Short answer
A dripping boiler is naming the broken part by where the water starts. A small valve with a metal lever is the pressure relief valve, and that is a repair. A wet pipe joint is a repair too, but water running out from under the casing on a boiler over 15 years old points at replacement. Put a dry pan under the drip today and book a heating tech, because a boiler holds hot water under pressure.
Find where the water starts in five minutes
- Wipe every wet surface dry with a rag and lay a sheet of cardboard under the boiler.
- Run the heat for two hours, then look for the first new wet spot on the cardboard and the pipes.
- Check the small valve with a metal lever on top of or beside the boiler. That is the pressure relief valve.
- Read the pressure gauge. A cold system sits near 12 to 15 psi. Over 30 psi opens the relief valve.
- Follow the discharge pipe down from that valve. Water inside the pipe means the valve opened, not that it failed.
- Feel the threaded joints on the pipes above the boiler for damp metal, rust streaks or white crust.
- Shine a light under the casing. Rust scale or water on the burner means the leak is inside the boiler.
If the water starts at the relief valve or a joint, this is a repair and the boiler stays. If water runs out from under the casing or drips onto the burner, the heat exchanger is leaking and the boiler needs replacing. Hire for this either way. A boiler carries gas, mains electricity and water near boiling, so the diagnosis ends where the casing opens.
Repair or replace
| Situation | What to do |
|---|---|
| Relief valve weeping, gauge over 30 psi | Repair. The expansion tank or the fill valve is driving pressure up and the valve is doing its job. |
| Relief valve weeping, pressure normal | Repair. Replace the valve. Old valves scale up and stop reseating. |
| Drip at a threaded joint or a pump flange | Repair. A new gasket or fitting fixes it and the boiler itself is untouched. |
| Water under the casing, boiler over 15 years old | Replace. A leaking heat exchanger is not repairable and the shell rusts from the inside. |
| Drip plus weak heat or weak hot water | Repair, then reassess. A leak bleeds system pressure, and one visit finds both faults. |
What it costs
Runhome contractor estimates for a dripping boiler ran from $305 to $695 to replace the safety valve and seals, and from $4,800 to $11,300 to replace the whole boiler, as of October 2026, including the trip and assessment.
| Option | Range |
|---|---|
| Repair, safety valve, fittings and system treatment | $305 to $695 |
| Full replacement, floor-standing boiler plus labour | $4,800 to $11,300 |
Can I do it myself?
No, not this one. You can dry the boiler, lay cardboard, read the pressure gauge and photograph the drip, and that shortens the visit and the bill. Everything past that means working on a sealed gas appliance holding water near boiling. Never cap, plug or tighten a relief valve to stop a drip, because that valve is the only thing keeping pressure from climbing. Hire a heating tech for the valve, the joints and anything under the casing.
What a contractor will ask you
Have these ready and you skip the back-and-forth.
- When the drip started, and whether that is days, weeks or months ago.
- How fast it drips: a steady drip, an occasional drip, or a small stream.
- Where the water starts: a pipe connection, a valve with a small lever, or under the casing.
- Whether that valve's pipe runs outside or stays inside the system.
- Floor-standing or wall-hung. A box on the wall is a combi, a unit on the floor is not.
- The age of the boiler, plus brand and model off the label if you can read it.
- Whether the drip follows a run cycle or shows up at random times.
- Whether heat and hot water are still normal, or lukewarm, short or showing error lights.
- A wide photo of the whole boiler and the wet area, not a close-up.
Common questions
- Why is water dripping from the valve with the little lever?
That is the pressure relief valve, and it opens when system pressure passes about 30 psi. Usually the expansion tank has failed, so pressure spikes every time the boiler fires. A valve that has opened a few times also stops sealing and needs replacing.
- Can I keep using the boiler while it drips?
Yes for a few days if the drip is slow and the heat still works. Put a pan under it and check it daily. Shut the boiler off and close its water feed if the drip turns into a stream or the floor stays wet.
- My boiler drips and the heat is weak too.
Those are usually one problem. A leak bleeds system pressure, and low pressure stops radiators filling and circulating. The tech should find the leak before topping the system up.
- Is a dripping boiler dangerous?
The water is not the danger, but what it reaches is. Drips rust the burner, the gas valve and the electrical controls under the casing. Once water has reached those, the boiler is a licensed tech's job.
- Should I repair or replace a 15 year old boiler that leaks?
Repair it when the leak is at a valve or a joint. Replace it when the water comes from inside the boiler body. A new safety valve on an old boiler is still worth the money while the shell is dry.