Your heating system uses forced water, which when heated up, expands. This expansion in a limited space, such as a pipe or radiator, can lead to a condition known as air-bonded piping. This can cause air bubbles to be trapped, resulting in a rattling or tapping sound in the pipes. Metal pipes can also make crackling, moaning, or gurgling noises as they heat up and expand.
This is because they rub on other surfaces, such as walls, floors, and supports. It's worth checking the pipe to make sure it's secured properly and can't move. This can resolve a lot of strange noises with your pipes. It is possible to slow down the pump, but one of the side effects of doing so is that it slows down the heating process. If the pipes have room to expand but are still making noise, place some light insulation around the pipe, as that should help limit movement and attenuate sound. If it is, turn your attention to the central heating pump; it may adjust too quickly and you may need to slow down. Another reason for rattling, clinking, and tapping noises in your heating system is that air bubbles get trapped in the water in your heating system.
If the pipe is already secured with pipe clamps, you may need to redirect it to stop the tapping and humming noises you hear. If the central heating emits a hum, one area to check is the central heating pump, as this is usually the cause of this type of noise in a central heating system. Lime can also get stuck in the boiler, especially inside the heat exchanger, and can cause a whistle known as “kettles”. A knocking sound, or gurgling sound like the one described above, could also be caused by a buildup of lime inside pipes and radiators. Therefore, it's possible that the sounds you hear in central heating are caused by that natural process. If you think water hammers are occurring and that water is reversing direction when you turn off a faucet, you may need a heating engineer to analyze the problem for you. The boiler problem is more common in hard water areas, where the boiler heat exchanger builds up lime that restricts water flow.
The heat exchanger heats up too much and ultimately expands causing the heating pipes to make loud noises.
