Heating
How Do Radiators and Boilers Work in an Older Toronto Home?
Many older Toronto homes still heat with a central boiler and radiators instead of a furnace — here's how the system works, why one radiator can stay cold, and when a problem is plumbing versus a heating job.
A boiler and radiator system heats your home by warming water (or steam, in older setups) in a central boiler and pushing it through pipes to metal radiators, which release that heat into each room. It's common in older Toronto housing stock — century homes, older semis in neighbourhoods like Riverdale or the Annex, and pre-war apartment buildings often still run on it. The system is usually reliable for decades, but it depends on water moving freely through the pipes, which is where most homeowner problems start.
How does a boiler and radiator system heat a home?
The boiler heats water and a pump circulates it through a loop of pipes to each radiator, where the heat radiates into the room before the cooled water flows back to be reheated. Some older buildings use steam instead: the boiler makes steam that rises to the radiators and condenses back to water as it gives off heat — you can usually tell which type you have by whether your radiators have one pipe or two, and whether they hiss as steam moves through them. Either way it's a closed loop, so it should need topping up with water only occasionally, not constantly.
Why does one radiator stay cold while the others heat up fine?
The most common cause is trapped air, fixed by "bleeding" the radiator — opening the small valve at the top with a radiator key until water flows out steadily with no more hissing. If bleeding doesn't fix it, the culprit is often a stuck valve at the base or sediment settled inside, especially in a system that hasn't been serviced in years. A radiator that's cold at the bottom but warm at the top is usually pointing to sludge buildup rather than trapped air, and that's better left to someone who works on these systems regularly.
Why does my radiator make banging or gurgling noises?
Banging in a steam system is almost always trapped water — a radiator that isn't pitched slightly toward its inlet can trap water and cause the pipes to hammer as steam pushes past it. Gurgling in a hot-water system usually means air in the lines, same fix as the cold-radiator problem above. Noise that persists after bleeding often means the whole system needs air purged at the boiler itself, which isn't a homeowner-level fix.
Is a leaking boiler or radiator an emergency?
Water pooling under a radiator or boiler is worth shutting the system down for and getting looked at quickly, since a small leak can turn into a bigger one and pressure loss can eventually stop the system from heating properly. It's not usually the kind of "call right now" emergency that a burst supply pipe is, unless the leak is heavy or you smell gas near the boiler — that's a genuine emergency. For a slow drip that's clearly coming from a radiator valve, it's reasonable to shut the valve, mop up, and book a visit.
Is this a plumbing job or a heating job?
Radiators, the pipes feeding them, and valves are generally plumbing work, while the boiler's burner, gas connection, and combustion components lean toward heating and gas-fitting work that legally requires a licensed trade. A lot of technicians who service these systems handle both sides, but it's worth asking directly what someone is qualified to touch before they start, especially anything involving the gas line. If you're not sure which category your problem falls into, describing the symptom — cold radiator, noisy pipes, leak, no heat at all — is usually enough for whoever you call to sort it out.
Frequently asked questions
How often should I bleed my radiators? Once a year, typically at the start of the heating season, is enough for most homes — bleeding the same radiator repeatedly within a season usually points to a leak or a failing valve, not normal air buildup.
Can I just replace an old radiator myself? Swapping a radiator means draining part of the system and disconnecting old valves that are often corroded after decades, so most homeowners have someone experienced handle it even though the radiator itself is a simple part.
Do these systems need annual maintenance like a furnace does? Yes — a boiler benefits from a yearly check similar to furnace servicing, covering pressure, water quality in the loop, and the burner or gas components, and staying on top of it tends to catch small issues before a no-heat situation in January.
If your radiators are acting up before the heating season really kicks in, it's worth getting eyes on the system now rather than after the first cold snap — request a plumber or message us on Facebook. Free for homeowners, care of GetFixHero.
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