A boiler that keeps losing pressure usually has a small leak somewhere in the system or a relief valve that's releasing more than it should.
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A gas boiler that keeps losing pressure almost always has a leak somewhere in the closed loop, sometimes a visible drip at a fitting or valve, sometimes a slow pinhole leak in piping that's harder to spot, or a relief valve that's releasing small amounts of water due to a waterlogged expansion tank or excess pressure. A boiler that needs repeated manual top-ups, rather than holding steady pressure over weeks, needs a technician to find where the water is actually going.
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A hydronic boiler loop is a closed, sealed system, meaning the same water circulates through the boiler and piping repeatedly rather than being continuously replenished. In a properly sealed system, pressure should stay fairly steady over weeks and months, with only small seasonal fluctuations. Any meaningful, ongoing pressure drop means water is leaving the system somewhere, whether visibly through a drip or invisibly through a very slow leak or evaporation at a fitting.
The distinction matters because a one-time drop after a repair or a fresh fill is normal as air works its way out and the system settles, while a pattern of needing to top up pressure every few weeks or months is not normal and points to an active leak somewhere.
Visible leaks at pipe fittings, valves, or the circulator pump's seal are the easiest to find and often the easiest to fix. Less obvious are small pinhole leaks in older piping, more common in the historic downtown core and on older acreage farmhouses where original piping has had decades to corrode from the inside, sometimes accelerated by harder well water in rural parts of the city. A relief valve that's weeping, whether from a waterlogged expansion tank or a valve that's simply worn out, is another frequent cause that can look like a mysterious pressure drop if the discharge isn't obviously visible.
Newer subdivision homes in areas like Eagle Mountain generally have newer piping and fewer corrosion-related leaks, so a pressure drop in a newer home more often traces back to a specific fitting or the relief valve rather than generalized pipe corrosion.
Look along visible piping in the mechanical room or wherever pipes run through the basement or crawlspace for damp spots, mineral staining, or small drips, particularly at threaded fittings and valve connections. Check the area directly beneath the boiler and around the relief valve's discharge pipe for any wetness. Note how often you've had to add pressure and over what timeframe; that pattern is genuinely useful information for a technician trying to gauge leak severity.
Don't keep topping up pressure indefinitely without addressing the underlying leak; repeatedly adding fresh water introduces new dissolved oxygen into the system, which can accelerate internal corrosion over time.
| Situation | Typical Path |
|---|---|
| Single leaking fitting or valve | Repair, usually straightforward |
| Relief valve weeping due to waterlogged expansion tank | Expansion tank replacement |
| Multiple small leaks from aging, corroded piping | Broader piping assessment, may need partial repiping |
| Chronic pressure loss on an old boiler with corroded internals | Replacement conversation worth having |
Most pressure-loss calls resolve with a targeted repair. If the pattern points to a boiler and piping system that's genuinely at the end of its service life, replacement runs roughly $7,500 to $15,000 or more as a ballpark, not a quote.
Safety note
If you smell gas, hear hissing near the boiler, or see soot and yellow staining around it, leave the house first and call FortisBC's emergency line at 1-800-663-9911 from outside. Do not try to relight a pilot or reset anything until the line has been checked. Any gas boiler work in BC must be done by a Technical Safety BC licensed gas fitter; CANRO holds gas licence LGA0043870 and boiler licence LBP0046450.
A very occasional, small top-up, especially after service work, can be normal. Needing to do it repeatedly over weeks or months is not normal and means there's an active leak somewhere.
A homeowner can usually top up pressure at the fill valve if comfortable doing so, but it shouldn't be a repeated routine; the underlying leak needs to be found and fixed rather than continually compensated for.
Some leaks are very slow, at a pinhole in piping or a barely-weeping fitting, and can be hard to spot visually. A technician may need to pressure-test sections of the system to narrow down the source.
Not necessarily dangerous on its own, but a boiler running below its proper pressure range can trigger safety lockouts or fail to heat effectively, and an unaddressed leak can worsen over time.
It's a contributing factor in some cases, particularly in older piping on Abbotsford acreage properties, since harder water can accelerate internal corrosion over many years.
It's not usually an emergency, but it shouldn't be ignored indefinitely either, since repeated top-ups introduce fresh oxygen that can accelerate internal corrosion, and the leak itself may be worsening.
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