Should you repair or replace your radiator?
Updated August 2026
← Every repair-or-replace call
Repair a radiator that only runs cold or noisy, since a bleed, a $10–30 air vent, or a $75–200 supply valve fixes most of them; replace the cast-iron body only when it cracks or leaks, at $300–1,000 installed. A radiator that is cold at the top on a hot-water system almost always just needs bleeding, and a steam radiator that bangs or will not heat usually wants a new air vent or a properly pitched supply valve. Those are cheap, common fixes. The cast-iron section itself rarely fails, so a genuine replacement is reserved for a body that is cracked, rusted through, or weeping from a seam.
The short version
Radiators do not really follow the 50% rule, because the heating unit itself is nearly indestructible: cast iron routinely serves 50 years or more. Work the cheap causes in order first. Bleed a hot-water radiator to clear trapped air, replace a hissing or clogged air vent on a steam radiator for $10–30, and check that the supply valve opens fully and the radiator pitches slightly back toward the pipe. If it still will not heat after the vent and valve are sorted, the problem is usually a system-wide issue, sludge, a bad zone valve, or a circulator, not the radiator. The only clear replace is a radiator whose body leaks water onto the floor or has a cracked section, and even then a rebuilder can sometimes save an antique for less than the $300–1,000 swap.
Your situation, decided
| Situation | Verdict | Why |
|---|---|---|
| Hot-water radiator cold at the top, warm at the bottom | Repair | Trapped air; a two-minute bleed restores full heat |
| Steam radiator hissing or not heating | Repair | A $10–30 air vent is the usual culprit |
| Radiator not heating after bleeding | Repair | Check the $75–200 supply valve and its pitch next |
| Slow drip from a valve or union fitting | Repair | Repack or replace the valve; the radiator body is fine |
| Water weeping from a cracked cast-iron section | Replace | The pressure vessel has failed and cannot be patched |
| Radiator rusted through or freeze-cracked | Replace | Structural failure; swap the unit at $300–1,000 installed |
What each path costs
Repairs typically run $10–200; a replacement is $300–1,000 installed. A cast-iron radiator commonly lasts 50 years or more, so age almost never forces the call. Replace only a cracked, rusted-through, or freeze-split body; everything else is a repair. 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
Why is my radiator cold at the top but warm at the bottom?
That is the textbook sign of trapped air in a hot-water radiator, and it is a five-minute fix, not a repair bill. Air rises to the top of the radiator and blocks hot water from filling it. Open the bleed valve at the top with a radiator key or flat screwdriver, let the hissing air escape, and close it the moment water dribbles out. If several radiators need it, your system may be drawing in air and want a look at the pressure and the auto-vent. Make bleeding the radiators a start-of-season habit.
Can you repair a leaking cast-iron radiator?
It depends on where it leaks. A drip from a valve, union, or bleed fitting is a repair: repack or swap the part for $20–200. A leak from the cast-iron body itself, a hairline crack or a rusted seam between sections, is much harder. Epoxy and specialty sealants sometimes hold a minor weep temporarily, but a cracked section under system pressure is living on borrowed time. For a plain radiator, replacement at $300–1,000 is the honest fix; for an ornate antique, a radiator rebuilder can re-gasket and re-nipple the sections for a comparable sum.
Why does my steam radiator bang and knock?
Banging, or water hammer, means condensate is trapped where steam wants to travel, and it is almost always a pitch or vent problem, not a broken radiator. A steam radiator must tilt slightly back toward its supply valve so water drains out; one sitting flat or tilted the wrong way pools water and hammers. Shim the far legs to restore the pitch, and replace a clogged air vent for $10–30. Also open the supply valve fully, since a steam valve is meant to be all the way open or all the way shut, never throttled. Fix these before blaming the radiator itself.