A radiator that stays cold at the top while warm at the bottom is a classic sign of internal sludge, not just trapped air.
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Quick answer
A radiator is the heat-emitting unit in a hydronic heating loop, either older cast iron or newer steel panel style, and it needs replacing when it corrodes through, develops leaks at seams or valve connections that can't be reliably sealed, or when internal sludge buildup has reduced its heating capacity beyond what a flush can restore. In a Coquitlam home this often shows up as a radiator that stays cold at the top while warm at the bottom, or visible rust staining at a joint.
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In a hydronic heating system, radiators are where the actual room heating happens - hot water from the boiler circulates through the radiator body, and heat radiates and convects off its surface into the room. Cast iron radiators, common in older homes, hold a lot of thermal mass and heat a room slowly and steadily; steel panel radiators, more common in newer or renovated installations, are lighter and respond faster but hold less residual heat.
Either type relies on internal water flow staying unobstructed and the metal itself staying sound, and both of those things degrade gradually over decades of service rather than failing suddenly.
A tech distinguishes trapped air, which bleeding resolves quickly, from internal sludge buildup, which bleeding does not fix and which typically shows the same cold-top, warm-bottom pattern. Sludge (often magnetite, a black iron oxide that accumulates in older hydronic systems) settles at the bottom of a radiator and blocks circulation through the upper section over time.
They also inspect for pinhole leaks and corrosion at seams, especially on older cast iron units where decades of expansion and contraction cycles gradually work joints loose, and check whether the radiator's own shutoff and bleed valves are still functional.
A radiator suffering only from sludge buildup can often be flushed clean and returned to full capacity without replacement, which is always the first thing to attempt on an otherwise sound unit. Once a radiator has corroded through or developed leaks at multiple points, replacement is the more reliable path, and it's also an opportunity to consider whether a like-for-like cast iron replacement or a modern panel radiator better suits the room's heating needs and the system's overall condition.
Original cast iron radiator systems are most concentrated in Coquitlam's older housing stock - particularly in Maillardville, which has some of the area's earliest twentieth-century residential construction tied to its Francophone mill-town history, and in parts of Central Coquitlam - where decades of operation mean sludge accumulation is a genuinely common finding during service calls.
Coquitlam's comparatively soft, reservoir-sourced water limits scale-related radiator problems relative to hard-water regions, but it doesn't prevent magnetite sludge, which forms from internal corrosion over time regardless of water hardness. Newer construction near Burquitlam and the Evergreen Line corridor more often uses panel radiators or radiant floor heating instead of cast iron, so radiator replacement service calls there tend to involve newer-style units with different failure patterns.
Safety note
If you smell gas, hear an unusual burner sound, or a carbon monoxide alarm sounds, leave the home immediately and call FortisBC at 1-800-663-9911 from a safe location before doing anything else. Do not attempt to relight a pilot, reset a control, or inspect gas piping yourself. Only a Technical Safety BC licensed gas fitter should open, adjust, or replace gas-carrying or combustion-safety components.
This is a classic sign of internal sludge buildup rather than trapped air, since bleeding the radiator won't resolve a sludge blockage - a technician can confirm and recommend a system flush.
A single small leak at a fitting can sometimes be resealed, but corrosion through the radiator body itself or leaks at multiple points generally means replacement is the more reliable fix.
It depends on your system's overall condition and the room's heating needs - cast iron holds heat longer and steadily, while panel radiators respond faster, and a technician can help weigh the trade-off for your home.
It forms gradually from internal corrosion of iron and steel components over years of operation, which is why older systems, especially those with original cast iron radiators, are more prone to it.
Periodic flushing helps remove sludge before it significantly restricts flow, and it's a reasonable maintenance step for older hydronic systems, particularly those with cast iron radiators.
It depends on whether the system needs to be drained and how accessible the radiator is, but a technician can give you a time estimate once they've assessed your specific setup.
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