A Tsawwassen boiler that keeps losing pressure almost always has a slow leak somewhere in the system, and finding it is more about patience than guesswork.
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A boiler that gradually loses pressure over days or weeks, needing repeated top-ups, almost always has a slow leak somewhere in the closed system — at a fitting, a valve, a radiator, or the relief valve weeping slightly. A pressure drop that happens quickly rather than gradually points to a more obvious leak or a fitting failure and deserves prompt attention rather than just another top-up.
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A properly sealed hydronic system is a closed loop — the water inside stays inside, and pressure should hold steady between services aside from small seasonal shifts as the water temperature changes. When pressure keeps dropping and needs regular top-ups, water is escaping somewhere, even if it isn't visible as an obvious puddle. Small, slow leaks often evaporate before they're seen, especially at a fitting inside a wall or under insulation.
The rate of loss is a useful clue: pressure that drifts down slowly over weeks suggests a small leak, while pressure that drops noticeably within a day or two suggests something larger, like a failed fitting or a relief valve that's discharging more than it's weeping.
Tsawwassen's older bungalows and ranchers, many still on original hydronic piping from the 1960s and 70s, are more prone to small leaks developing at aging fittings and valve packings over time than a newer system, simply from decades of thermal cycling on the same joints.
It's also worth checking whether pressure loss correlates with the system actively heating versus sitting idle, since a leak that only shows up while the boiler is running and pressure is at its highest points toward a fitting or seal that's marginal under normal operating pressure but not enough to leak when the system has cooled down and settled at its lower, resting pressure.
A technician pressurizes the system and inspects accessible fittings, valves, and radiators for visible weeping, checks the expansion tank's air charge since a waterlogged tank can present as pressure loss through a weeping relief valve, and traces piping where practical for hidden leaks. On older homes, this sometimes means checking sections of piping behind finished walls or under flooring where a past leak has left mineral staining.
Most pressure loss is fixed by repairing or replacing a single fitting, valve, or the expansion tank — a routine, targeted repair. A pinhole leak in an old radiator sometimes means replacing that radiator rather than trying to repair it, but this is isolated to that component and doesn't point toward boiler replacement.
Most residential hydronic boilers run a cold fill pressure somewhere around 12 to 15 psi, rising somewhat as the system heats, with the exact figures depending on the system's design and how much piping sits above the boiler in a multi-storey home. Knowing your system's typical cold reading makes it much easier to notice a slow decline early, rather than only realizing there's a problem once the boiler starts locking out on low pressure or a room stops heating properly.
A simple habit of glancing at the pressure gauge every few weeks during the heating season, particularly after any cold snap, is a low-effort way to catch a developing leak well before it becomes an emergency.
A leak small enough to only lose a few psi over a week or two often evaporates before it ever forms a visible puddle, especially at a fitting hidden inside a wall cavity, under floor insulation, or behind a finished basement ceiling from a past renovation. Mineral residue left behind after the water evaporates is sometimes the only visible clue, appearing as a faint white or rust-coloured stain near a joint rather than active dampness.
This is why a technician often relies on pressurizing the system and watching the rate of decline over time, combined with a careful visual inspection of every accessible fitting, rather than expecting to spot an obvious drip on the first visit.
If the system has an automatic fill valve that tops up pressure on its own, it can mask a slow leak for a long time by continuously making up the lost water, which is worth mentioning to a technician since it changes how a leak would present — as rising water bills or a fill valve that's constantly cycling rather than an obvious drop on the pressure gauge.
A technician can usually confirm which of these is happening with a straightforward pressure test during a single visit, rather than needing to observe the system over several separate appointments.
Safety note
This system is connected to a gas-fired boiler, so any repair involving its piping, valves, or controls should be done by a Technical Safety BC licensed gas fitter. If you ever smell gas near the boiler, leave the home immediately and call FortisBC at 1-800-663-9911 from outside.
Some very gradual seasonal drift is common, but needing to top up pressure regularly points to a slow leak somewhere in the system that's worth tracing.
Pressure that drops slowly over weeks suggests a small leak, while a noticeable drop within a day or two suggests something larger that should be looked at promptly.
Occasional small top-ups aren't harmful, but repeatedly doing so without finding the leak means the underlying problem keeps going untreated and could be masking something like a waterlogged expansion tank.
Homes still on original hydronic piping from the 1960s and 70s have had decades of thermal cycling on the same fittings and valve packings, which makes small leaks more likely to develop over time.
Yes, a relief valve that's weeping slightly, often due to a waterlogged expansion tank, can account for gradual pressure loss without an obvious puddle anywhere.
No, this is a water-side issue rather than a combustion or gas safety issue, though any persistent leak is worth having diagnosed and repaired.
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