Water Hammering

water hammer in the tap

What is a water hammer?

Did you know that a water hammer in the plumbing system can cause banging noises even after the tap being turned off? It is time to investigate before any serious plumbing issues arise.

The banging noise is the pipeline is moving between the joints, touching each other or hitting the wall.

Why do you have a water hammer?

The water hammer is caused by the mains cold water by putting pressure on your plumbing system. In simple therm the high water pressure flowing in your pipeline, and when you close your tap this pressure creating a shock wave and making noises.

If you hear this BANGING noise for the first time, you will not recognise it. Your pipework starts to rattle. But you cant decide if the noise came from the roof, from inside the walls or under the floor. This loud banging noise is called water hammer or other names hydraulic shock.

These are a few sources that can cause water hammer:

  • Air in the system
  • Losen pipework
  • Ball or float valves are faulty
  • Solenoid valves
  • Stopcock
  • Washing machine valves
  • Fit a pressure reducing valve
  • Taps and outlets

Why do you have a water hammer or hydraulic shock?

There are many reasons we have to talk about. Water hammer occurs when the water in your pipes changing direction or something stopping the water flow instantaneously. Normally you hear this BANG when you close your kitchen tap or closing the shower mixer. When you close one of the taps the pipework banging against the wall or hitting each other.

Another time the water hammer could occur is during the night. When no one using the water in your streets, the water pressure increases in your home and rattling. The best thing to start with is to fit a pressure reducing valve before the cold water enters the house.

If you think that this water hammer will suddenly go away in a few days, we have to disappoint you, because it will just get worst. It can cause water leaks and damage to your property.

What can cause a water hammer?

1. Air pockets in the system?

Don’t mix an air pocket with an airlock in the system. An airlock will sully stop the water flowing into your taps.

Air pockets can cause a banging sound. But this is happening straight after you open one of the taps. The air starts to flow with the water and hitting the pipe wall making a noise. To remove the air pocket you have to flush through the system properly and in some cases, the pipe needs to be cut so the air can be released and the system flushed. Installing automatic air vent valves can prevent water hammers. This can be installed at the highest point where the pipework is running.

An example where you can fit the automatic air vent is the hot water cylinder highest point of the water supply pipe that feeds the taps. After you have done any plumbing job, make sure you fill your system slowly to prevent air trapping in the pipes. Also, open the taps to release the air from the system.

2. Washing machine valves

washing machine isolation valve

The washing machine valves can cause a water hammer! How? The valve can close very quickly and stopping the water flow. In simple terms the water hitting the valve inside the wall and making the bang. You can try to turn the valve by half turn and this can release some pressure. This is not the best solution but only for a DIY option. Another option is you increase the washing machine water inlet pipe size. The water will slow down in a bigger size pipe.

3.Fast Closing Solenoid Valves

These valves are operating electrically and closing the water instantaneously. This is a shock to the pipework causing water hammer. An easy DIY solution is to fit a flexible pipe in the pipes that can absorb the pressure change. A proper fix for this job will be an expansion vessel installation.

Are you asking where can you find a solenoid valve on your property? Well, dishwashers and washing machines are operated by a solenoid valve. When the appliance needs a water supply, the board is sending a signal to the valve to let water in or close it immediately.

4. Water hammer arrester

water hammer arrester

Sometimes it works. We can not leave it out from our guide. It works but it is not the best option. We speak from experience when we fitted a water hammer arrestor and didn’t work. It only works if the problem is not so bad. We are rather put an expansion vessel for a long term solution.

5. Pipework is not secured

pipe clips

Old plumbing systems in the UK are not secured, especially under the floorboard. This is one of the biggest factors when you realise you have a water hammer, pipes are hitting each other. To fix this it is an easy job by fixing the pipework with clips to the wall. The hard part is that sometimes you have to cut up the floorboard and climb underneath. Same option if the pipes are banging inside the wall. The wall needs to be cut and pipes need to be fixed.

6. Pressure reducing valve installation

pressure reducing valves

This is the best option to start to fix the problem to reduce water hammer. Fit a pressure reducing valve on the main water supply pipe, before the water reaching the appliances. Don’t forget to also install a stopcock before and after the reducing valve just in case if you have to replace the valve in the future you can do it in 5 minutes. While you doing this installation, you can also fit a limescale reducer.

7. It can be the tap

Old taps where you had to turn the handle two times before the water shut off it is less likely to cause a water hammer. It is because the water can drain from the system and slow down while you turn the tap off. Modern mixer tap turning off quickly and the water hitting the tap body making noises.

8.Your air chambers is blocked

You can see this in the modern water system. You might don’t have this in your system so don’t start to look for it. This air chamber helps to reduce the shock wave in the pipework after you close the tap. When the air chamber starts to fail, the water will replace the air and causing water to hammer. If the air chamber is not blocked, then you can easily shut off the water, drain the system by opening the tap, and the air chamber will fill up with air again.

9.Old stop valves

Your 15-year-old stop valve can also cause this noise. This can happen when the stop valve has loosened washers glands. The water flowing through the valve and rattling the handle.

10.Water tank ball valves

Water wave? Have you heard about this? Your water tank in the loft starts to fill up, the ball valve is starting to closing. But sometimes the ball valve (what is controlling the water pressure) is closing, falling, opening-closing again. If you have only a plastic water tank the water will make waves and pushing up and down the ball valve and cause a water hammer.

If you install a water pressure reducer this will help you maintain the constant pressure in the whole water system. Make sure you install a plastic water tank that is reinforced by a metal frame.

How to fix a water hammer?

  • Make sure all your pipework are fixed properly to the wall and floors.
  • In some places, you have to fit a copper pipe expansion joint, this will prevent water hammer.
pipe expansion joint
  • Install a water hammer arrestor. But our best advice is to always fit a potable water expansion vessel on the pipework. The expansion vessel can deal with higher water pressure and you can avoid banging noises.
  • Fit a pressure reducing valve.
  • Use pipe insulation around the pipes which can absorb the water hammer and pipe expansion. Pipe expansion happens when cold or hot water flowing in the pipes and increasing the pipework by a few centimetres or meters depending on the pipe materials.
  • Sometimes just leave the job for the professional plumber
  • Choose a solenoid that is closing slowly.
  • Install a water pressure regulator

You can install a copper air chamber.

The idea behind the air chamber is when the water is suddenly shut, this air chamber will absorb the high pressure.

Install a mechanical water arrestor

The shock arrestor is working similar to the air chamber but the spring reducing the shock wave. This is. more expensive to install but it will help to resolve the issue.

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Frequently Asked Questions About Water Hammer

Q: How do you fix a water hammer in the shower?

  • Avoid air getting to the system.
  • Install a pressure reducer.
  • Change all the faulty cartridges
  • Clip water pipes
  • Use pipe

Q: How do I get rid of the air in my water pipes?

Sometimes it is enough if you open the tap and showers and run it for few minutes. The air should leave from the pipes

Q: What causes water hammer noise?

Usually, a water hammer is caused by the high-pressure incoming main water supply causing a water hammer. This putting pressure on your water system.

Q: Can a toilet fill valve cause a water hammer?

In short yes. If you have a faulty inlet valve with limescale build on it this can not close fully when needs and can cause a water hammer.

Q: Can water hammer damage pipes?

In the short run NO. To stop the water hammer in your plumbing, you must first diagnose where it is coming from and then repair that problem. In the long term, water hammers can damage the joints in the water system, causing them to leak.

Q: How much does it cost to fix the water hammer UK?

You cant get an exact price for this work. The plumber needs to investigate the job first. This can be 1 hour to a few hours. If the nagging noise came from under the floorboard, this needs to be searched first.

Q: Do I need a water hammer arrestor for a shower?

You only need a hammer arrestor if you hear the banging noise that is coming from or around the shower.

Q: How do I stop my house pipes from banging?

The best solution to start with is to install a water pressure reducer and an expansion vessel to the main water supply pipe.

Q: Is the water hammer dangerous?

In a short period, a water hammer is acceptable. But in the long run, it can cause all kinds of cracks on the pipework and leaks.

Q: How to get rid of the water hammer?

If you carried out all the necessary steps and you still can’t find solutions then call a professional plumber who can provide solutions for your problems.



Do you fix you water hammer issues?

If you need to speak with our professional team call MML Plumbing at 02083550840 or you want to book our professional plumber contact us in North London today and we find the solutions for you!

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