It's the vent, not the boiler
Steam can't enter a radiator full of air. The air vent's job is to let that air escape as steam rises — when the vent works, steam fills the radiator and it heats. When the vent fails (clogged, stuck closed, or hissing constantly), the air stays trapped and the radiator stays cold. The boiler is fine; the radiator just can't get the steam in.
How to tell which it is
A cold radiator with a silent vent usually has a stuck-closed vent. A radiator that hisses loudly and never gets fully hot has a vent that won't close. A radiator that's cold and has water pooling at the valve has a leaking valve, not a vent problem. Each one is a different small repair.
- •Cold + silent vent: vent stuck closed — replace the vent
- •Hissing + never fully hot: vent won't close — replace the vent
- •Cold + water at the valve: leaking valve — replace the valve
- •Cold on a whole floor: balance the vents, bigger vents on the top floor
Call and tell me which it is
Describe what the radiator's doing — cold, hissing, or leaking — and I'll tell you which part it is. Air vent replacement is a short, inexpensive job that turns a cold room warm again.
Have a plumbing issue right now?
Call and leave a voicemail — Bob calls back during business hours. For the fastest reply (usually within the hour), email him directly.