Common Boiler and Furnace Issues

Neil Burtt
7 hours ago
5 min read

A man wraps himself in a cozy blanket because his home is experiencing some heating issues.

Brrrr. Fall is here in New England, and as the temperatures continue to drop, many homeowners are waiting for just the right moment to turn on their heating systems. Now is a good time to familiarize yourself with the type of system you have and learn how to identify and troubleshoot the most common heating issues.

Boiler (Forced Hot Water) vs. Furnace (Forced Hot Air) Heating Systems

How do you know if you have a boiler or a furnace? A boiler heats water and

sends it through pipes to radiators or baseboards to warm your home. A furnace

heats air and uses a blower to push it through ducts and vents. Below are common issues with each type of heating system.

Common Boiler Issues

1. Leaks

If your system is leaking, it means that water is escaping somewhere—either from the boiler itself or the connected pipes, valves, or fittings. This can cause severe water damage to your home and may signal an underlying issue, such as:

● Excessive System Pressure

● Corroded Pipes or Tanks

● Faulty Pressure Relief Valve or Other Component

● Damaged Seal

If you notice a leak, turn off the boiler and power supply and contact a licensed HVAC professional, like Main Stream Mechanical, to inspect the system. A trained technician can pinpoint the source, safely repair or replace components, and ensure your heating system operates efficiently and safely again.

2. Hot Water, But No Heat

If you have hot water but no central heating, here are some common causes:

Improper Settings: Make sure your boiler temperature isn’t set too low or configured for “hot water only” (common in the summer). Also, check the timer settings for the heating program.

Faulty Batteries: Low batteries can prevent the thermostat from signaling the boiler to heat your home.

Low Boiler Pressure: If the pressure is too low, the system won’t be able to circulate hot water through the radiators or baseboards.

Circulating Pump or Relay Issues: If the circulating pump is faulty or the relay controlling it has failed, your system won’t move hot water to the radiators/baseboard, and your home will not warm up.

Trapped Air in Radiators: This can block the flow of hot water. Bleeding your radiators will remove the air and keep your system running efficiently.

3. Boiler Kettling

Kettling is a term used to describe the rumbling, banging, or whistling noises

emanating from a hot water boiler. It happens when limescale builds up on the

heat exchanger. This buildup causes water to boil and steam to form inside the

boiler, leading to the strange noises you hear.

It’s most common in areas with hard water, but it can occur anywhere if the system isn’t regularly maintained.

The best solution is to contact a licensed HVAC professional, like Main Stream Mechanical, to inspect and flush the system. We will remove the

buildup, check for underlying issues, and help prevent future damage.

4. Frozen Condensate Pipe

Every condensing boiler has a pipe that carries wastewater, a byproduct of the

boiler’s operation, from the unit to a drain. When temperatures in an uninsulated location drop below freezing, the water inside this pipe can freeze and block the flow, causing your boiler to shut down as a safety measure.

5. No Hot Water OR Heat

Your boiler may stop providing hot water or heat for several reasons:

It is disconnected from the power, gas, or water supply; either switched off

accidentally or from a power outage.

The system is turned off because the boiler pressure is either too high or too

low.

There are piping issues, such as frozen condensate (described above) or

an airlock.

Tip: If you see an error code, write it down for the service technician to reference when assessing your boiler system.

Common Furnace Issues

1. Wrong Thermostat Setting

Sometimes the thermostat is simply in the wrong mode; for instance, it is switched to “cool” or “off” instead of “heat.”

Tip: Ensure the fan is set to “auto” not “on.” Adjust the thermostat so it’s in heating mode and set higher than the current room temperature.

2. Clogged Air Filter

A dirty air filter restricts airflow, which can cause the furnace to overheat and

automatically shut down as a safety precaution.

Tip: Check your filter quarterly, and replace it if it appears excessively dirty or caked with debris.

3. Closed or Obstructed Vents

Make sure all vents and registers throughout your home are open and free of

obstructions like furniture, curtains, or rugs that can block air circulation.

4. Overheating System

Several mechanical issues can cause a furnace to run too hot. In this case, the high-limit safety switch will turn the unit off to protect it from damage.

5. Ignition Failure

Furnaces with an electronic ignition system may develop issues if the ignitor

becomes dirty or wears out. If cleaning doesn’t resolve the problem, contact our

HVAC experts so we can replace the component.

6. Contaminated Flame Sensor

The flame sensor ensures gas is only released when a flame is present. If the sensor becomes coated with debris or corrosion, it may falsely detect no flame and shut off the gas supply for safety.

7. Fuel Supply Issues

Natural Gas: Contact your gas utility to verify there aren’t any service

outages.

Propane or Oil: Check your tank level to confirm there’s sufficient fuel for

operation.

Tip: Don’t let your oil tank level dip below ¼ full to avoid pulling sludge into the fuel line.

8. Blower Motor Malfunction

The blower motor is responsible for pushing warm air through your ductwork. If it stops working, the burners may still ignite, but no warm air will reach your vents.

You might hear the furnace running, but only feel cool air.

9. Electrical Problems

A tripped breaker or blown fuse can cut power to your furnace. Inspect your

electrical panel and reset any tripped breakers. If it trips again, call for professional

service.

10. Defective Gas Valve

A dirty or worn gas valve can prevent fuel from reaching the burners, keeping your system from heating correctly.

The Benefits of Regular Heating System Maintenance

Whether you have a furnace or boiler system, the best way to keep it running safely and efficiently is with annual heating maintenance. Having an HVAC professional inspect, clean, and tune up your system each year helps catch early signs of wear, extends the life of your equipment, and ensures your home stays warm and reliable through every New England winter. Contact us today to schedule your appointment.