Boilers and Radiant Heat

Boilers and radiant heat give many homes quiet, even warmth without blowing air around. They're common in older homes in colder parts of the country and in newer homes with in-floor heating. Here's how these systems work, what tends to go wrong, and how to keep yours running.

How a boiler system works

A boiler heats water, or in some systems makes steam, and circulates it through the house. The heat moves into rooms through:

• Radiators, the classic cast-iron units
• Baseboard convectors, the long, low units along walls
• Radiant floor tubing, embedded in or under floors
• Fan coils or air handlers in some combined systems

Hot water systems are the most common today. They use a circulator pump to move water through a closed loop, with an expansion tank to handle pressure changes as water heats and cools. Steam systems, found in many older homes, work differently and need their own care.

Types of boilers

You may hear these terms:

• Conventional boilers. Often cast iron, durable and simple.
• High-efficiency condensing boilers. Capture extra heat from exhaust gases. They produce acidic condensate that drains away, and they often vent through plastic pipe.
• Combi boilers. Provide both space heating and on-demand hot water.
• Fuel types. Natural gas, propane, oil or electric.

Common boiler problems

Watch for these signs:

• Low pressure. Many hot water systems have a pressure gauge. A reading that keeps dropping may point to a leak or a failing valve.
• Radiators cold at the top. Often trapped air that needs bleeding.
• Banging or gurgling pipes. Can mean air in the system, pressure problems, or, in steam systems, water trapped in pipes.
• No heat or uneven heat. Could be a thermostat, circulator pump, zone valve or control issue.
• Pilot or ignition problems. The boiler tries to light but fails or shuts down.
• Water around the boiler. A sign of a leaking valve, pump seal or the boiler itself.
• Condensate line blockage on high-efficiency units, which can cause shutdowns, especially in freezing weather.

If you ever smell gas, leave the house and call your gas utility from outside.

Radiant floor heat specifics

Radiant floor systems are comfortable and quiet, but repairs can be harder:

• Tubing is usually buried in concrete or under flooring, so leaks can be tough to reach.
• Mixing valves and manifolds control water temperature and flow to each zone.
• These systems respond slowly. Big thermostat swings can make them feel uneven.

A technician familiar with radiant systems is worth finding before you need one.

Basic upkeep

A few habits help your system last:

1. Schedule annual service before heating season. A technician can check combustion, safety controls, the expansion tank and venting.
2. Bleed radiators when they're cool at the top.
3. Watch the pressure gauge and note what's normal for your system.
4. Keep the area clear of storage and flammable items.
5. Install carbon monoxide detectors near sleeping areas and on each level.
6. Check steam boiler water levels if you have one, following the manufacturer's instructions.

How home warranties handle boilers

Many home warranty plans include boilers as part of their heating coverage, often covering parts like circulator pumps, burners, gas valves, igniters, thermostats and zone valves. Coverage limits, exclusions and caps vary.

Common limits include:

• Radiant tubing embedded in floors or concrete may be excluded or limited
• Radiators and baseboard units may be treated differently from the boiler itself
• Rust, sediment and corrosion damage may be excluded
• Code upgrades or venting changes may have caps
• Problems from lack of maintenance may be denied

Ask how the plan handles distribution piping, and check the caps. Our page on plumbing coverage can help you see where some piping falls.

How Warranty Wizards can help

We help homeowners compare home warranty plans from independent third-party providers and explain how each plan covers boilers and radiant systems before you buy. Get a free quote at get a quote.