Breville Bes-920 no Crema and bad tasting coffee issue fixed

Just a quick service note on a Breville Bes920 that came in recently. The pressure gauge was not working at all and the customer was complaining that the coffee no longer had crema and did not taste good.
It turned out to be multiple factors contributing to the issue so I thought it worth going over them, these will be of interest to Breville owners.


Poor quality coffee from a Breville Coffee Machine

I happened to have an identical Breville BES920 in the shop and it made great coffee. It had the Breville buzzing valve syndrome which I will blog about later. Anyway I conducted a flow test, as this unit has a nice timer function, I timed how long it took to fill a shot glass. This included the infusion time that is programmable. The good unit filled the glass in 17 seconds, the unit making the poor quality coffee took 30 seconds. So clearly a flow issue. The temperature of the water was perfect. This measurement was achieved with an empty portafilter obviously.

breville pressure gauge

replacing a Beville pressure gauge

I firstly checked that the pressure gauge was receiving water. It was, so I removed it and tested it, it was faulty. A common problem on these machines. I replaced it (not expensive from Breville) and the new one was registering very low pressure with the blind filter in place. Somethings up?
Because the pump sounded loud I checked the supply line and cleaned the flow meter. Water supply was a little slow, possibly some crap in the line which was removed after my inspection. Note there are restricters in the flow meters which accumulate crap. Flow meters can be cleaned by removing the top and flushing them out. Don’t just buy a new one, unless you want to buy it from me.

As pumps are expensive and customers do not like paying for new ones, I left this to last, in case something obvious and cheaper was the cause. I checked the valves and water lines. The water line did have a leak on the hot o-rings. Again this is common in the Breville, so I replaced all the o-rings in the water line. Cleaned the shower screen and other obvious things.
Breville machines tend to readily accumulate scale in boilers and this can inhibit flow rates. I inject such boilers and blocks with acid and gave them a descale like they have never had before, this flushes a lot of scale out. Note as the steam boiler distills water, scale accumulates in the steam boiler on the hot surfaces. This scale can break off and travel into valves and jets, blocking them. and the coffee line goes through the steam boiler and collects scale, so scale is a probable cause of low flow rate in these and any coffee machine. It is very common in the Breville machines for the jet at the bottom of the 3 way valve to scale up. See picture below. The while seal is meant to have a significantly larger orifice than the pin hole seen here.

breville valve blocked

Next I checked the pump bypass. These appear to be adjustable, although my experimentation revealed no obvious change in pump pressure with adjustment. These bypasses I know from experience are a cause of low pressure. They fail and bypass too much of the water flow. This one was ok, I know as I tried a new one, same pressure. Note if you have a block in the hydraulic line you will see a lot of water going down the bypass as its venting as the pressure is high. Like all coffee machines with the blind filter in place the pressure gauge should read 9 bar.

920 pump bypass

pump bypass bes920

So finally the pump, an Ulka. It looked fine but after replacing it, the pressure was up at 11 bar with the blind filter in place. So in summary, a blocked pump was the main culprit, but scale, a leak and blockages in the flow meter contributed.

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