Boiler Leaking Water: Causes, Risks & What to Do
Water around your boiler is never normal. Here are the five most common causes of boiler leaks in BC homes and the steps to take right now.
A leaking boiler will not resolve on its own. What starts as a drip at a pipe joint can escalate to corrosion, pressure loss, and eventual system failure. More importantly, water near gas components creates safety risks that BC's Technical Safety Authority (TSBC) takes seriously. Here's what to check and how to respond.
5 Most Common Causes of Boiler Leaks in BC
1. Pressure Relief Valve (PRV) Discharge
The PRV is a safety device designed to open when system pressure exceeds its rated limit — typically 30 psi (2 bar) on residential boilers. A continuous drip from the PRV discharge pipe usually means either the system pressure is chronically high, or the valve itself has failed and is weeping at normal pressure. Never cap or plug the PRV discharge — this is illegal under BC safety codes and creates a serious explosion risk. A dripping PRV needs immediate assessment by a licensed gas-fitter.
2. Pump Seal Failure
The circulator pump moves heated water around your hydronic system. The pump shaft is sealed where it enters the pump body, and these seals can fail after years of service — typically 10–15 years on residential units. A failing pump seal produces a steady drip directly beneath the pump, often leaving a rust stain on the boiler cabinet. The pump can usually be replaced without draining the entire system.
3. Pipe Joints and Compression Fittings
The copper and CPVC piping connected to your boiler passes through numerous fittings, valves, and unions. Over time, especially after temperature cycling through many Vancouver winters, compression fittings can loosen and soldered joints can develop hairline cracks. These leaks are typically slow but constant, and the mineral-rich water in the Lower Mainland can leave distinctive white calcium deposits that make the source easy to trace.
4. Cracked or Corroded Heat Exchanger
The heat exchanger is the core of your boiler — it transfers heat from the burner to the water without the two mixing. A cracked or corroded heat exchanger is the most serious cause of a boiler leak. Signs include water appearing at the bottom of the boiler (not at any visible fitting), a drop in hot water temperature, or a wet burner area. A failed heat exchanger on most residential boilers is an economic write-off — replacement costs typically exceed the value of a boiler over 10 years old.
5. Expansion Tank Waterlogged or Failed
The expansion tank absorbs the pressure increase as water heats and expands. When the tank's internal bladder fails, it fills with water and loses its ability to buffer pressure swings — causing the PRV to open repeatedly. The tank itself may leak from its port or fitting. Expansion tanks on typical Metro Vancouver residential boilers last 8–12 years. Replacement is a straightforward repair that restores proper system pressure behaviour.
Safety Steps Before the Technician Arrives
While you wait for service, take these steps to contain the situation:
- Place a towel or container under the leak to protect flooring and prevent water from reaching electrical components.
- Note the pressure gauge reading. Take a photo on your phone — this helps the technician understand the system state at the time of the leak.
- Do not turn off the gas supply unless you smell gas or there is active water contact with electrical components.
- Photograph the leak source — even a blurry image of where the water is coming from speeds up diagnosis significantly.
When a Boiler Leak Is an Emergency
Call immediately — do not wait — if any of the following are present:
- You can smell gas alongside the water leak
- Water is dripping onto or pooling near gas lines, the burner assembly, or electrical wiring
- The leak rate is increasing rapidly — a slow drip that becomes a steady flow within an hour
- You notice water staining on the ceiling below an upper-floor boiler room
In an emergency, shut off the water supply to the boiler via the cold-water isolation valve (typically a quarter-turn ball valve on the incoming cold-water pipe to the boiler). This will slow or stop the leak. For gas concerns, call FortisBC at 1-800-663-9911 first. Our Red Seal gas-fitters serve Metro Vancouver and can typically respond the same day for active leaks.
Related Issues & Repairs
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