Thermal runaway and thermal dip

Owned by Chris Hilder
Last updated: Feb 22, 2024
2 min read

What does it mean when you see one of these warnings?

Thermal runaway
Press â–¶ to cool

or

Thermal dip
Press â–¶ to cool

This is an indication that the beans are not circulating properly and is known as Bean Lock. Due to lack of circulation hot air has become trapped in the bottom of the roast chamber, causing anomalies at the temperature probe. Roasting cannot proceed in a controlled way, so the roaster has stopped and is waiting for your intervention.

In the normal case simply press â–¶ to start cooling and wait for the cooling cycle to complete. In most cases the beans you were roasting will be ruined because the beans were not roasted evenly and the roast stopped early.

When the beans are cool and the roaster has stopped you need to make adjustments to your roasting practice so that the beans circulate adequately throughout the next roast cycle. This means using a smaller load or a higher fan speed. Check for initial circulation and adjust fan speed with Fan preview. For a more detailed explanation see Bean lock.

In vary rare cases the hot air trapped in the bottom of the roast chamber will heat some beans to the point where they begin to smoulder. In such a case you will see billows of dense black smoke, or in exceptionally rare cases you will see glowing beans or flames. If this is the case, turn the roaster off at the wall and treat as a chaff fire: either cover the top of the chaff collector with a pot lid, or remove the roaster to outdoors and wait for the fire to burn itself out. This is a very rare situation that most Kaffelogic users will never see. If it results in damage to the roaster contact customer support for assistance.

Is Bean Lock the only cause of these warnings?

No. There are other possible causes, but they are rare.

  1. If an element burns out during a roast you will get a thermal dip warning shortly after the element stops working. Test for this with a subsequent empty roast test: see Roaster not heating. The roaster will show a ‘Heat too slow’ warning during the empty roast test and your element needs to be replaced.

  2. If an element is malfunctioning (faulty thermal link, but element not burnt out) this can cause thermal dip warnings. This can be tested with a standard test roast:

    1. recalibrate bean circulation,

    2. use beans of average size and density such as most Colombian varieties,

    3. roast a 120g batch, and

    4. use the default profile (Kaffelogic Classic).

If thermal dip errors occur during a standard test roast, the element is most likely faulty and needs to be replaced.

  1. Some units manufactured in the first quarter of 2024 may show occasional spurious thermal dip warnings during normal roasts. If this happens, make sure your firmware is up to date (at least v7.11.8).

If you are in doubt about whether one of these faults might be present, contact customer support for assistance.

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