The short answer

15–25 yearstypical boiler (radiators/radiant) lifespan

The band covers hot-water and steam boilers feeding radiators, baseboard, or radiant floors. Construction matters more than brand: old cast-iron sectional boilers are slow, heavy, and famously long-lived, while modern high-efficiency condensing boilers trade some of that longevity for much lower gas bills, and their heat exchangers are sensitive to water quality and to running without a service. Combi boilers, which also make your hot water, work every time someone showers and tend to land at the shorter end. If you don’t know your boiler’s age, the rating plate inside the cover usually shows a manufacture date or a serial number that encodes one.

What shortens or extends its life

Shortens it

• Skipping the annual service, so a clogged burner, failing seal, or blocked condensate line goes unnoticed• Frequent top-ups with fresh water: every refill brings in oxygen and minerals that corrode and scale the heat exchanger• Sludge from corroding radiators circulating through the system• Short cycling from a boiler sized too big for the house• A frozen or blocked condensate pipe on a condensing boiler, which shuts it down and stresses it

Extends it

• A yearly service by a licensed heating technician: burner, seals, flue, and safety controls• A magnetic filter and inhibitor in the water to keep sludge out of the heat exchanger• Holding the pressure in the normal range instead of topping it up repeatedly• Fixing small leaks quickly, since a leak is what makes those fresh-water top-ups necessary

Warning signs it’s failing

• Pressure that keeps dropping and needs topping up every few weeks: a leak somewhere in the system• Kettling, banging, or gurgling while it heats, often scale or sludge on the heat exchanger• Radiators that stay cold at the bottom even after bleeding, a sign of sludge• A yellow or orange burner flame instead of a crisp blue one, which needs a technician right away• Rust, water, or soot around the boiler or the flue

What replacement costs

$4,000–$10,000 installedfor a like-for-like gas boiler replacement, varying with output, venting, and how much near-boiler piping has to change. High-efficiency condensing and combi units sit at the upper end; oil boilers and steam systems often run higher. Older radiators and piping can usually be kept. Get at least two quotes, and ask each installer to size the boiler from a heat-loss calculation, not from the old unit’s label.

Maintenance that extends its life

Book an annual boiler service

Before the heating season starts. The technician cleans the burner, checks seals and the flue, and tests the safety controls.

Check the pressure gauge every few months

Know what normal looks like on yours (often 12–15 psi cold on a hot-water system). A steady drop means a leak to find, not a habit of topping up.

Bleed the radiators once a year

Release trapped air at the start of the season so every radiator heats top to bottom. Check the pressure again afterwards.

Keep the condensate pipe clear

On a condensing boiler, make sure the outdoor drain pipe can’t freeze or clog. It’s the most common winter shutdown.