Should you repair or replace your boiler?
Updated August 2026
← Every repair-or-replace call
Keep repairing a boiler until it is past about 20 years or its efficiency drops below 80%; replace when the block cracks or the vessel itself leaks. Boilers are long-lived, 15–30 years depending on type, and most faults are peripheral: a circulator pump, expansion tank, aquastat, or ignition part runs $200–1,200 to fix against $5,000–10,000 for a new boiler installed. Those repairs stay worthwhile for most of the unit's life. The line to replacement is drawn by the pressure vessel, because a cracked cast-iron block or a leak from the boiler body cannot be repaired.
The short version
A boiler is one of the few systems where repair stays the right answer for decades. Cast-iron units in particular can run 30 years, so a $400 circulator pump or a $250 aquastat on a 15-year-old boiler is money well spent. Apply the 50% rule only once you are past 20 years or the boiler's efficiency has slipped under 80%, where a modern condensing unit at 90-plus percent starts paying you back on fuel. The vessel is the hard stop. If the cast-iron sections crack or the boiler leaks from the body rather than a fitting or valve, no repair restores it, and the age no longer matters.
Your situation, decided
| Situation | Verdict | Why |
|---|---|---|
| Circulator pump, expansion tank, or aquastat failed | Repair | A $200–1,200 peripheral part on a boiler with life left |
| Ignition or control fault, boiler under 20 years | Repair | A routine fix; the vessel is still sound |
| Cracked cast-iron block or leaking vessel | Replace | The pressure vessel cannot be repaired, at any age |
| Past 20 years, efficiency below 80% | Replace | A 90%+ condensing boiler pays back on fuel over time |
| Low pressure from a bad fill valve or a leak at a fitting | Repair | A $150–400 valve or joint fix, not a new boiler |
| Repeated repairs on a 25-year-old boiler | Replace | The 50% rule; you are past the reliable service window |
What each path costs
Repairs typically run $200–1,200; a replacement is $5,000–10,000 installed. Boilers last 15–30 years, cast iron longest. The 50% rule waits until year 20 or sub-80% efficiency; a cracked block ends it at any age. Price your own number on the home maintenance cost calculator before you commit either way.
The repair-or-replace call is easy when you know the unit's age and service history. OnOtto keeps both, plus the maintenance that delays this decision for years.
Start your home's service log, freeFrequently asked questions
How do I tell a cracked block from a fixable leak?
Trace where the water comes from. Drips at a circulator flange, a fitting, the pressure-relief valve, or the expansion tank are threaded or bolted parts, each a $150–400 repair. Water seeping from the cast-iron sections themselves, or pooling under the body with rust streaks down the block, points to a cracked vessel, which is terminal. A technician can pressure-test to confirm. Watch your boiler pressure: a gauge that keeps dropping and needs constant topping up often signals a leak worth chasing down before it worsens.
Is a 90% condensing boiler worth replacing an 82% unit?
Eventually, but rarely as an emergency. Jumping from roughly 80% to 90-plus percent efficiency trims fuel use, but a new boiler is $5,000–10,000, so the payback runs years and depends on your climate and fuel price. If your current boiler is under 20 years and only needs a $400 pump, repair it and plan the upgrade later. If it is past 20, inefficient, and facing a large repair, replacing is the moment the efficiency gain and the avoided repair finally line up. Do not scrap a sound mid-life boiler on efficiency alone.
Does annual service extend a boiler's life?
Considerably, and it protects the parts that strand you in winter. A yearly boiler service checks combustion, cleans the burner, verifies pressure and the expansion tank, and catches a weakening circulator before it quits. Water quality matters too, since correct pressure and an intact expansion tank keep the vessel from stress cycling. A serviced boiler routinely reaches the top of the 15–30 year range, while a neglected one loses efficiency and fails parts early. The service is a small fraction of a $5,000–10,000 replacement.