Hot water relief valve leaking: normal, or a fault?

Water under a hot water system is not always a failing tank. The relief valve is meant to release a little water as the tank heats. The question is how much, and whether it is going where it should.

Read from primary sources · Editor-reviewed · Current as at 20 September 2026

By the waterdamagequotesau.com editorial team · Published 20 September 2026 · Last reviewed 20 September 2026 · 7 min read

8 primary sources cited on this page. How we check what is on this site

Water under a hot water system is not always a failing tank. The relief valve is designed to let a little water out as the tank heats, and that water is supposed to go down a drain line. The question is how much, from where, and whether it is going where it should. The answer decides whether this is a valve for a plumber, a tank at the end of its life, or water damage already in the building.

Where the water is coming from, and what it means

Hot water system leaks by source, and what the published guidance says.
What you see	Likely meaning	What to do
A small discharge from the relief valve drain while heating	The valve relieving pressure, as designed	Watch it; the bucket test below
The drain line fills a bucket in a day	YourHome: a valve whose discharge fills a bucket in a day needs replacement	A licensed plumber
Water from the valve body, not the drain line	A valve or fitting fault	A licensed plumber
Water from the base or the tank jacket	Possibly the tank itself	Isolate the cold supply; a plumber; check the warranty
Discharge onto a floor, slab or into a cupboard	The drain line is missing, blocked or ends in the wrong place	A plumber; dry what it wet
Damp wall base or floor near an indoor unit	Water already in the building	Moisture readings; the hot water leak guide

The bucket test

Australian Government, YourHome: Hot water systems · Wayback Machine copy of 15 November 2025 (live page timed out), read 3 October 2026

The relief valve protects storage water heaters by relieving excess pressure. YourHome advises repairing a leaking relief valve immediately, and says tank warranties typically range from 5 to 10 years.

Put a bucket under the end of the relief valve drain line and leave it for a day. If it fills, the Australian Government’s advice is that the valve needs replacement. Rheem puts it a similar way for its own units: about 1/50 of the hot water used may discharge during each heating period, and more than a bucket in 24 hours may mean another problem. Note the date and the result; it is useful to the plumber and, if water damage follows, to the insurer.

Where the discharge must go

Government of Western Australia, Building and Energy, Technical Note: Water heater installations (version 6), citing AS/NZS 3500.4:2025 cl 5.11.3 · version 6, May 2026, read 3 October 2026

Where a relief valve drain line must discharge. The note says the line must have no tap or valve in it, fall continuously, and not discharge into a safe tray.

That is why a relief valve that drips onto a laundry floor or into a cupboard is a plumbing defect even if the valve itself is fine: the standard the regulator cites requires the discharge to go somewhere readily noticeable and harmless. A drain line that ends behind a wall or under a floor turns normal operation into slow water damage.

Get the water around the unit dried

Four digits, and restoration companies advertising for your postcode call you back. The plumber fixes the unit; the drying is separate.

Maintenance, replacement, and who can do it

Rheem Australia, installation instructions, gas outdoor 347 models (document 122638) · manufacturer instructions, read 3 October 2026

A manufacturer’s instruction for its own units, not a regulation. Rheem says the valve lever should be operated every six months, that the valve may discharge about 1/50 of the hot water used during each heating period, and that more than a bucket in 24 hours may indicate another problem.

Read that as what it is: a manufacturer’s instruction for its own units, not a rule that applies to every hot water system in Australia. The manual for your unit is the document to follow, and YourHome adds that copper and glass-lined tanks typically have a sacrificial anode that needs replacing every few years.

Who can fix it.

Queensland Building and Construction Commission, Notifiable work for home owners · read 3 October 2026

Notifiable plumbing work, which a licensed plumber completes and lodges with the QBCC within 10 business days. NSW Fair Trading says a licence or certificate is needed for any plumbing work in New South Wales, including hot water, regardless of cost.

Operating the relief valve lever as the manual describes is owner maintenance. Replacing a valve, a fitting or the unit is plumbing work: in New South Wales a licence or certificate is needed for any plumbing work including hot water, regardless of the cost, and in Queensland replacing a hot water heater is notifiable work. Gas and hard-wired electric units also need the gas or electrical side isolated by someone licensed for it.

If the water has already done damage

A leaking relief valve or tank becomes a water damage job when the water has gone into a floor, a wall base or a subfloor. That is the escape of liquid from fixed apparatus under reg 19(1)(a)(vi) (Insurance Contracts Regulations 2017 (Cth) reg 19(1)(a)(vi)); the valve or tank itself is where the wear and tear exclusion applies (Insurance Contracts Regulations 2017 (Cth) reg 19(2)(b)). Keep the failed part and the plumber’s written cause. On the published rate card, a laundry and the room next to it dried over the three-day minimum is $1,557 excluding GST. The hot water leak guide covers a full tank failure and the claim.

Common questions

Is it normal for a hot water relief valve to drip?

Some discharge is normal: the valve relieves pressure as the water heats. The Australian Government's YourHome guidance gives a simple test: if a bucket placed under the valve fills in a day, it needs replacement. Rheem's instructions for its units say discharge of more than a bucket in 24 hours may indicate another problem.

Why is my hot water system leaking from the bottom?

Water at the base can come from the relief valve drain, a fitting or the tank itself. A leak from the tank body is a different matter from a dripping valve: storage tanks do not get repaired from the inside, and YourHome says tank warranties typically run 5 to 10 years. A plumber decides which it is.

How often should a hot water relief valve be replaced?

Rheem's installation instructions for its units say at intervals not exceeding five years, more often where water deposits are high, and that the lever should be operated every six months. That is a manufacturer instruction for its own products; check the manual for your unit.

Where should the relief valve drain line go?

WA Building and Energy, citing AS/NZS 3500.4, says the drain line must have no tap or valve in it, fall continuously, not discharge into a safe tray, and end where discharge is readily noticeable and risks no damage to the building or injury.

Can I replace a hot water system myself?

No. In New South Wales a licence or certificate is needed for any plumbing work including hot water, and in Queensland replacing a hot water heater is notifiable work a licensed plumber lodges with the QBCC.

Is water damage from a hot water system covered by insurance?

The escape of water from fixed apparatus holding liquid is a listed event under reg 19(1)(a)(vi); the failed unit or valve itself is usually where reg 19(2)(b), wear and tear, rust and corrosion, applies.

Sources cited on this page

Every figure above was read from the source it is attributed to on 20 September 2026. How we check this.