Boiler making hissing noises

Is your boiler making hissing noises? This sound resembles a kettle’s sound when boiling water on a stove and can keep you up at night wondering if you are in danger of an explosion or if the boiler is showing signs of old age. Various factors cause this problem, and knowing the root cause is essential to figure out the best solution forward.

Causes of Hissing Noises in a Boiler

The following are the main causes of hissing noises in a boiler:

Limescale or Sludge Build-Up

If you have an older boiler, limescale or sludge buildup in the boiler components might be the reason behind this whistling sound. Limescale buildup is common in areas with hard water; the calcium and magnesium deposits in the water settle in the boiler components over time, causing blockages. These blockages cause overheating and steam production, producing the hissing sound.

Solution

If you suspect limescale buildup is the culprit, you can fix the issue by removing the limescale/sludge buildup. You can do it yourself using store-bought anti-limescale solutions. However, a professional may do a better job, especially if the buildup is significant. A heating engineer will do a power flush using a pressurized water device to rid your boiler of unwanted debris.

Overheating

The best temperature to set your thermostat is usually around 65℃; below this value, bacteria will find a conducive environment to grow, while a higher value will raise your heating expenses and probably reduce the lifespan of your boiler.

As your boiler ages, the thermostat may start failing, causing the boiler to overheat. When a boiler overheats, the temperature and pressure valve opens to release the pressure to prevent the tank from exploding. This action causes the hissing sound.

Solution

To solve an overheating situation, check whether your boiler thermostat is functioning correctly and adjust the settings if need be. You may need to replace your thermostat entirely if it’s broken from old age.

Condensation

If you have a conventional boiler (tank water heater), the hissing noises may emanate from condensation. A conventional boiler has a hot water tank and a feeder tank. The feeder tank adds cold water to the hot water tank the more you use hot water.

For instance, if two people have a shower in your home and another person is running the dishwasher, the hot water runs out fast, and the feeder tank replenishes the hot water tank with cold water. As the cold water comes into contact with the hot tank, condensation produces a hissing sound.

Solution

While this cause is harmless and one not to cause concern, using a boiler big enough to accommodate your household’s hot water uses can fix it.

Leaks

Leaks from incorrectly installed pipework, corrosion, and too much pressure can also cause hissing noises from your boiler. The leak can be in the pipework, radiators, and near the boiler. While many have mechanisms that shut the system before it can pose a danger, you should contact a gas engineer immediately.

Solution

Find the source of the leak and repair it with the help of a professional. If the boiler is too old for repair, replace your old boiler with a new one.