You are probably aware, that the temperature displayed on the front of your 900 series coffee machine, is an average of the three heating elements(*1), Coffee boiler, steam boiler and the block element. So when a machine fails to reach the operating temperature, usually 93°, it is often because one of these elements has failed for some reason or other.

This was another of the “other reasons”, yes another not so obvious solution hence why I am blogging about it.

In the case of this machine, we had already replaced the steam boiler, and reattached the thermostat. The latter had a corroded metal band that holds it to the steam boiler and was flapping around in the wind, so we naturally assumed this was the cause of all our weird issues. Well the ones related to the coffee machine. The machine had been failing to heat and was hanging around 60 to 83° degrees, on the odd occasion it would reach temperature (93) but not for long. And on other occasions according to the customer it would go over temp. So it was a weird one, and an unattached thermostat made perfect sense. It didn’t actually but I was in a hurry for lunch. Anyway to our dismay, after removing the steam boiler and reattaching the thermostat , the bloody machine still did not reach temperature. We got what we deserved for not thinking hard enough about the issue. I actually thought, buggar we should have replaced the thermostat not just reattached it. If you have ever removed the boiler from one of these Breville machine’s and put it back, you will know, its not a job you want to do twice.

Here were the facts;

  1. The steam boiler appeared cold (in my defence, this had not been the case before reattaching the thermostat). The steam boiler had heated up, but it was now stone cold.
  2. I got 47 ohms back from the steam boiler, indicating the element, the fuse and probably the thermostat were all okay.
  3. The old light bulb trick, confirmed no voltage was being switched to the steam boiler element.

I had no idea what was going on. So I reset the error codes and and ran the machine up again and again. It hung at about 60 – 70° every time. I then looked up the error codes again and I had seven errors on 21, which according to the service notes is “Steam high water probe short but low probe open error”, so the machine is registering the water being high, but also the water being low, there’s no voltage coming from the low probe.

Error 21 – seven times – trouble with the low water probe (blue wire, middle probe)

Normally I would just replace the low probe, but it was obvious the connectors were very corroded and anyway probs were in short supply. Inspection of the probe connector revealed a high resistance connection and when I shorted the wire to the probe, my lightbulb lit up, indicating I had voltage to the element. And indeed I did, as the machine booted up and reached normal operating temperature.

Corroded probe connector
Now a fuzzy close up
Voltage to the element, thus light from the bulb, note the clamp holding the blue wire to the low water probe, proving the open low water probe connection was the cause of the power failure to the steam boiler.

In conclusion, I think we had two issues here. The thermostat flopping around in the wind and the error 21. Why the steam boiler sometimes heated, I’m not sure, probably an intermittent connection to the probe. The thermostat not being flush with the steam boiler also contributed to some of the weird temperatures the customer had described.

A happy machine.


  • To the fab people at Outwest… I had read your troubleshooting guides for the BES980 to determine the ‘ol steam-boiler-isn’t-hot fault after attempting the descale. First time this happened after much non-invasive correction attempts we gave up and called Breville who took a lengthy month to rectify (air bubble thankfully nothing more).

    Second time this happened – much cursing later – didn’t want to wait for Breville so came back to your amazingly helpful site, went thru diagnosing and changing the thermal fuse (which was blown), the traics (prob was ok) … still the damn thing was not heating. frustrating! So, went thru your articles very very carefully and just found this last article which I missed until now! Amazing, we have coffee again. Till next time 😉 Wanted to wish you a huge thanks!

    Ps – could you do an article about the firmware / various version differences and is it worth updating it?

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