When your boiler quits or your water heater starts making noise, you’re facing the most common decision in home mechanical systems: fix it, or replace it? Here’s the framework we use on every call — the same one we show customers before they decide.
The 50% Rule
If a repair costs more than 50% of the replacement cost — and the equipment is past the midpoint of its expected life — replacement is almost always the smarter financial decision. You’d be paying premium money for borrowed time.
Two real scenarios
Scenario A — repair it. A 12-year-old gas boiler needs a circulator pump: $850 repair against a $5,500 replacement. That’s 15% of replacement cost on a boiler with 13+ years of life left. Cheap fix, easy call — replacing now would throw away years of value you’ve already paid for.
Scenario B — replace it. A 22-year-old gas boiler with a cracked heat exchanger: $3,200 repair against the same $5,500 replacement. That’s 58% of a new system, on equipment past its midpoint. The math says replace — and a new high-efficiency unit may qualify for Mass Save rebates that shrink the gap further.
Typical equipment lifespans
- Gas boiler: 25–35 years — start evaluating replacement around year 20
- Oil boiler: 20–30 years — an oil-to-gas or heat pump conversion often makes sense after year 15
- Gas furnace: 15–20 years — a cracked heat exchanger is a safety issue; always replace
- Tank water heater: 8–12 years — plan for replacement after year 10
- Tankless (Navien): 20+ years with annual service
- Central A/C: 12–17 years — R-22 systems should be replaced, that refrigerant is discontinued
- Ductless mini-split: 15–20 years
- Expansion tank: 5–10 years — inexpensive; replace proactively
Age isn’t the whole picture
Efficiency gains, available rebates, and how long you plan to stay in the home all factor in. A 20-year-old system running at 70% efficiency costs you money every month it stays — sometimes replacement pays for itself faster than you’d think.
Facing this decision right now? Call 3R Plumbing & Mechanical at (781) 974-5239. We’ll quote the repair and the replacement side by side — and give you an honest recommendation either way.