What Pressure Loss Actually Means
A sealed heating system holds a fixed amount of water under pressure, normally showing about 1.0–1.5 bar on the gauge when cold. That pressure should stay stable for months. If yours keeps falling and you find yourself topping it up with the filling loop every week or two, that water is going somewhere — the system can't simply lose pressure without losing water.
There are only really two ways water leaves a sealed system: it escapes as a leak, or it's vented out by the pressure relief valve. Many homeowners assume "no visible puddle" means "no leak," but plenty of leaks are slow, hidden behind walls or under floors, or evaporate off hot pipes before they ever pool.
Continually refilling masks the problem and, worse, feeds fresh oxygenated water into the system, accelerating internal corrosion. The right move is to find the leak, not keep topping up.
Where Hidden Leaks Hide
Under floors and behind walls. In homes with hydronic or in-floor heating — common in Greater Vancouver — pipe runs travel under flooring and through wall cavities. A pinhole leak there can drop your pressure for weeks while the only sign is a faintly warm or damp patch of floor, or no visible sign at all.
The pressure relief valve. A relief valve that's weeping — because of high pressure from a waterlogged expansion vessel, or a worn valve seat — quietly discharges water out the external pipe. You lose pressure but see nothing indoors.
Internal boiler components. A heat exchanger that leaks internally, or seals that weep only when hot, can shed water that evaporates off warm surfaces inside the casing, leaving no puddle.
Radiator and towel-rail valves. Slow seepage at a valve gland or bleed point, often evaporating before it's noticed, adds up over time.
The Expansion Vessel Red Herring
Here's a subtlety worth understanding: a failed expansion vessel can cause pressure loss without any leak at all. When the vessel loses its air charge, pressure swings wildly — spiking when the system heats (often opening the relief valve, which then discharges real water) and dropping low when it cools.
So a system with a waterlogged expansion vessel can both lose water (via relief valve discharge) and appear to lose pressure dramatically as it cools. This is why a good diagnosis doesn't just hunt for puddles — it tests the expansion vessel's charge and watches how pressure behaves across a full heat-and-cool cycle.
Getting this right matters. Chasing a phantom pipe leak when the real issue is a $-modest expansion vessel wastes time and money. Equally, replacing the vessel when there's a genuine hidden pipe leak won't solve anything. Proper diagnosis distinguishes the two.
How We Find Hidden Leaks
Finding an invisible leak is detective work. We start by isolating the variables: testing whether the relief valve is discharging, checking the expansion vessel's air charge, and observing pressure behaviour across heating and cooling cycles. That alone resolves a large share of "mystery" pressure loss.
If the loss points to the pipework rather than the boiler or relief valve, we can pressure-test sections of the system and inspect accessible runs, valves, and connections. For genuinely concealed leaks under floors, we trace the most likely zones methodically rather than tearing up flooring at random.
Throughout, we keep you informed — what we've ruled out, what we suspect, and what each next step involves. The goal is to find the source with the least disruption, then fix it once, properly.
Stop Topping Up — Get It Diagnosed
If you're refilling your boiler more than two or three times a year, that's not normal and it's worth investigating before it corrodes the system or causes hidden water damage. The constant fresh-water top-ups are quietly shortening your boiler's life.
GasBoilers.ca, a CanroHeat Division, finds and fixes pressure-loss leaks across Vancouver, Burnaby, Richmond, Surrey, Coquitlam, the North Shore and the wider Lower Mainland. We diagnose the true cause — relief valve, expansion vessel, internal fault, or hidden pipework — and repair it. Call 604-359-1081 for an exact quote after diagnosis, with same-day and weekend service where possible.