Descaling is the single most consequential maintenance task for the Breville BES870XL Barista Express. The machine heats water to 200°F (93°C) and forces it through a thermocoil and group head at 9 bars of pressure on every single shot, conditions that accelerate mineral precipitation from dissolved calcium and magnesium in tap water far faster than any low-temperature appliance. A BES870XL that is never descaled accumulates calcium carbonate scale on the thermocoil’s interior walls, inside the solenoid valve’s small orifices, along the flow path between the pump and group head, and at the shower screen. Each layer of scale reduces flow, increases the pump’s working load, reduces temperature accuracy at the puck, and eventually contributes to the cascade of failure modes low pressure, uneven extraction, overheating that bring machines in for repair.
Done correctly and on schedule, descaling prevents all of this. This guide covers the complete procedure with the technical depth the BES870XL’s specific architecture requires.
WHY THE BES870XL SCALES FASTER THAN MOST COFFEE APPLIANCES
The BES870XL’s thermocoil design creates specific conditions for rapid scale formation. Unlike a traditional boiler that holds water at temperature for extended periods, the thermocoil is a thin-walled coiled tube through which water passes once heated from cold to extraction temperature in a single continuous passage. The abrupt temperature transition from cold inlet to 200°F output happens across a short physical distance, creating a zone of maximum thermal stress on dissolved minerals precisely where the tube walls are thinnest and surface area is most concentrated.
Calcium carbonate’s solubility decreases with increasing temperature, the opposite of most dissolved substances. This means the hotter the water, the faster minerals precipitate out of solution and onto the nearest solid surface, which in the thermocoil is the tube’s inner wall. Each brew cycle deposits a microscopic layer. Over hundreds of brew cycles without descaling, this layer becomes thick enough to measurably reduce the thermocoil’s internal bore, increasing flow resistance and reducing the machine’s ability to maintain consistent extraction temperature.
The practical consequence
A heavily scaled BES870XL produces shots that taste sour or weak (temperature too low from restricted thermocoil flow), runs longer than usual to fill the portafilter, shows inconsistent pressure gauge readings, and eventually stops pumping water altogether; the scale has occluded the flow path to the point where the pump cannot overcome the restriction.
HOW OFTEN TO DESCALE THE BES870XL
Breville’s general recommendation is every 60–90 days of regular use. This interval is based on moderate tap water hardness. The correct interval for your specific installation depends on water hardness:
Water hardness and descaling interval:
- Soft water (0-75 ppm TDS): every 4-6 months
- Moderate water (75-150 ppm TDS): every 2-3 months
- Hard water (150-250 ppm TDS): every 6-8 weeks
- Very hard water (above 250 ppm TDS): every 4-5 weeks
Using a water hardness test strip (available from home brewing and aquarium suppliers) on your tap water gives the specific TDS reading and the appropriate interval.
Observable signs that descaling is overdue (do not wait for these; descale on schedule):
- Shots pulling longer than the standard 25–30 seconds for the same dose and grind
- Lower reading on the pressure gauge than the usual 9-bar extraction range
- Machine taking noticeably longer to heat up to ready state
- Steam wand producing reduced steam volume or pressure
- Any sign of low water pressure in the flow pathway
CHOOSING THE CORRECT DESCALING SOLUTION
The BES870XL is a high-pressure espresso machine; the descaling agent must be compatible with its internal components: stainless steel thermocoil, brass solenoid valve, silicone hoses, plastic water path components, and rubber O-rings. Not all descalers are safe for all of these materials.
Compatible descaling agents
Breville Descaler (Part #BES006)
Breville’s purpose-formulated descaling tablet or liquid solution. Designed specifically for Breville espresso machines and guaranteed compatible with all internal materials. The simplest choice for BES870XL owners.
Citric acid solution (10-15% concentration)
Citric acid is food-safe, highly effective at dissolving calcium carbonate scale, and compatible with the BES870XL’s internal materials. Mix 15–20 grams of citric acid powder in 1 liter of water. Citric acid is the active ingredient in most commercial coffee machine descalers.
Commercially available espresso machine descalers
Dezcal (Urnex), Cafiza descaling liquid, and equivalent products formulated for espresso machines are compatible. Confirm the product is specifically rated for espresso machines with thermocoil or heat exchanger designs, not coffee maker descalers formulated for drip machines.
Incompatible or not recommended
White vinegar
Widely used in kitchen appliances but not recommended for the BES870XL. Vinegar’s acetic acid is a weaker descaler than citric acid, requires more volume to be effective, can leave residual taste in the machine that lingers through multiple flush cycles, and the acetic acid may degrade certain rubber seals over time with repeated use. The risk-benefit ratio does not favor vinegar when purpose-formulated descalers are available.
Bleach or household cleaners: Incompatible with all internal materials. Never use.
MATERIALS REQUIRED BEFORE STARTING
- Descaling solution (Breville Descaler or citric acid solution prepared at the correct concentration)
- Fresh water for preparation and rinsing
- A large bowl or container (minimum 2-liter capacity) to collect the descaling solution as it exits the machine
- A clean damp cloth for wiping
- Approximately 45–60 minutes of uninterrupted time
THE BREVILLE BES870XL DESCALING PROCEDURE: STEP BY STEP
The BES870XL does not have a dedicated automatic descaling mode accessible through a button sequence in the same way some Breville models do. The descaling procedure for the BES870XL is a manual process using the machine’s existing brew and steam functions to circulate the descaling solution through the internal flow path.
Preparation phase:
Step 1 – Empty the water tank completely. Remove the tank from the machine.
Step 2 – Remove the water filter if installed. The Breville water filter (charcoal filter in the tank) must be removed before descaling; the descaling solution will saturate and damage the filter media. Set the filter aside and discard it after descaling (replace with a new filter after the descaling process is complete).
Step 3 – Remove the portafilter and the single-wall basket insert. The portafilter should not contain a filter basket during descaling; you want the descaling solution to flow freely through the group head without restriction.
Step 4 – Prepare the descaling solution. If using Breville Descaler tablets, dissolve one tablet in 1 liter of lukewarm water per the product instructions. If using citric acid, dissolve 15–20 grams in 1 liter of water. Fill the water tank with the prepared descaling solution.
Step 5 – Place the large collection container under the group head. The container needs to hold the full volume of descaling solution that will pass through the machine.
Descaling flush phase
Step 1 – Turn on the machine and allow it to reach operating temperature (the ready indicator will illuminate or stop flashing, typically 30-45 seconds).
Step 2 – Begin the descaling flush by activating the 2-cup brew button (or the largest volume brew selection on the BES870XL). Allow the descaling solution to flow from the group head into the collection bowl. The first pass of solution begins working on scale in the thermocoil, solenoid valve, and group head flow path immediately.
Step 3 – When the pump stops (the tank is approaching empty or the machine pauses the cycle), allow the machine to rest for 5 minutes with the descaling solution in the internal passages. This dwell time allows the citric or other acid to contact and begin dissolving scale deposits that the flowing solution may have only partially reached.
Step 4 – Activate another brew cycle. The machine will flush remaining solution from the water tank. Allow it to complete.
Step 5 – Purge the steam wand. Fill the tank with a small amount of the same descaling solution (approximately 200–300mL remaining if available). Place a collection cloth or small bowl under the steam wand. Open the steam valve and allow the descaling solution to pass through the steam boiler and steam wand. This descales the steam pathway simultaneously with the brew pathway; neglecting the steam wand allows scale to accumulate in the steam boiler even after the brew path is descaled. Close the steam valve after purging.
THE RINSE CYCLE: THE MOST CRITICAL STEP
Inadequate rinsing after descaling leaves descaling agent residue in the machine’s internal passages. This residue produces bitter, chemical-tasting espresso for days after descaling and, in the case of citric acid, can continue to attack internal components at low concentration. The rinse cycle is not optional; it is as important as the descaling flush itself.
Rinse cycle procedure:
Step 1 – Empty the collection bowl and discard the used descaling solution. Rinse the collection bowl with clean water.
Step 2 – Empty any remaining descaling solution from the water tank. Rinse the tank thoroughly with clean water. Refill with fresh, clean water to the maximum level.
Step 3 – Position the collection bowl back under the group head. Activate the brew cycle and run the entire tank of clean water through the group head. This first rinse cycle flushes the majority of descaling solution from the brew pathway.
Step 4 – Refill the tank with fresh clean water. Run a second complete rinse cycle through the group head. Two full rinse cycles are the minimum; three is recommended for machines descaled with citric acid solution (citric acid has a subtle flavor even at very low concentration that requires thorough flushing).
Step 5 – Purge the steam wand again with clean water from the final rinse fill. Open the steam valve briefly to flush the steam path clean.
Step 6 – Reinstall the water filter (new filter if the old one was exposed to descaling solution).
POST-DESCALING VERIFICATION
After completing the rinse cycles, run a shot of espresso (with a properly dosed portafilter and fresh coffee) to verify machine performance. A successfully descaled BES870XL should show:
- Shot pulls in the standard 25-30 second window for the same dose and grind setting that was used before descaling
- Pressure gauge reading in the 8-10 bar extraction range
- Consistent flow from the group head (no spurting or channeling caused by restricted orifices)
- No unusual taste in the espresso (chemical, sour, or metallic notes indicate insufficient rinsing; run additional flush cycles)
- Normal steam wand pressure and steam volume
WHAT DESCALING CANNOT FIX: UNDERSTANDING ITS LIMITS
Descaling dissolves and flushes mineral scale from the machine’s water flow path. It does not address:
- Coffee oil residue buildup in the group head, shower screen, or portafilter; this requires regular backflushing with a blind basket and espresso machine cleaner (Cafiza or equivalent)
- Mechanical wear in the pump or solenoid valve: scale removal may reveal that the pump’s pressure output is reduced from age regardless of scale
- A thermocoil that has been damaged by severe scale accumulation: if the thermocoil’s tube walls have been compromised by scale that has been in place for years, descaling removes the scale but cannot repair the damaged metal
For machines that have never been descaled and show severe symptoms no water flow, very low pressure, complete failure to pump descaling is the appropriate first intervention, but the underlying pump or thermocoil condition may require component-level evaluation after the descaling is complete.
