Why is my radiator or baseboard heat not working?

What to know first

• Steam and hot water systems fail in different ways. A hot water radiator gets bled with a key; a steam radiator never does.
• How much of the house is cold tells you where to look: one radiator, one zone, or everything.
• Never add water to a hot boiler, and never cap or plug the relief valve or its pipe. Hot water and steam scald.
• A rotten egg smell, a CO alarm or CO symptoms means everyone outside first, then 911.

Do I have steam or hot water heat?

Look at the radiator pipes and the boiler gauge. The U.S. Department of Energy explains that a boiler heats water to make either hot water or steam, then sends it through pipes. Hot water baseboards are also called hydronic heat.

The radiator clues come from Castrads, a cast iron radiator maker: its one-pipe steam, two-pipe steam and hot water radiator pages. The Weil-McLain gas boiler user manual calls the steam boiler's glass tube a gauge glass, with the normal waterline halfway up.

Baseboards with no pipes and a thermostat in each room are probably electric; this guide does not apply.

Baseboard heat not working: one radiator, one zone or the whole house?

The pattern points to the cause:

1. The whole house is cold. Check the thermostat is on Heat and set above room temperature, then the boiler's power switch. Weil-McLain says the gas boilers in its user manual shut down if the air intake or vent is blocked, so if your boiler vents through pipes on an outside wall, check after lake effect snow that drifts have not buried them. Clear what you can reach from outside. If the boiler still will not fire, call: do not reset a lockout more than once.
2. One zone is cold. The rest of the house heats, so the boiler works. Check that zone's thermostat and batteries. After that, look for a zone valve that will not open or a stopped circulator, the pump that moves hot water through the pipes. Both are technician jobs.
3. One radiator or one run of baseboard is cold. On hot water, that is usually air. On steam, it is usually the valve or the air vent. Both are covered next.

How do I bleed a radiator safely?

Bleeding lets trapped air out so hot water can fill the radiator. The U.S. Department of Energy advises removing trapped air from hot water radiators once or twice a season, and calling a professional if you are unsure how. Weil-McLain lists air and low system pressure among the common reasons some radiators or baseboards stay cold.

1. Turn the thermostat down and switch the boiler off. Let it all cool: Weil-McLain warns of severe burns otherwise.
2. Hold a towel or a small cup under the bleed valve, a small square fitting near the top of one end of the radiator.
3. Fit a radiator key, or a flat screwdriver if the valve is slotted, and open it slowly, only a little. You will hear air hiss out.
4. Close it as soon as a steady stream of water comes out.
5. Do the same on other radiators that heat poorly, then turn the boiler back on.
6. Check the boiler gauge. If the pressure is below the range in your boiler's manual, or drops again after each bleed, stop and call. Do not add water yourself.

If you cannot find a bleed valve, do not open any other fitting: call. Castrads notes that regular bleeding should not be necessary, and that frequent bleeding may point to a problem in the system. Weil-McLain lists leaks as the cause of a boiler that needs frequent makeup water.

Why is my steam radiator cold?

On steam, a cold radiator usually means steam cannot get in or air cannot get out. Check these, with the system off and cool:

• The supply valve. Castrads says a one-pipe steam radiator valve must be fully open or fully closed; half open causes noisy steam hammer.
• The air vent. It lets air out as steam arrives and closes when the radiator fills with steam, Castrads explains, and the heat a one-pipe radiator gives is controlled by how much air can leave. A vent stuck shut keeps steam out. Have it checked rather than forcing it.
• The pitch. Steam turns back to water in the radiator and drains back through the same pipe, Castrads says. The Hoffman Specialty steam heating manual shows one-pipe radiators pitched down toward the supply pipe for that reason. One that tilts the wrong way can trap water. Ask a technician to adjust it.
• The water level. Check the gauge glass from a distance. Weil-McLain's low water cutoff shuts the boiler off when the water drops. Leave adding water, draining and testing the cutoff to a technician, and never add cold water to a hot boiler: Weil-McLain says the thermal shock can crack the heat exchanger.

Why are my radiators or pipes banging?

In steam systems, banging is usually water hammer. Hoffman's manual says banging in steam pipes is usually steam collapsing in water lying in low points, cured by better pitch, support or drainage: technician work. Castrads also ties steam hammer to a half open radiator valve.

On hot water, Weil-McLain lists air as a common cause of noisy radiators, fixed by bleeding. A popping or percolating boiler can mean mineral deposits inside, Weil-McLain says: a technician job.

Is my boiler pressure too high or too low?

The gauge tells you, and your boiler's own limits are in its manual. For the gas boilers in its user manual only, Weil-McLain says the reading should not exceed 24 psig (pounds per square inch on the gauge) on a hot water boiler or 15 psig on a steam boiler. Other boilers can differ.

• High pressure on hot water: Weil-McLain points to the expansion tank, the tank that absorbs water as it heats, or the gauge.
• High pressure on steam: it points to the gauge or the limit control. If either stays high, it says to call a technician.
• Low pressure on hot water: Weil-McLain's fix is refilling to the correct pressure and checking for leaks. Have a technician do both.
• A relief valve that drips or discharges: call. Weil-McLain says a valve that often weeps may mean the expansion tank is not working on hot water, or a limit set too high on steam.

Never cap, plug or remove the relief valve or its discharge pipe. Weil-McLain says the discharge line must run to a safe place, because what comes out can scald.

Boiler vs furnace: what is the difference?

A furnace heats air and blows it through ducts; a boiler heats water and sends hot water or steam through pipes, the DOE explains. Its Energy Saver guide adds that boilers feed upright radiators, baseboard convectors or radiant floor tubing, and suggests considering replacement when a furnace or boiler is more than 15 years old, needs frequent repairs while energy bills climb, or leaves some rooms too hot or too cold.

What should I never do around a boiler?

• Smell rotten eggs or sulfur? That can be gas. Get everyone out first. Do not use a light switch, phone, flashlight, lighter or garage door opener inside, and do not try to relight anything. Enbridge Gas Ohio says to call its 24 hour line at 1-877-542-2630 or 911 once you are safely away. On another gas utility, call its emergency line or 911.
• Carbon monoxide has no smell. The CDC lists headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion. Symptoms alone, alarm or no alarm, mean what the U.S. Consumer Product Safety Commission advises: get outside to fresh air, then call 911. A sounding CO alarm means the same, Enbridge says. CPSC wants CO alarms on every level and outside sleeping areas.
• Standing water: go to the boiler switch or the electrical panel only if you can reach it without stepping into water near outlets, cords or the panel; otherwise stay out and call for help. Ready.gov warns not to touch electrical equipment if it is wet or you are standing in water. Weil-McLain says not to operate a boiler whose burner or controls were sprayed or submerged until it is repaired and inspected or replaced: do not relight, restart or reset it until a technician has checked it.

When to call Raber HVAC

• No heat in freezing weather: call (216) 888-4822 on our 24/7 emergency line. Weil-McLain warns that a boiler failure in cold weather can freeze plumbing within hours; our frozen pipes guide covers what to do. While you wait for heat, use only an electric space heater: the U.S. Fire Administration says to plug it straight into a wall outlet, never an extension cord or power strip, keep anything that can burn 3 feet away, and turn it off when you leave the room or go to bed. Never heat with a gas oven, camp stove, generator, grill or patio heater indoors or in the garage, as the CDC and Enbridge warn.
• A cold zone, a dripping relief valve, pressure outside its range, or banging that will not stop: call the office, open every day 8:00 AM to 10:00 PM. We work on cast iron and high efficiency boilers, circulators, zone valves, expansion tanks and radiator balancing. What a yearly check covers is in our tune up guide.
• Anything that can wait a day: book online, pick a day and an arrival window, and the office calls to confirm.

Sources

• U.S. Department of Energy, Home Heating Systems fact sheet
• U.S. Department of Energy, Energy Saver Guide: Tips on Saving Money and Energy in Your Home (2022)
• Weil-McLain, Gas-Fired Boilers User Manual (CGa, CGi, EG, PEG, LGB)
• Castrads, One-Pipe Steam Radiators and Valves
• Castrads, Two-Pipe Steam
• Castrads, Hydronic Hot Water Radiators
• Hoffman Specialty (Xylem), Steam Heating Systems Technical Manual TES-375A
• Ready.gov, Floods
• Enbridge Gas Ohio, Smell Natural Gas? What to Do Right Away
• Enbridge Gas Ohio, Carbon Monoxide Safety
• CDC, Carbon Monoxide Poisoning Basics
• U.S. Consumer Product Safety Commission, Carbon Monoxide Information Center
• U.S. Fire Administration, Heating Fire Safety handout