Breville “valv” error during descaling

I will only quickly go into this issue as I struck it the other day and it wasted some time, so this may help somebody. All the tips on the forums did not solve it but this method and explanation did.
On some models of the Breville, in my case the BES920, in order to complete the descale the boilers must be emptied. This is achieved by undoing the screws which drain both the steam and coffee boilers. This allows the boilers to be filled with descaling agent. However during the descaling procedure the machine sometimes fails to detect that the boiler has been emptied (usually steam boiler). It then throws up the “vale” error. You can not complete the descale, very annoying.

The Breville steam boilers have three probes, one is a ground, the other is a long low voltage one for detecting low water level, the third is a short of detecting upper water level. The upper and lower water probes have a voltage on them (usually 5v logic level), when water flows between the positive and the negative probes, a circuit is made. The micro can detect this so we have a switch that allows the micro to know the upper and lower water level status.

Sometimes when there is excess scale and crap or even descaling agent in the boiler, the low level probe will make a connection to the ground probe, even when the boiler is empty or excess scale may have stopped the boiler emptying completely. The forums tell you to flush the boiler repeatedly until it clears. In my case this did not work.

The solution I found was duing the descaling process, at the stage of draining the boilers, remove the connection to the low water level probe (open circuit). The machine then gets the message water level is low in the boiler and continues on with the descaling process, instead of hanging. By the way try cleaning the probes as well before doing this live, you may also need to remove the probes to ascertain which is the low water level probe. Now a warning the machine is hot with 230V to the elements and they (probes) are located very near to the elements on the coffee boiler. You will get a shock if you touch the element and to prove it I did it, I describe the experience as “shocking”. Be very careful. I wear rubber shoes and don’t seem to ever die.