Descaling removes mineral buildup that slows water flow and weakens your brew

Over time, minerals from tap water — mainly calcium and magnesium — collect inside your BUNN coffee maker's heating tank and tubes. This buildup, called scale, narrows the passages water travels through, so your machine brews slower and hotter water sits longer on the grounds, making coffee taste bitter or weak. Descaling dissolves that mineral layer and restores normal water flow and temperature.

Most BUNN models need descaling every 3 to 6 months, depending on your water hardness. If you have very hard water (high mineral content), descale every 3 months. Softer water means you can wait 6 months. The process takes about 15 minutes and uses a commercial descaling solution — white vinegar works in a pinch, but BUNN recommends their own descaling liquid or a citric acid solution because vinegar can leave a smell.

Key Takeaways

  • Scale buildup slows water flow and makes coffee taste bitter; descaling every 3 to 6 months prevents this.
  • BUNN descaling solution or citric acid solution works best; white vinegar is a backup but may leave an odor.
  • The process involves filling the water tank with descaling solution, running it through the brewer, and then flushing with fresh water multiple times.
  • Never use vinegar in BUNN machines designed for their own descaling liquid, as it can damage internal seals over time.
  • If water barely drips or the machine won't heat, descaling may restore function, but severe blockage sometimes requires professional service.

What you need before you start

Gather these items: a BUNN-approved descaling solution (BUNN Cleaner or a citric acid-based descaler), a large empty pitcher or sink basin, and fresh water for rinsing. Check your BUNN model's manual to confirm which descaler it accepts — some older or commercial models have different requirements. If you cannot find your manual, BUNN's website has downloadable PDFs by model number.

Make sure your coffee maker is unplugged and has cooled for at least 30 minutes. Empty the water tank completely and remove any paper filters or grounds from the brew basket. If your BUNN has a removable water tank, take it out; if it's built-in, you'll fill it in place.

Running the descaling solution through your BUNN

Fill the water tank with the descaling solution according to the product's instructions — usually one packet or bottle mixed with water to a specific level marked on the tank. If you're using a commercial BUNN descaler, follow the ratio on the package; if using citric acid, dissolve about 1 to 2 tablespoons per full tank of water.

Place your empty pitcher under the brew funnel to catch the liquid. Plug in the machine and let it heat for 5 to 10 minutes until you hear the pump running or see water beginning to flow. Once water starts dripping, let it run continuously until the tank is empty — this usually takes 5 to 8 minutes. Do not brew a pot; you're flushing the solution through the entire system, including the heating tank and internal lines.

After the tank empties, unplug the machine and let it sit for 15 to 20 minutes. This gives the descaling solution time to break down stubborn mineral deposits inside the heating tank where you cannot see them.

Rinsing out the descaler completely

Refill the water tank with fresh, cold tap water — no descaler this time. Plug the machine back in and run the full tank through the brew funnel into your pitcher, just as you did with the descaling solution. This first rinse removes most of the descaler.

Repeat the rinse cycle two more times with fresh water each time. After three complete rinses, your BUNN should no longer smell like descaler or vinegar. If you used vinegar and still smell it after three rinses, run one or two additional cycles — vinegar odor can linger longer than commercial descalers.

Once rinsing is complete, empty the pitcher, replace any water filter if your model has one, and refill the tank with fresh water. Run one final brew cycle into a cup to confirm the water tastes normal and the machine heats properly. Discard this test cup — it may still contain trace descaler.

Signs your BUNN needs descaling sooner

If water drips very slowly from the brew funnel, or if the machine takes much longer than usual to brew a full pot, scale is probably blocking the heating tank or spray head. Descaling should restore normal speed. If the water comes out noticeably hotter than before, that's also a sign of scale buildup — minerals insulate the heating element, so it overheats to compensate.

Some BUNN models have a descale indicator light that turns on when minerals reach a certain level. If yours has one and it's lit, descale when ready — waiting longer can damage the heating element or pump. If your machine stops heating water altogether or produces only a trickle, descaling may fix it, but if water still won't flow after a full descale cycle, the pump or heating tank may need professional repair.

Choosing between BUNN descaler and alternatives

BUNN's official descaling solution is formulated specifically for their machines and won't leave residue or odor. It costs roughly $5 to $8 per packet and works quickly. Citric acid solution (sold as a descaler at most grocery stores or online) is cheaper and works well, though it may take slightly longer to dissolve heavy scale.

White vinegar is a last-resort option if you have nothing else on hand — it does descale, but BUNN warns that repeated vinegar use can corrode internal seals and valves over time. If you use vinegar, limit it to once or twice a year and rinse extra thoroughly. Never mix vinegar with commercial descalers, and never use descaling powder meant for kettles or other appliances in your BUNN, as the particle size can clog the spray head.

Preventing heavy scale buildup between descales

If your tap water is very hard, consider using filtered or distilled water in your BUNN. Filtered water has fewer minerals, so scale builds up more slowly. You don't need to use it for every pot — even filling the tank with filtered water half the time cuts mineral buildup roughly in half. This extends the time between descales and keeps your coffee tasting fresher.

Drain the water tank if you won't use your BUNN for more than a week. Stagnant water in the tank can leave mineral deposits even when the machine isn't running. A quick empty and refill before your next brew prevents this.

Frequently Asked Questions

Can I use white vinegar instead of BUNN descaler?

Vinegar works in an emergency, but BUNN advises against regular use because it can damage internal seals over time. If you do use it, mix one part white vinegar to one part water, run it through once, then rinse at least four times with fresh water to remove the smell.

How often should I descale if I use filtered water?

Filtered water slows mineral buildup, so you may only need to descale every 6 to 9 months instead of every 3 to 6. Watch for slower brewing or hotter-than-normal water as signs to descale sooner, regardless of the calendar.

What if my BUNN still brews slowly after descaling?

Run the descale cycle one more time — heavy scale sometimes needs two treatments. If it's still slow after a second descale, the spray head or pump may be partially blocked and could need professional cleaning or replacement.

Is it safe to drink water that ran through during descaling?

No. Always discard the first pot or two after descaling. Even after rinsing, trace descaler can remain in the lines. Run at least one full tank of fresh water through before brewing coffee you plan to drink.

Do I need to descale if I only use my BUNN occasionally?

Yes, but less often. Even if you brew only once a week, minerals still accumulate in the heating tank. Descale every 6 to 9 months depending on your water hardness, or whenever you notice slower brewing or temperature changes.