diagnose it promptly.
Can I just replace the relief valve myself?
Because it is a critical safety component, and because a leak often points to an underlying pressure problem rather than the valve, this is best left to a licensed technician. Simply swapping the valve may not stop the leak if thermal expansion or a failed expansion tank is the real cause. Proper diagnosis matters.
What is an expansion tank and how does it relate?
An expansion tank absorbs the extra volume created when water heats and expands in a closed plumbing system. Without one, or with a failed one, that pressure has nowhere to go and forces the relief valve to weep on every heating cycle. Installing or repairing the expansion tank often resolves the leak.
Why should I never cap the relief valve?
The T&P relief valve is the last safeguard against dangerous pressure buildup inside the tank. Blocking it removes that protection and can lead to a serious failure. If the valve is leaking, address the cause – do not silence the symptom. Always keep the valve and its discharge pipe fully functional.
Reviewed by the HeatLand Heating & Cooling team — licensed HVAC contractor serving Metro Vancouver & the Fraser Valley since 1999. This article is for general guidance only. If you smell gas, suspect a carbon monoxide leak, or are unsure about any electrical or gas component, stop troubleshooting immediately and call a licensed technician or 911.