The air filter is clogged: If the air filter for your heater is clogged, it may lead to the sound of hissing. What you are hearing is the sound of air forcing its way through a multitude of dust and debris. This is the easiest issue to deal with. Just make sure to change your filter every few months!
MY FURNACE IS MAKING A HISSING NOISE
If you're hearing a hiss, you're likely hearing escaping air. This could be caused by an improperly installed air filter, or one that is the wrong size. Often having too many closed vents, or having furniture blocking air flow can be the cause of a hissing sound.
Most radiators should be bled every year or so. Sometimes, the bleed valve will loosen itself, or someone might not have shut it tightly enough the last time they used it. Bleeding the radiator and closing the valve tightly should stop the hiss.
Any odd noise coming from a furnace, boiler, or heat pump could mean something in the system has malfunctioned and is in need of repair. While low humming sound is typical when heating systems operate, any sound that is not common coming from the furnace or heat pump could mean a problem is present.
Weird hissing sounds are caused by low pressure of cooling agent in system, and it is too low because something (like some connection o-ring seal) in system is leaking. Faulty seals must be detected and fixed, and then system re-filled. Another option, unplug conditioner pump connection and disable this system forever.
Condensation may cause sizzling and popping noises within the burner area during heating periods. Water hammer noises due to high water pressure in the home's plumbing system can result in leaking water heaters, banging water pipes and excessive wear on appliances.
Hissing Sound From Heater Core
Either way, if you can hear a hissing sound from the heater core then it's a problem that will need rectifying as soon as possible. Make sure you act quickly to prevent significant long-term damage being done to the engine.
Normal Furnace Noises
Sometimes there is a little bit of a pop or click as the furnace fires up, then the heating system settles into a dull hum as it runs. Think of it like the click you hear when you turn on the burner on a gas stove.
Loud Bangs, Rumbles, Knocks, or Booms
Loud noises like this are a sign of a build of gas in a furnace. The noise you hear can mean your heat exchanger is at risk of cracking. Even worse, it's a sign that something dangerous could happen if you continue to use your heater.
A common reason for furnace buzzing is a loose transformer box. A furnace transformer regulates the incoming voltage to an appropriate voltage for the furnace to use. This is more common after a new installation. With an older furnace, the transformer may be malfunctioning and needs to be replaced.
The air filter is clogged: If the air filter for your heater is clogged, it may lead to the sound of hissing. What you are hearing is the sound of air forcing its way through a multitude of dust and debris. This is the easiest issue to deal with. Just make sure to change your filter every few months!
When recording, you can eliminate the noise by removing noise sources such as a fan or a computer. You can also reduce the hissing sound by placing the microphone closer to the subject. Another way to eliminate hissing noise is to turn off the auto-gain settings in the camera.
If you notice your radiator making hissing noises, it's often a sign that the vent is obstructed and needs some care. The air vent may be clogged with rust, calcium buildup, or other debris, preventing it from functioning properly.
Tinnitus is one possible reason, but there are also myriad other causes of a hissing sound. Medical conditions like high blood pressure, reactions to medications, and injuries to the head and neck can also prompt a hissing noise or cause the perception of this sound.
Luckily, there's an easy fix to eliminate the sound or at least make it less noticeable. The noise is essentially caused by the heating element being installed on a wall that is warped or slightly uneven. To fix it, just readjust a few screws so the unit fits snugly against the wall without pinching the element.
This is a fairly common occurrence. When you use a large amount of hot water, the tank is refilled with cold water, which causes condensation to form on the outside of the tank. The condensation then rolls down and comes into contact with hot surfaces, like the area near the burner, producing steam and hissing.
If you hear a hissing noise, check to make sure that your furnace and vents are not being blocked by any objects or debris. In the case that it isn't, you'll need to call a furnace expert to check the situation out. The issue may also be an air duct leak or air filter blockage.
Pilot flame color changes
A yellow flame is a clear sign that the gas is not burning properly. Dirty or partially blocked systems can produce this. It's also another sign that a call to your trusted HVAC contractor is needed to save money and keep you a bit safer.
There are a variety of problems that can cause your furnace to produce loud noises. Types of noises such as scraping, banging, whistling, and popping may be a sign of a loose part, cracked heat exchanger, or dirty gas burners.
When your heater turns on, noises like popping and banging are normal. There could be a few reasons why heaters make this sound, like dirty burners that need cleaning, or an excessive amount of gas inside the chambers.
In most cases, the humming is normal and stems from the draft inducer motor or the furnace blower motor. The draft inducer motor hums or cycles on when the thermostat calls for heat. The blower motor hums as it cycles air through the property. It is possible the humming can stem from an electrical issue.
Sizzling: When you hear your water heater sizzling, it is often because the water leaks onto a burner. Along with a sizzling sound, another sign that your water heater is leaking is a pool of water at the base of the heater.
One of the most common signs is a lack of heat coming from the heater. If you turn on the system and don't feel any warmth, it's possible that the heater core is not functioning properly.
In most cases, these noises come from newer, high-efficiency furnaces. The high-efficiency furnaces vent exhaust fumes may produce condensation from moisture in the air that must be drained. When there's an issue in draining this condensation, it may cause gurgling, dripping, or other watery sounds.
Total Cost of a Heater Core Replacement
There's no way to put an exact number on the cost of this repair with such wide variability in price, labor times, and shop labor rates. If your heater core needs to be replaced, you should plan on, at the bare minimum, $800-$1000.