How to Fix: Espresso Machine Low Flow Rate

Recently, I encountered a situation where my espresso machine had a significantly reduced flow rate. The water trickled slowly through the group head, rendering it impossible to produce a palatable espresso shot. It took some time to diagnose the problem, but fortunately, I managed to rectify it without the need for professional assistance from an espresso machine engineer.

I’ve posted my advice and fixes below which can hopefully help if you are experiencing the same issue with your machine. The machine with the issue was the Gaggia Classic Pro, but I these solutions could work on many other models too such as the Breville Bambino, Rancilio Silvia, Rocket Apartmento, etc.

What is a low flow rate?

A flow rate in an espresso machine refers to the rate at which water passes through the coffee grounds during the extraction process. It's typically measured in milliliters per second (ml/s) or grams per second (g/s).

In terms of actual values, a low flow rate can vary depending on the specific espresso machine and its settings, but generally, it would be significantly slower than the desired flow rate for optimal espresso extraction. For example, if the ideal flow rate for your espresso machine is around 1.5-2.5 ml/s, a low flow rate might be anything significantly below this range, such as less than 1 ml/s.

A low flow rate can result in under-extracted espresso, with a thin and weak flavour profile, as well as potential channelling (uneven water distribution through the coffee puck) which can further degrade the quality of the espresso shot.

7 Reasons for a Low Flow Rate

1. Grind Size

This may feel a tad obvious, but it’s still worth checking. If the coffee beans are ground too finely, it can restrict the flow of water through the coffee puck, resulting in a slow extraction. Adjust the grind size coarser to allow for better water flow.

3. Limescale Build Up

If you live in a hard water area, you may have a build up of limescale in your machine which can cause certain elements to get clogged with scale. Make sure you descale your machine on a regular basis with a descaler recommended by your machine manufacturer. For the Gaggia Classic I use the Gaggia Descaling Solution.

4. Coffee Dose

Using too much coffee in the portafilter can also lead to a low flow rate. Stick to the recommended dose for your espresso machine and adjust as needed.

5. Machine Pressure

Check the pressure gauge on your espresso machine to ensure it's operating within the appropriate range. Low pressure can result in slow extraction.

6. Water Temperature

If the water temperature is too low, it can affect the extraction process, leading to a slow flow rate. Make sure your espresso machine is heating the water to the correct temperature.

7. Faulty Equipment

In some cases, a low flow rate may indicate a mechanical issue with the espresso machine, such as a malfunctioning pump or valve. If none of the above solutions resolve the issue, it may be necessary to have the machine inspected or serviced by a professional technician.

How Did I Fix My Gaggia Classic Pro Low Flow Rate?

It turned out that my Gaggia Classic Pro had a low flow rate due to scale being stuck in the solenoid valve creating a blockage. So to fix it, I did the following:

• Backflush Machine

Backflushing is a way to remove coffee oils, residue, and other impurities that can build up in the machine's group head, portafilter, and dispersion screen over time. Insert a blind filter/blanking plate in your portafilter, insert some cleaning solution (I used Puly Caff), lock the portafilter and run water through the group head, repeat and rinse. In some cases, the low flow rate may be so poor that it can’t produce enough water for a backflush, if so, skip this step.

• Removed Solenoid Valve for Descale

I took my machine apart and soaked the solenoid valve in descale solution, following the instructions from this video from Whole Latte Love on YouTube. This helps to remove any scale that may be causing a blockage.

• Quickly Switch the Water Flow

On the Gaggia Classic Pro, I turned the steam valve on, pressed the espresso button and then turned the steam button on and off quickly for around 20 seconds. This quickly alternated the flow between the group head and the steam output which managed to dislodge the bit of scale blocking the solenoid valve. This was particularly useful because even after descaling, this stubborn piece of scale wouldn’t budge. Using this technique helped to regain a normal water flow to the group head.

In essence, if you notice a low water flow rate in your Gaggia Classic Pro or a similar machine, there are various solutions to explore. Should the problem persist, I suggest reaching out to the manufacturer for guidance. While these solutions proved effective for my machine, yours may vary, hence it's prudent to consult the manufacturer's instructions and exercise caution, especially when disassembling your espresso machine.