The Kingspan quick guide to water hammer and how to fix it

15 April 2019 Kingspan Water & Energy

Does your customer’s plumbing system have more banging than Phil Collins’ drum kit? Our water hammer guide is just what you need to diagnose and stop this surprisingly common problem.


What is water hammer?
Let’s face it, the last thing you want as an installer is to be on the receiving end of a phone call asking you back to a job because, “my heating pipes are making a loud banging noise!”
Boilers, unvented cylinders and water heaters are often unfairly scapegoated as the source of the noise, when the real problem is water hammer. The problem is so common that if you type, “How do you stop water pipes from banging?” into Google, you get over 600,000 results!
What causes water pipes to hammer in the first place?
Water hammer is caused when moving water comes to a sudden stop. This creates a shockwave travelling through the plumbing system, and it’s this shockwave that makes the noise.
Shockwaves can be caused by a tap being quickly switched off or a valve being closed. This makes the water come to an abrupt halt, so it then tries to move back down the pipework. If the water then hits another stop in trying to find a way out, such as a closed check valve, this can cause a (noisy!) shockwave up and down the pipe.
The problem of banging pipes can be made worse if there’s a build-up of limescale in the pipework, as the water has even less space in which to manoeuvre. That’s more likely in hard water areas.
Can water hammer result in any other problems?
Noisy pipes may be a nuisance, but water hammer can cause more serious problems.
With shockwaves bouncing back and forth along pipework in the style of an Andy Murray rally, water pressure increases.
Left untreated, water hammer can lead to actual damage to pipework, appliances and components of any system. Over time this damage can accumulate and result in the premature failure of parts of the plumbing system and all the watery hassle that can cause.
Limescale simply exacerbates the problem, as our water quality blog will testify.
How do I get rid of water hammer?
Although it’s not always completely fixable, those noisy pipes can definitely be tamed with a bit of good plumbing practice.
As a starting point, it’s worth making sure pipes have been installed with enough pipe clips, and that non-return valves haven’t been locked.
Next up, it’s time to tackle the problem of the increased water pressure. This can be fixed by retrofitting a water hammer arrestor. The arrestor acts like a mini expansion vessel and gives the pressurised water somewhere to go, thereby reducing the pressure. Lower pressure equals less hammer-like noise!
And to finish up, if there’s a chance that limescale could be making the problem worse, then water softeners can help clear that calcium away!
Summing up
Water hammer is no exception to the old adage that prevention is better than the cure. With good plumbing practice, a shock arrestor, and a descaling maintenance routine where needed, any Phil Collins’ drumkit-style banging can be reserved for the next 80s revival gig.