A house with radiators is heated by a boiler in the basement, and the system is either hot water or steam. The two behave differently and are fixed differently, so the first job is to work out which you have.
Which system do you have?
- Hot water: each radiator, or baseboard, has two pipes, and a small bleed valve at the top of one end. The boiler has a pressure gauge, and there is a circulator pump on the pipework near it.
- Steam: most radiators have a single pipe at the bottom and a bullet-shaped air vent halfway up the side at the other end. The boiler has a glass tube on the side that shows the water level.
Hot water systems
A radiator that is cold at the top
Air is trapped in it. Bleeding it takes two minutes.
- Turn the heating off and let the system cool for half an hour.
- Hold a cup and a cloth under the bleed valve. Open it a half turn with a radiator bleed key, or with a flat screwdriver on some models.
- Air hisses out. When a steady stream of water follows, close the valve.
- Start with the radiators on the lowest floor and work upward.
- Afterwards, check the boiler's pressure gauge. When cold, most houses need 12 to 15 psi. If it has fallen below that, the system needs topping up. If you are not sure how, ask a plumber to show you once.
One radiator that is cold all over
Check that its valve is open. If it is, the valve may be stuck, or that loop has an air lock, and a plumber can sort it out quickly.
Every radiator is cold
Check the thermostat, the boiler's power switch and the pressure gauge. If the boiler is running and the pipes near it are hot, the circulator pump may have failed. That is a repair for a professional.
Steam systems
A radiator that will not heat
- The supply valve must be fully open. On a one-pipe steam radiator, the valve at the floor is either all the way open or all the way closed. Partly open, it traps water and causes banging.
- Check the air vent. Steam cannot enter a radiator until the air gets out. If the vent is blocked with scale or has been painted over, the radiator stays cold. Vents unscrew by hand once the system is cool. Replacing one with a new steam radiator air vent is inexpensive. The numbers on vents indicate how fast they release air, so match the old one.
Banging pipes
The noise is called water hammer. Steam is hitting water that has pooled where it should have drained back to the boiler.
- Check the slope of the radiator. A one-pipe radiator must tilt very slightly toward its supply valve, so that water can run back out. Floors settle over the years. Put a level on top, and if it tilts the wrong way, raise the feet at the far end with thin shims.
- Open the supply valve fully, as above.
- Banging from pipes in the basement usually means a pipe has sagged, or the boiler's water level or pressure is set wrongly. That is a job for a plumber who knows steam.
A vent that hisses constantly or spits water
Replace it. If a new one does the same, the system pressure is probably too high, which a professional should adjust.
The boiler itself
Look at the glass tube weekly during the heating season. The water should be roughly halfway up. Many steam boilers have a low-water cut-off that needs to be flushed regularly. Ask your plumber to show you how at the next service.
Once a year
Have the boiler serviced before each heating season: cleaned, checked for safe combustion, and its safety controls tested. A carbon monoxide alarm on every floor is essential in a house with a boiler.
Leave these to a professional
- Any smell of gas: leave the house and call PSE&G or 911 from outside
- A relief valve that is dripping or discharging
- Pressure that keeps climbing, or keeps falling
- Water on the floor around the boiler
- A boiler that shuts itself down repeatedly
Find a licensed plumber, and ask whether they work on steam systems. Not every plumber does.