Troubleshooting The Dual Boiler BES920 After a Failed Descale

In this post, we will cover some steps you can take if your machine is no longer heating up following a descale.

If you own a Breville BES920, and specifically one that has the older version 2 steam boiler, descaling the machine comes with significant risks. This article will outline the dangers involved, explain the underlying issues, and provide guidance on how to mitigate the risks.

Why the BES920’s Sensors Are Problematic

The Breville BES920, like the other dual boiler models, relies on water level sensors to determine when to activate the pump or heat. However, versions of the BES920 manufactured before mid-2022 with other older water level sensors are highly susceptible to failure, particularly during the descaling process. Here’s why this is a concern:

• Descale Solution Contamination: During the descaling process, the descale solution can inadvertently come into contact with the probes. This contamination mimics the presence of water, leading the machine to misinterpret the water levels in the boiler.

The Consequences of Probe Contamination

When descale solution residue affects the probes, one of two scenarios can occur:

• Red Probe Contamination (Pump Control): The red probe governs the water pump. If it becomes contaminated, the machine will falsely register the boiler as full. The result? The boiler won’t heat up. While this issue is inconvenient, it’s fixable—though you may need to remove the top cover to clean the probe thoroughly.
• Blue Probe Contamination (Heat Control): The blue probe is responsible for controlling the heating element, and contamination here can lead to catastrophic consequences. If the machine believes the boiler is full due to false readings, it will activate the heating element before the boiler is actually filled. This causes rapid overheating, which can:

1. 1. Blow the thermal fuse.
   2. Permanently damage the heating element.
   3. Require a complete boiler replacement, costing upwards of $600.

How to Protect Your Machine

To reduce the risks associated with descaling your BES920, consider these precautions:

• Use a Professional Descaling Service: If you’re uncertain about handling the process yourself, consult a professional technician who can descale the machine safely.
• Avoid Overdosing: Ensure that you only use the recommended (or less) amount of descale solution to minimize the risk.
• Replace the Probes: If possible, consider replacing the probes with new ones. Brand new probes still have their protective coating and are not vulnerable to this.
• Follow the instruction outlined in this video to help you assess the condition of your machine before carrying a descale: Will Your Breville Survive a Descale? - Part1

Do I have the older, version machine?

From what I've seen, Breville changed to the new version of steam boiler around the middle of 2022, but this is not a guarantee as some machines appear to have later dates on them - maybe relating to certain colours or countries.

Here is how to find out which version you have:

1. Remove the top lid. The older version has water level probes held in with clips. The newer ones have a compression fitting nut on them. The red probe is also in the middle and on the right for the older ones.

Conclusion

Owners of pre-2023 models need to exercise caution when descaling as contamination can lead to costly repairs. 

To further assist you, I’ve created a flowchart that allows you to troubleshoot common issues related to descaling and water level sensors (click to open in new tab):