- Licensed plumbers, 24 hours a day, 7 days a week
- One price for the job, approved by you first
Call 1800 571 216: 24/7 · Book online
300+ five-star reviews · VBA accredited · Price approved before work starts
Why call OnCall
- VBA accredited, licensed and insured plumbers
- 300+ five-star reviews on Google
- More than 15 years on Melbourne callouts
- 24/7, including weekends and public holidays
- We find the cause, not just swap the valve
- Police checked and first aid verified
What our customers say
"After countless refusals from other plumbers I managed to get hold of Aiden and he DID NOT DISAPPOINT … In the end he completely solved the issue and even cleaned afterwards."
Tim Dacey, café owner, Google review
A Google review of OnCall's plumbing service.
Call 1800 571 216: 24/7 · 300+ five-star reviews
What the relief valve actually does
Most storage hot water units have a pressure and temperature relief valve, usually called a PTR valve, near the top of the tank. If the pressure or temperature inside the tank climbs too high, the valve opens and lets water out through the overflow pipe. It's there to stop the tank from being damaged.
Many systems also have an expansion control valve on the cold water side. As water heats, it expands, and this valve releases a small amount so the PTR valve doesn't have to do all the work.
Neither valve should ever be blocked, capped or tampered with.
Normal discharge vs a constant leak
This is the question most people ask, and here's the straight answer.
Usually normal: a small amount of water from the overflow pipe while the tank is heating, then it stops. That's expansion being released.
Not normal:
- a drip that never stops, day or night
- a steady stream or gush of water
- very hot water or steam coming from the pipe
- water from the valve body itself, not the overflow pipe
A constant leak means the valve has worn out, or something is pushing it open: high mains pressure, a failed pressure limiting valve, or a thermostat letting the tank overheat. That last one is why we always look for the cause, not just the symptom.
Pressure relief valve leaking? Do this
- Don't block or cap the overflow pipe.
- If it's discharging hot water or steam, switch off the power or gas to the unit and call us straight away.
- If it's pouring water, turn off the cold water valve on the unit or the water at the meter.
- Then call 1800 571 216.
Hot water system dripping overflow pipe: the common causes
- Worn PTR valve: the seat and spring wear with age and scale
- Worn expansion control valve on the cold side
- High mains water pressure, often with a failed or missing pressure limiting valve
- Thermostat fault letting the tank get too hot
- Sediment or debris stuck in the valve seat
If the valve is simply worn, replacement fixes it. If something else is forcing it open, a new valve alone won't last, so we fix the cause too and price it before doing anything.
How we fix it: assess, explain, approve, fix
Assess. We check the PTR and expansion valves, test the incoming water pressure, and check the thermostat and tank temperature.
Explain. You hear what's causing the discharge and whether it's the valve, the pressure, or the unit.
Approve. One price for the job, with your options laid out.
Fix. We replace the faulty valve (PTR valve replacement or expansion control valve replacement, or both), address the underlying cause if needed, then test the system and the safety valves before leaving.
What's included
- diagnosis of why the valve is discharging
- isolating and draining the system as needed
- removal of the old valve and supply and fitting of a suitable replacement
- checking the overflow pipe and fittings
- testing the new valve and the hot water system
Relief valves wear out with age. Your owner's manual will usually suggest how often to check and replace them, and it's part of every hot water system service we do. If a tempering valve is also leaking, we'll let you know.
Pricing
We charge by the job, not by the hour. A straightforward PTR valve replacement and a job that also needs a pressure limiting valve or thermostat are different jobs, so we confirm the cause on site and give you a clear price first. See hot water repair cost.
Relief valve FAQs
Is it normal for my hot water overflow pipe to drip?
A little water while the tank is heating is normal. A constant drip or steady flow isn't, and means the valve or the pressure needs checking.
What is a PTR valve?
It's the pressure and temperature relief valve on a storage hot water tank. It opens to release water if pressure or temperature gets too high.
Can I just block the overflow pipe?
No. Never block or cap a relief valve or its overflow. It's a key safety device.
Why does my new relief valve keep leaking?
Usually high mains pressure or a thermostat fault is forcing it open. We check those as part of the job.
Is a leaking relief valve an emergency?
If it's discharging hot water or steam, or pouring water, yes. Switch off the power or gas and call us. A slow drip can usually be booked in.
Can a relief valve be repaired?
Worn relief valves are replaced, not repaired. It's a quick job when the rest of the system is healthy.
Will a dripping relief valve damage my tank?
The drip itself won't, but the cause might. High pressure or overheating puts strain on the tank, which is why we check.
Overflow pipe won't stop dripping? Let's sort it.
A licensed OnCall plumber can find out why, price the fix and get it done once you say yes.
Call 1800 571 216: 24/7 · Book online
300+ five-star reviews · VBA accredited · Price approved before work starts
What happens next: we'll confirm your details, give you pre-arrival advice if you need it, and send a plumber. You'll get ETA updates on the way.