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To descale a BUNN home brewer: unplug it, run a citric acid descaling solution through the spray head path, clean or replace the spray head and clear its feed tube (BUNN sells a deliming spring tool for exactly this), then flush the machine with several full carafes of fresh water before brewing again. BUNN's home design keeps a tank of water hot at all times, which is why it brews so fast and also why it scales faster than a cold-tank drip machine. Match the tank-flush details to your specific model's manual; the chemistry and the flush pattern below are universal. On typical tap water, deep-clean every 2 to 3 months.
Why BUNNs scale faster than other drip machines
Most drip machines heat water only during a brew. A BUNN home brewer holds a full internal tank at temperature around the clock, and hot water drops minerals out of solution faster than cold water does. The payoff is a brew in about the time it takes to pour; the cost is that calcium carbonate builds on the tank walls and in the spray head continuously, not just while brewing. The spray head's small holes are the first thing to clog, which is why BUNN's own maintenance kit is a spring you snake through the spray tube rather than just a bottle of acid.
Symptoms and what they mean
| Symptom | Likely scale problem |
|---|---|
| Brew suddenly slower than its usual sprint | Spray head holes or feed tube narrowing with deposits |
| Water dribbles instead of spraying over the grounds | Clogged spray head; weak, uneven extraction follows |
| Short pots from a full reservoir pour | Scale displacing volume and restricting the tank outlet |
| Gurgling, popping, louder operation | Water fighting past deposits on the hot tank walls |
| Lukewarm coffee | Scale insulating the heater; also see BUNN not heating |
The universal deep clean
Unplug the machine and let it cool. Remove the spray head and soak it in citric acid descaling solution; run the deliming spring or a soft probe through the spray tube until it moves freely. Then run descaling solution through the brew path the way your manual directs for your model, let it work 20 to 30 minutes, and flush with fresh water until the output is clear and has no sour smell, usually 3 or more full carafes. Citric acid is the right chemistry because it turns limescale into soluble salts that rinse away (descaling agent chemistry); vinegar also works on scale but lingers in a machine that stores hot water, so every pot for days tastes like it.
Related reading
FAQ
How do I descale a BUNN coffee maker? Unplug it, soak the spray head in citric descaling solution, clear the spray tube with a deliming spring, run solution through the brew path per your model's manual, then flush with 3 or more carafes of fresh water.
Why does a BUNN need descaling more often than other brewers? It keeps an internal tank hot at all times, and hot water deposits minerals faster. Scale builds around the clock, not just during brews.
Can I run vinegar through a BUNN? Citric acid descaler is the better tool. Vinegar's smell lingers badly in a machine that stores hot water, and it is harsher on seals over repeated cycles.
Descaler chemistry per the descaling agent reference above; match tank-flush steps to your BUNN model's manual.
Never miss a cycle: the free one-page Machine Maintenance Calendar (PDF) puts every daily, monthly, quarterly, and yearly task for espresso machines, drip, Keurig, and moka pots on a card you can tape inside a cabinet.
Improving your brew? Browse our free coffee tools, print the brew ratio card, and try our method: the descending pour.