How to Fix That Knocking Sound Whenever You Flush the Toilet

August 6, 2020by Lasiter & Lasiter

The knocking sound that you hear when you flush the toilet may sound disastrous at first, but fret not. Usually, the cause behind this is not as complicated as you might have expected and simple steps can be taken to resolve it right away. 

The knocking sound you hear is actually a water pressure spike. Know that your toilet has valves that operate manually when you flush it, in which the water fill valve opens to let water into the tank to replace the outgoing water. Because of this, the water feed is always under pressure. When the valve is closed, the water in the pipe on the other side will be still but will remain under pressure. Once the valve is opened, the whole pipeline of water will rush forward toward the toilet tank with force.

So, when the automatic water valve of the tank shuts abruptly, the rushing water will have no place to go and will crash into itself, which is the knocking sound you hear. 

As you can see, the knocking is something you shouldn’t actually worry about, yet that doesn’t mean you should put it off. When it goes untreated, keep in mind that it could loosen pipes over time and that knocking sound will intensify. As a result, you will hear it more often, not only when you flush. 

Before the whole system blows over, it’s essential to resolve the issue right away. 

How to Fix the Knocking Sound

If you are familiar with plumbing systems, then the fix should be easy. However, if you’re not, there are still steps that you can take before calling in an expert to take care of it. 

The first step is to turn off the water’s main shut-off level and open the highest faucet in the house and drain water from the lowest faucet. After this, flush all the toilets in your house and run the dishwasher and washing machine for several minutes to drain them. Once you have drained all your plumbing system, close the lowest faucet and turn on your water supply. Keep in mind that the top faucet will spew out water before it gives off a constant stream. Once it does, turn it off and then flush the toilet that created the knocking noise again to see if the issue has been resolved. 

Yes, that’s all you need to do! There’s no need to take out the tools and get your hands dirty. However, if the knocking sound continues after the steps that you have taken, there may be other reasons for this, such as excessive water pressure in the pipes or loose pipes. Regardless of the reason, this is when you undoubtedly should seek the assistance of a professional to help resolve the issue. 


The knocking sound that you hear when you flush your toilet may not be a major cause of concern. However, if it happens frequently, there’s an easy way to resolve it by yourself. Yet, there are instances when it will not work due to other reasons, which is when you will need the help of a licensed expert to get the job done right. 

So, the next time you hear that knocking sound and are worried about its implications, you know the steps that you will need to take!

If you’re looking for a reliable plumbing company in Fort Worth, our experts at Lasiter are ready to assist. We offer quality and affordable plumbing services that cover the small or large plumbing project you are facing. Get in touch with us today to see how we can help!


Lasiter & Lasiter Plumbing

For more than 45 years, we’ve been serving Dallas – Fort Worth and surrounding communities with outstanding workmanship and high-quality plumbing services, at affordable prices, on each and every service call.

TX Master Plumbers Lic#: M-8331

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