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Pipes Knocking When Hot Water is Turned On

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Banging noises from water pipes is a common phenomenon, particularly in outdated homes. The knocking noises can irritate you and other house occupants, especially when it's been going on for a while. It is time to consider repiping for you to get rid of this knocking noise for good.

The problem might be simple for you to handle, but it is advisable to get recommendations from a plumbing expert like Plumb Guardian. A plumber can efficiently address and solve the issue at hand better than you. 

Related article: water pipe noise when water is not running

Related article: water noise in pipes

Why Do Pipes Knock When Hot Water is On?

The knocking sound that begins immediately after turning on a hot water tap can be the reason for the expansion and contraction of the CPVC pipes in your home. If the CPVC pipes lack adequate room around, it produces knocking sounds.

Everyday situations that indicate poor construction of CPVC water lines:

  • Light cream-coloured piping running to your hot water appliances.
  • Knocking sounds when a hot water tap is switched on.
  • The noises stop after the hot water tap is switched off.

5 Reasons Why Your Plumbing Pipes Make a Knocking Noise

The Chlorinated Polyvinyl Chloride (CPVC) piping within the home walls starts to expand and contract whenever the hot water passes. Sometimes, you may begin to hear knocking noises immediately after switching on your hot water faucet. 

Below are some of the problems you are likely to encounter that results in the aggravating banging noises:

Blockages that Cause Sludge Build Up

Gradually, the wear and tear chemical processes occurring within the pipework builds up debris. The debris slows the draining water in the central heating systems creating sludge. Sometimes, it accumulates and circulates through the supply pipes, causing water hammering.

Putting up with the banging and rattling knocking noises is a pain in the neck. However, don't try to attempt draining the water lines by yourself. Instead, reach out to a plumber to get it fixed with a power flushing service.

High Water Pressure Causing Noisy Pipes

If the water pressure is excessively high, the CPVC piping will produce a knocking sound. The water pressure should range between 1 to 1.5 bar. Anything above this will increase water's flow rate, overwhelming your pipe systems.

Ensure you look at the boiler's water pressure test gauge and adjust the regulator to the correct pressure level. It is a straightforward solution to stabilise the pressure by consulting your meter manually. If you don't have a regulator, then you should reach out to a plumber.

You might need to turn the temperature levels down. If that is not the case, think about installing a water heater tank to suck up high water pressure.

Water Hammer

As time goes on, water banging into valves can result in potential damage unless someone fixes this.

In due course, water starts replacing the air reducing the stopping power of the air chambers. The air chambers are usually fixed adjacent to water taps preventing water from banging into valves when taps are not running. Rushing water slamming into the valves results in that banging noise.

If your home is old, air chambers installed can be filled with water when all faucets are running. You will drain the excess water later from your pipes. Modern homes are set up with water hammer arrestors that absorb the shock when the valves shut off.

How Do You Fix a Water Hammer?

  • Switch off your main water supply
  • Startup the taps on the peak of your home
  • Switch on the taps on the base of your home
  • Allow all the excess water in the valves to drain from your pipe system.
  • After draining the water, turn the water supply back on.
  • Allow the water to drive away any air within the pipes by ensuring all taps are running until all excess water comes out.
  • Disconnect the taps

The air chambers will now be restored with the air needed to act as shock absorbers. It will also eliminate the knocking noise. We recommend you consult expert plumbers if this doesn't work for you.

Loose Fittings in Plumbing Pipes

Over time, the pipes supplying hot and cold water to your faucets like in a laundry room, toilet, or shower might become loose due to friction. You will then start to hear banging and rattling sounds from your pipes. You can get rid of the knocking noises by foam insulation at the beginning and end of the pipe.

The plumbing service could be the reason, especially if the plumbers you hired couldn't fit the pipes properly. If you can reach the loose pipe, you can replace or buckle the straps by yourself. However, if the problematic pipe is out of your reach, we recommend professional plumbing help.

Copper Pipes

Most plumbing pipes used in homes are made of copper. Copper is a durable and malleable metal that can be used instead of steel and lead in the modern generation. If your water tap is running hot water, the copper will expand. The expansion and contraction of the pipe cause stress within.

The abrasion and friction resulting from expansion cause the pipe to rub against joints producing a knocking noise. However, you can handle the noise by:

  • Insulating the pipe with foam rubber to avoid friction against other surfaces in your home.
  • Lowering the temperature of hot water to reduce the expansion of the metal.
  • Reaching out for professional help if the problem is extreme.

How Do You Stop Your Hot Water Pipes from Knocking?

Does your home have old pipes? It is time to think about fixing and installing new pipes. Outdated homes are likely to experience water hammering issues. This is due to malfunctioning air chambers. We highly advise you to hire a professional plumbing service team to upgrade the air chambers or install water hammer arrestors.

If you notice your pipes are pounding against the inside of the walls, it results from expansion and contraction as hot water runs through. You can avoid this by spotting the malfunctioning pipe and cover insulating foam at the grinding end.

High water pressure increases the rate of water flow within your pipes. When water bangs through the pipework plumbing system, rattling and banging sounds come out. However, you can fix this by using a simple water pressure test gauge. Ensure there is no water tap running in your home. Turn on the spigot and make sure the water pressure reads 40-80 PSI.

The most common reason for the rattling sounds is when sludge builds up in your water heater. The sounds come from the steam bubbles finding their way through the sludge. Contact your plumber to fix the problem, or you can flush the sludge yourself.

Bear in mind that if the situation at hand is extreme, do not take matters into your hands. Contact a plumbing team to diagnose where the problems are.

Wrap Up!

Are you worried about where to get a professional plumber? Well, don't worry anymore. Our plumbers provide the best plumbing service to meet your deadlines. We guarantee 100% satisfaction if you're experiencing a plumbing emergency.

Our heating engineers are available 24/7 hours a day, seven days a week. Reach us today, and we'll schedule an appointment for you as soon as possible.


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