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Why Does My Bunn Coffee Maker Overflow?

Your coffee machine can determine if you’re going to have a good day or not.

And a brewer that produces great coffee and works as expected is crucial to getting your morning right.

I don’t know about you, but an overflow of coffee or water from my coffee machine is the last thing I want to see in the morning.

Especially before having my morning cup of brew.

But like with most inventions, Bunn coffee machines are not immune to mishaps such as the occasional overflow.

If this happens, it could mean a bad start to your day or a replacement of your coffee machine in the worst-case scenario. 

In this article, we will be looking at coffee machines and some of the reasons why your Bunn coffee machine could be overflowing.

So keep on reading to find out more.

Excess Ground Coffee

Overfilling your brew funnel with coffee past the recommended amount means you have to compact it tight to close the rid.

Compacting coffee grounds reduces the air and the number of open pockets in the ground that allow water to flow through into the jag. 

And if water, or in this case coffee, can’t flow down to the jag, it collects up in the brew funnel and overflows.

Simply using the right amount of coffee ground in your brew funnel can mean the difference between an overflowing coffee maker and one that functions normally. 

Too finely ground coffee beans

With coffee machines, it’s all about having a flow of hot water through the coffee grounds, down to the jag.

And just like in compacting your grounds, too finely ground coffee beans also reduce the spaces between them and block the flowing water paths.

This block leads to a build-up of water in the brew funnel.

Eventually, the water will overflow when the rate of water coming into the filter gets higher than the rate of water flowing out of the brew funnel.

Using coarsely ground coffee beans can help alleviate this problem because they have more open spaces that let water flow through easily than finely ground coffee beans.

Poorly Sealed Basket

A poorly sealed basket means your Bunn coffee machine is not water-tight enough to prevent leaks or overflows.

This could be down to poor product quality checks by the manufacturer, and your unit lacks some seals that help prevent leaks and overflows.

Or it could be a badly closed basket by a user after cleaning or maintenance.

And it goes without saying if your unit lacks waterproof seals or the basket is not correctly closed, then add water into the coffee machine; it’s going to leak out.

So, next time you find your coffee maker has overflown, first check to see if the basket is correctly closed and that all the seals are intact before checking for other defects or causes.

The type of filter you are using

I know most will roll their eyes at this one, but each manufacturer makes their machines with particular filters in mind.

Manufacturers like Bunn have to make and test their machines in a certain way.

And that means they have to decide what type of filters they want to use when designing and making a coffee machine.

Which differentiates how particular units perform and the type of brew they make.

And as such, only certain types of filters work best with particular machines.

And if you use a filter that’s not theirs or one that’s not recommended, it may not perform as expected and lead to an overflow.

Or even worse, lousy coffee. 

If you use Bunn’s filters and still experience overflows, regularly change them and discard used coffee grounds after use because that might also be the problem.

But using the manufacturer’s recommendations on how to operate your Bunn coffee maker is an excellent way to avoid overflows.

Brew volume

Every Bunn coffee maker comes with a brew volume knob that helps you set a brew amount.

And setting this volume to an amount higher than the jag can hold will lead to a fill-up and eventually an overflow.

The best way to avoid this type of overflow is by checking the capacity of your jug and setting your Bunn coffee machine at this volume or slightly lower.

Most don’t know that a Bunn coffee machine comes with a reserve tank that’s always full of hot water. A

nd the water you add while brewing a new butch goes to refill the reserve tank and not necessarily to brew your current butch.

So you can add an amount of water that won’t overfill your jug, but if you don’t change your brew volume to this amount, the water in your reserve will overfill your jug. 

Also, emptying your jug of your last batch is advisable before making a new batch.

This ensures you don’t exceed your maximum volume, and most importantly, it means you always have fresh coffee in the jog. 

Broken Spray Heads

Spray heads on Bunn coffee machines are fragile and easily break if not handled with care.

And broken or damaged spray heads change the spray pattern of water and spread it around and over to your counter.

So if you notice your spray head is damaged or not working correctly, make sure to fix or replace it before it starts to spray water unpleasantly. 

Bunn also recommends cleaning the spray heads on your coffee maker every few weeks.

This might seem complicated, but it’s actually easier than you think.

All you need is the deliming tool included with the brewer, toothpick, mild detergent, and the OEM also recommends using a soft cloth.

Next, unplug your coffee machine and let it cool.

After cooling, remove the brewing funnel and access the spray head. 

Then insert your deliming tool inside the spray head tube and slide it in and out a few times to remove the build-up of any gunk from your water sources.

Once this is done, turn your attention to the spray head.

And using a toothpick, unclog all its openings, and clean it with a cloth and mild detergent. 

Insert the spray head back into the coffee maker, fill it with cold water and cycle the water through the system to rinse it out.

Cleaning the spray head on your brewer will prolong the machine’s life; make sure your coffee tastes nice and help you avoid overflows. 

Resealing a Leaky Gasket

Sometimes, due to continued use, your Bunn coffee machine gives in and blows a gasket, or so to speak, and it starts to leak.

In such a situation, you may want to replace it or if you’re not ready to part ways with it just yet.

You can always reseal it using your DIY kit and get a few more miles out of your unit while saving a few bucks.

Due to the build quality of Bunn coffee machines, this usually means buying a few cheap replacement parts like new seals and a bit of elbow grease.

And with how fast the ice caps are melting, more people reusing and reducing their consumption is always a good thing for the environment. 

Using Hard Water

Hard water is notorious for clogging up water pipes and faucets in plumbing.

And when it comes to your Bunn coffee machine, it’s no different.

The accumulation of scale deposits in your unit’s plumbing can reduce water flow through the system and the resulting pressure build-up leads to overflows.

Regularly cleaning your coffee maker with vinegar is advised even if you don’t use hard water to make your brew.

This is because it helps to ensure your unit is clog-free and working optimally.

And also, coffee tastes better when it’s dirt-free.

Using filtered water with your Bunn coffee maker is preferred, but if you don’t have that option, don’t worry; cleaning it regularly also works.

And it’s something you should be doing regardless of if you use hard or filtered water.  

Broken pump valve

A pump valve regulates the amount of water flow to control the brew’s speed and potency.

A broken valve leads to the obstruction of the waterway, and with nowhere else to go, the water builds up in the brew funnel and eventually overflows.

To avoid this, it’s best to repair or replace broken pump valves.

The good thing with Bunn coffee machines is that they are easy to fix, and getting parts is also relatively easy. 

Also, check for mineral deposit build-up on the valve as that can also cause the malfunction.

Regularly cleaning the valve and the coffee machine will help avoid some of these issues.

Trust me, fixing an issue before it turns into a problem is always better. 

Removing the Carafe

Removing the carafe or jag when your Bunn coffee machine is brewing will

lead to coffee spillage all over your counter.

It’s essential to have it sitting in the proper position to catch the coffee when the brew is going.

And not having the carafe inserted or correctly positioned will lead to spillage and a mess in your kitchen.

Being attentive while making your brew can save you thirty minutes of cleaning.

FAQs About Buns Coffee Makers

Other than overflowing, people also have other questions relating to their Bunn coffee makers, and in this section, we’ll attempt to look at some of them.

Why the Brew Cycle Won’t Start

Nothing can be more disappointing than walking up to your coffee machine with a coffee mug in your hand, pressing the start on the machine, and then, nothing happens.

But worry not, we’ll have your mug full in no time.

Usually, this means you do not have enough water in your unit, and you should check the level.

If you find it’s too low, fill it up, and you’ll be on your way.

If the cycle still doesn’t start even after filling it up, this could be because the water is not yet up to temperature, and you should give it a few minutes to heat up. 

If the issue persists, check to see if the brew lockout is turned on and turn it off.

Next, check to see if your brewer is getting power by turning it on and off.

As you can see, the possibility of having to call in a technician goes higher and higher as you get down the list of possible faults with your Bunn coffee maker.

The other issues that could be plaguing your coffee machine could be software and hardware-related, such as a defective motherboard.

And if you do a visual and a basic inspection of your brewing unit, make adjustments to what you think might be wrong with it, and it still doesn’t resolve the issue.

Then, call for technical support and get a trained professional to help you out. 

Why Your Bunn Coffee Maker Makes an Unusual Sound

If you have been living with your Bunn coffee maker for a while and then it starts to make a stronger sound than usual.

One of the reasons could be because some of the plumbing lines are pressing against the countertop.

This might introduce strange vibrations, and releasing the plumbing lines from the surface they are in contact with will stop the vibrations and the sound. 

Another issue that can cause your Bunn coffee maker to make unusual sounds is loose inlet solenoid mounting screws.

Again, checking them and tightening them to spec should help remove the sounds.

Lime build-up in your water heater tank can also cause the unit to emit strange sounds.

If this is the case, clean and free the water tank from any lime to remedy the situation. 

One more thing you should check for strange noises is the pressure regulator on your unit.

The pressure should not exceed 90 PSI, and if it does, it could be the source of the strange sound and potentially be a hazard.

So replacing broken pressure regulators is always recommended. 

Why Your Bunn Coffee Maker is Brewing Weak Coffee

Waking up to a weak cup of coffee in the morning is annoying.

I don’t know about you, but I expect coffee to give me the caffeine boost I need to get my head working.

And a weak brew doesn’t cut it. 

If this is the case with your Bunn coffee maker, it could be because of using the wrong kind of coffee grinds.

If your coffee beans were ground too rough, then the coffee maker won’t be able to extract all of the caffeine and the taste of coffee from the ground.

As such, you should make sure the type of ground you’re using is neither too rough nor too finely ground. 

The other thing you should look out for when your brewer is brewing weak coffee is the settings on your unit.

For example, you might have it running at a high rate that does not allow for the proper infusion of the coffee ground and water.

And adjusting your brewing speed to one that brews a potency of your liking should be the first thing you do when you notice weak coffee. 

Defective or clogged spray heads can also affect the quality of brew your Bunn coffee maker produces.

A defective one can prevent your ground coffee in the filter funnel from getting wet.

Cleaning and replacing broken spray heads will keep your coffee machine functioning properly and help you avoid a weak brew.

Other than cleaning the spray head, the filter paper you are using could affect the output of your brewer.

And as such, you should only use Bunn’s filter paper with your Bunn coffee maker.

The filter paper plays an essential role in the brewing process as this is the part that allows caffeine and that coffee taste we love to filter out from the ground.

If the filter paper filters too fast, the brew could be weak, and if it filters too slow, you could have overflows and a cold brew.

A balance has to be struck between a filter paper that filters fast but not too fast for the brew to lack taste.

Filter papers that the OEM also recommends are good. 


Due to our love for coffee, we put up with a lot of issues that come with coffee machines.

And if you are one of the unlucky few, yours has more issues than the others.

But nonetheless, we press on.

And even with overflowing, damaged spray heads, clogged plumbing, and even units brewing weak coffee.

One thing is for sure; nothing will keep you away from your coffee.

And we are willing to clean out that clog, use our bare hands to fix it or even call a technician so that we can have a cup of coffee. 

With such devotion to coffee, companies like Bunn will continue to produce coffee makers that reduce the art of coffee making to perfection.

And as they continue to improve on their units, hopefully, they produce some with fewer issues.

Hopefully, if you are experiencing problems with your unit, content like this helps you find and fix your issue.

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