Steam or Hot Water
A boiler that is running has not always made heat the rooms can use. Steam and hot water move that heat in different ways, and the safe checks are not the same.
A steam radiator usually has one pipe and a small air vent on the end opposite the valve. Some steam radiators have two pipes and a trap. The boiler has a sight glass that shows the water line. A hot water radiator has two pipes and a small bleeder near the top. Its boiler has a pressure gauge and a pump, called a circulator, on the piping.
Every Radiator Stays Cold
If the boiler is hot and none of the radiators warm up, the heat is being made and not delivered.
On hot water, a circulator that is silent, or that hums while the supply pipe a few feet away stays cool, is not moving water. A zone valve that never opens does the same thing to every radiator on that zone. Air sitting at the top of the loop can block the upper floors even when the boiler is hot.
On steam, an empty sight glass means the low water cutoff has a reason to hold the burner off. If the glass shows water and the boiler is steaming, closed or painted main vents can keep steam from leaving the basement. A valve left halfway on a one-pipe radiator blocks that radiator. It does not, by itself, leave the whole building cold.
Only Some Radiators Stay Cold
If the rooms near the boiler are hot and the far rooms or the top floor stay cool, the boiler is making heat. The piping is not sharing it.
On one-pipe steam, the valve at each radiator is fully open or fully closed. Halfway traps water in the radiator and keeps steam out. A vent that is clogged or painted shut stops air from leaving, so steam never enters. Main vents that no longer open make the radiators closest to the boiler heat first and the ones at the end of a long main wait. A radiator that tilts the wrong way holds water. That water takes the space steam needs.
On hot water, one cold radiator with a warm bottom and a cool top usually has air in it. A whole floor that stays cold while the rest of the house heats points to that zone's valve or pump, not to every radiator in the building.
Checks That Stay on the Safe Side
Set the thermostat to heat, above the room temperature, and give the system time to respond. Confirm you are not looking at a boiler that is only making domestic hot water.
- On one-pipe steam, open a halfway radiator valve all the way, or close it all the way. Do not leave it between.
- Look at steam vents. If one is buried in paint, steam cannot push the air out. Do not unscrew a vent while the radiator is hot.
- If a steam boiler's sight glass is empty and the boiler is hot, switch the boiler off and let it cool. Do not pour water into a hot, empty boiler.
- On a cool hot water radiator, the bleeder near the top can release trapped air. Hold a cloth under it, open it slowly, and close it when water appears. Do not bleed a steam radiator.
- If the hot water pressure gauge needle sits at the bottom, the loop may not have enough water to reach the upper floors. Filling it over and over means the water is leaving. That leak is the repair.
Pumps, zone valves, main vents, and a boiler that keeps losing water are repair work. So is a steam vent that has to come off, and any piping that has lost its slope.
When the Burner Is Not the Problem
A burner that will not light, a lockout, or water on the floor is a different problem from radiators that stay cold while the boiler runs. That no-heat case is emergency boiler repair. If the house is heated by ducts rather than radiators, read why a furnace starts and then shuts off.
Walk-ups in West Farms and East Tremont are often steam. Houses in Van Nest and Crotona Park East may be hot water or a furnace. The repair either way is steam and hot water boiler repair across those neighborhoods and the rest of the Bronx. If the radiators are still cold after the checks above, call (914) 573-5224.