i just got a used magnifica s and the coffee tastes terrible, like burnt plastic or chemicals.

Diagnosis

The "burnt plastic" or chemical taste in a used De'Longhi Magnifica S is typically caused by a combination of stale water stagnation and residual cleaning agents. Because these machines use a network of silicone tubing and a stainless steel boiler, water that sits idle for weeks or months during a sale develops a biofilm or absorbs the scent of the surrounding plastic housing. If the previous owner used a heavy-duty descaler or a chemical milk-circuit cleaner without a thorough rinse, these alkaline residues cling to the internal walls of the thermoblock. Furthermore, the Magnifica S features a removable infusion unit (the "heart" of the machine). If this was not cleaned before the machine was stored, old coffee oils have oxidized and gone rancid. When hot water hits these oxidized oils, it creates a pungent, acrid flavor that mimics burnt plastic or chemicals. You can confirm this by running a "blank" shot of hot water; if the water itself smells like chemicals, it is a plumbing issue. If the water is fine but the coffee tastes foul, the residue is trapped in the brew group or the bean hopper.

How to Fix It

You need to perform a deep systemic purge. Do not use expensive coffee beans for this process; use the cheapest roast available or run blank cycles.

1. The Water System Flush: Fill the water tank to the MAX line with filtered, room-temperature water. Place a large 1-liter pitcher under the coffee spouts. Using the brew dial, select a "medium" coffee setting and run 5 full cycles without adding beans. Then, turn the steam dial to the "ON" position and dispense hot water through the steam wand for 60 seconds to clear the boiler's secondary lines.
2. The Infusion Unit Deep Clean: Open the side service door (behind the water tank). Press the two red buttons to release the brew group (infusion unit). Remove it entirely. Do not use soap; rinse it under lukewarm running water until all brown sludge is gone. Use a soft brush to clear the piston area. Let it air dry for 30 minutes before sliding it back in and locking it with a firm click.
3. The Hopper Purge: Use a vacuum cleaner to suck out any old beans or dust from the bean hopper. Wipe the interior of the hopper with a damp cloth and dry it completely. If the previous owner used flavored beans, the oils will have seeped into the upper grinder burrs; run a small handful of "cleaning pellets" or very light roast beans through the grinder to absorb the old oils.
4. The Final Calibration: Run one final "Long" coffee cycle. Discard this cup. The second cup should now taste neutral.

If That Didn't Work

• Perform a Full Descaling Cycle: If the chemical taste persists, the previous owner may have left descaling solution in the boiler. Use a De'Longhi EcoDecalk solution (100ml). Follow the descaling prompt on the machine, letting the solution sit in the boiler for 15 minutes between discharges to break down the chemical buildup.
• Replace the Water Filter: If your model has the internal water filter (the small plastic cartridge at the bottom of the tank), remove it immediately. Old filters become breeding grounds for bacteria and can impart a metallic or plastic taste to the water. Run the machine without the filter for three cycles to see if the taste improves.
• Clean the Coffee Spouts: The plastic nozzles where the coffee exits can trap old oils. Gently pull the spout assembly forward and wipe the interior of the nozzles with a cotton swab dipped in white vinegar.
• Check the Gasket: Inspect the large rubber O-ring on the brew group. If it looks cracked or "melted," it may be leaching a rubbery taste into the coffee. Apply a tiny amount of food-grade silicone grease to the seal to refresh it.

Heads Up

• Avoid Dishwashers: Never put the brew group or the drip tray in the dishwasher. The high heat warps the plastic and strips the lubricants, which will lead to a grinding noise and eventual mechanical failure.
• Water Quality: Using distilled water can actually trigger "low water" sensors and cause the pump to cavitate. Use filtered tap water for the best balance of taste and machine longevity.
• Weekly Maintenance: To prevent the return of this taste, remove the brew group every Sunday and rinse it under the tap. This prevents the buildup of rancid oils that cause that "burnt" flavor.
• Bean Storage: Store your beans in an airtight container, not the hopper, to prevent the oils from oxidizing and sticking to the grinder burrs.