If you have a hot water tank, lift the lever on its relief valve gently every six months, let water run for a few seconds, then lower it gently again. Manufacturers also recommend having the valve checked or replaced at least every five years. It’s a 30-second job that keeps the most important safety device on your hot water system working.
Most people have never touched theirs. Here’s what the valve does, how to test it safely, what a leaking valve is telling you, and when to call us for hot water repairs.
What does a hot water relief valve do?
Water expands as it heats. In a sealed hot water tank, that extra volume has nowhere to go, so the pressure inside the tank rises. The relief valve is the safety outlet. When the pressure or temperature in the tank climbs too high, it opens and lets a little water out through a drain pipe.
The valve sits near the top of the tank, with a small lever on top and a copper drain pipe running from its side. Its full name is the temperature and pressure relief valve, but you may hear it called an expansion valve, a PRV, a PTR valve, a relief valve, or a TPR valve. Whatever the name, it’s the valve with the lever on your tank, and it’s the one this guide is about.
It matters because the alternative is dangerous. If the valve seizes and the thermostat fails, nothing stops the pressure building inside the tank. That’s why every mains pressure storage system must have one.
Which hot water systems have a relief valve?
Every storage tank system has one, including:
- electric storage tanks
- gas storage tanks
- heat pump systems
- solar systems with a storage tank
Continuous flow systems, such as instant gas units, don’t store hot water, so they don’t have a tank relief valve to test. If you’re not sure what you have, look for a tall cylinder with a lever valve near the top. If there’s no tank, this check doesn’t apply to you.
How to test your relief valve
Rheem’s owner’s guide says to operate the easing lever on the relief valve once every six months, and to raise and lower the lever gently. Here’s how:
- Find the valve near the top of the tank, and the drain pipe that runs from it.
- Check where the drain pipe ends, and keep everyone well clear. The water that comes out is hot enough to scald.
- Lift the lever gently until water flows from the drain pipe.
- Let it run for a few seconds to flush out any scale.
- Lower the lever gently. Don’t let it snap shut.
- Check that the flow stops within a minute or so.
Set a phone reminder for six months’ time. Pairing it with your flexi hose and water main checks makes it easy to remember.
What the test tells you
- Good flow that stops when you lower the lever: the valve is working.
- No water, or only a trickle: the valve may be seized or blocked with scale. Call a plumber.
- Water keeps running after you lower the lever: the valve may not be seating properly. Lift and lower it gently once more. If it still won’t stop, call a plumber.
Never force a stiff lever, and never block, cap, or plug the drain pipe to stop it dripping. That stops the valve doing its job.
Is a dripping relief valve normal?
A small drip while the tank is heating is normal. It’s the extra volume from expanding water being released, exactly as designed. You’ll usually notice it most after a lot of hot water has been used and the tank is reheating.
What isn’t normal:
- constant dripping, day and night, even when the tank isn’t heating
- steam or very hot water coming from the drain pipe
- water leaking from the tank itself, rather than the drain pipe
- water pouring out in a steady stream
Why a relief valve leaks constantly
The most common causes are:
- a failed pressure limiting valve: if the valve that controls the incoming water pressure stops working, the pressure in the tank stays too high.
- a worn valve: age or scale stops the valve sealing.
- high mains pressure: Rheem says an approved pressure limiting valve is needed where mains pressure is too high for the system. Without one, the valve keeps relieving.
- overheating: a faulty thermostat can let the water get too hot, so the valve opens to release it.
Mains pressure varies a lot across Sydney. Sydney Water says its network averages 52 metres head, but some customers receive more than 100, mostly in low-lying parts of each supply zone. If your relief valve drips constantly, a quick pressure test is a good place to start.
A leak from the tank itself, rather than the drain pipe, usually means the tank is failing. If that’s the case, turn off the water supply to the tank, or turn off your water main, and call us. For an electric tank, switch it off at the switchboard too.
When should the relief valve be replaced?
Rheem says the relief valve should be checked for performance or replaced at intervals of no more than five years. In areas with a lot of mineral deposits in the water, that may need to be more often.
As a rule of thumb:
- any time it fails a test: a plumber replaces it straight away
- every five years: a plumber checks or replaces the valve
- every six months: you test the lever
Replacing a relief valve is a quick job for a licensed plumber. It needs the right valve for your system, because each one is rated to a set pressure. A wrong valve can either leak constantly or fail to open when it should. When we replace one, we also check the drain pipe, the incoming water pressure, and any other valves on the system, so the new valve isn’t fighting a problem somewhere else.
Some systems also have a valve on the cold water pipe going into the tank that takes some of the pressure load off the relief valve. The Queensland Government notes it may help extend the life of the relief valve and the tank. You don’t need to do anything with it yourself. We check it as part of any hot water service.
It’s also a good chance to look at the rest of the system. If your tank is old, running out of hot water sooner than it used to, or rusting at the base, a new valve may only delay the inevitable.
Hot water relief valves in rental and strata homes
In a rental, tell your agent or landlord about a constantly leaking relief valve. It wastes water and can point to a fault that gets worse. If the hot water stops working altogether, NSW treats it as an urgent repair, and tenants should tell the landlord or agent straight away. In apartments, hot water tanks often sit on balconies or tucked into cupboards, so check where the drain pipe ends and that it drains somewhere safe.
We look after hot water systems across homes and rentals in Dulwich Hill, Leichhardt, Marrickville, and beyond, and we’re happy to deal with agents and property managers directly.
Frequently asked questions
How often should I test my hot water relief valve?
Every six months. Lift the lever gently, let water run for a few seconds, and lower it gently again. Have a plumber check or replace the valve at least every five years.
Is it normal for my hot water relief valve to drip?
A small drip while the tank is heating is normal. Constant dripping when the tank isn’t heating, a steady stream of water, or steam is not, and it’s worth having checked.
Why won’t my relief valve stop leaking after I tested it?
Lift and lower the lever gently once more to help it reseat. If it keeps running, the valve may be worn or holding scale, or your water pressure may be too high. Call a plumber.
Does a continuous flow hot water system have a relief valve to test?
Not a tank relief valve. Continuous flow units heat water as it passes through and don’t store it, so there’s no tank to relieve. Check your owner’s manual for any servicing the unit needs.
Book a hot water relief valve check
Richard Knight Plumbing has been looking after Inner West hot water systems from our base on Raper Street, Newtown, since 2005. We can test and replace relief valves, fit a pressure limiting valve if your mains pressure is high, and tell you honestly whether your system has years left in it. It’s all part of our plumbing maintenance service.
We work Monday to Friday, 7 am to 5 pm, across all the suburbs on our service area page. Call 1300 300 941 or request a quote, and we’ll get back to you with clear advice and an obligation-free quote.