PVC Pipe Leaking at a Water Heater: Which Pipe?
On this page (5 sections)
The Short Answer: Several different white plastic pipes can connect to a water heater: a small condensate drain on condensing gas and heat-pump models, larger vent pipes on power-vent and condensing gas models, and sometimes the relief-valve discharge line. Each leaks for different reasons. A dripping condensate drain is usually a minor fix; a leaking vent joint is a carbon monoxide concern; and a relief-valve line in standard PVC may not be rated for the water it carries.
Identify the pipe
| Pipe | Where it goes | What a leak usually means | Urgency |
|---|---|---|---|
| Small (often 1/2 or 3/4 inch) tube from the bottom or side of a condensing gas unit or heat-pump heater | To a floor drain, pump, or neutralizer | Clogged trap or line, poor slope, a loose joint, or a failed condensate pump | Fix soon to prevent water damage |
| Larger (2 or 3 inch) pipes from the top of a power-vent or condensing gas unit | Outdoors through a wall or roof | Joint separated or poorly sloped vent, letting condensate (and possibly exhaust) escape | Prompt service; possible CO risk |
| Pipe from the relief valve on the side or top of the tank | Down toward the floor or a drain | Relief valve discharging, or the pipe itself cracking from hot water | See below |
| Any pipe connecting directly to the hot or cold water connections | The home’s water lines | Should not be standard PVC; under pressure and heat it can fail | Close the cold inlet and call a plumber |
Water from condensate drains and vents is usually cool and appears only while the heater runs. A. O. Smith’s condensation bulletin (opens in a new tab) explains how much condensation gas heaters produce and why it can be mistaken for a leak.
Condensate drains
Condensing gas water heaters and heat-pump heaters produce water as they run. It drains through a trap and a small line. Common failures are a trap clogged with debris, a line that sags or runs uphill, a loose slip joint, or a condensate pump that has stopped. On condensing gas units, condensate is mildly acidic, which is why some installations include a neutralizer. If your owner’s manual describes cleaning the external condensate trap or line as owner maintenance, follow it; otherwise, have it serviced. Navien condensate drain leaking covers one manufacturer’s setup in detail.
Vent pipes
On power-vent and condensing units, PVC, CPVC, or polypropylene vent pipe carries exhaust outdoors. The manufacturer specifies which materials and slope are allowed. A joint that drips condensate may also leak exhaust. Do not tape or seal it yourself; turn the heater off and have the vent inspected. Water heater vent pipe leaking explains how vent leaks are diagnosed.
Relief-valve discharge in PVC
The relief valve discharges water that can be at or near boiling. Plumbing codes generally require discharge piping rated for that temperature, such as copper or CPVC; ordinary PVC is rated for far lower temperatures and can soften, sag, or crack. If your relief valve drains through standard PVC and it is leaking, have a plumber replace the line, and find out why the valve is discharging; see why the relief valve keeps discharging. Never cap the line.
Frequently Asked Questions
Q: Is it normal for water to come out of the small white tube on my water heater? A: On condensing gas and heat-pump models, yes: that tube carries condensate to a drain while the unit runs. The problem is water escaping before it reaches the drain, or a pump that has stopped.
Q: Can I glue a leaking PVC joint myself? A: A condensate drain line is low-risk plumbing, but a vent pipe carries exhaust and must be repaired with the manufacturer’s specified materials and slope. For vents, call a technician.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- A. O. Smith technical bulletin 15: condensation (opens in a new tab)Why combustion condensate can resemble a tank leak; not a diagnosis of another manufacturer’s model.
- CPSC: carbon monoxide fact sheet (opens in a new tab)Carbon monoxide hazards and emergency response.
Editorial standards and corrections · Prepare a useful service request