What coffee machine should I buy? Boiler vs Thermoblock

What Coffee Machine Should I Buy? Boiler vs. Thermoblock Explained

The big difference: boiler versus thermoblock 

Choosing the right home coffee machine can feel overwhelming, with so many options available. Your ideal choice depends on your personal preferences, budget, and how involved you want to be in your daily brewing ritual. To help you make an informed decision, we'll break down the two primary considerations when buying an espresso machine:

1. Boiler vs. Thermoblock heating systems.
2. The importance of your coffee grinder

Boiler vs. Thermoblock Coffee Machines: The Core Difference

The main difference between different domestic machines is whether it uses a thermoblock or a boiler to heat up the water and steam.

Boiler coffee machines are normally found in commercial settings and the below explains why. You can get smaller boiler machines for domestic use but they are usually quite bulky and relatively expensive due to the heavy-duty materials like copper used for the internal plumbing. 

Here's how they generally work:

• Heating Process: Water is heated in a pressurised boiler (usually 1-2 litres) to approximately 120°C, generating about 1 bar of steam pressure above atmospheric pressure.
• Cold Water Path: Cold water from a separate tank is pumped at high pressure through a spiraled metal tube inside the boiler. This heat exchange brings the water up to the ideal brewing temperature, aiming for around 97°C as it exits towards the group head.
• Hot Water Dispensing: Hot water for a dedicated tap is drawn directly from the lower part of the boiler. The steam in the boiler above the water level pushes the water out. The water going to the hot tap is hotter than 100 deg C and if it does not cool down enough, it comes out very steamy. The steam for steam wands is taken from the top of the boiler. 

Potential Considerations for Boiler Machines

While robust, boiler coffee makers can present some challenges regarding temperature stability:

• Temperature Control: Most rely on a mechanical, spring type, pressure sensor to indirectly gauge boiler temperature, which can lead to inconsistencies as they are not the most accurate. Smaller machines with powerful heating elements might experience temperature "overshoots," making the water too hot.
• Heat Loss: Draining significant hot water can cause the boiler to lose too much heat, impacting subsequent shots.
• Flow Rate Dependency: The final temperature of water reaching the group head is highly dependent on flow rate. Issues like pump wear, blockages in the group head restrictor, or even simply pulling too much water can significantly affect brewing temperature.
• Warm-up Time: A major point to note is the warm-up time. Heating the large mass of a boiler and its water can take 15-20 minutes at full power. Often, the group head itself isn't fully warm, requiring a "dummy shot" to reach optimal extraction temperature.

Exploring Thermoblock Coffee Machines

Thermoblock coffee machines offer a different approach to heating water, with several distinct advantages:

• Rapid Warm-Up: A significant benefit of thermoblock espresso machines is their speed. They typically heat up within 1-3 minutes, meaning less waiting for your morning coffee.
• Integrated Heating: The thermoblock is often integrated directly into the group head, ensuring the group head itself heats up quickly enough for a decent first shot.
• Precise Temperature Control: Thanks to advanced, fast-responding electronics, the group water temperature in a thermoblock system can be highly accurate and stable, especially in more expensive models.
• Energy Efficiency: They generally use less power because they only heat water on demand, rather than maintaining a large volume of hot water constantly.
• Durability & Repairs: With less material exposed to high forces, thermoblock machines should theoretically have fewer parts prone to breaking. However, their compact size can sometimes make repairs more challenging if a component does fail. Like all machines, regular cleaning and occasional group head seal replacement are essential for maintenance.
• Temperature Adjustability: Many thermoblock machines allow users to easily adjust the temperature, offering flexibility to suit different coffee types and taste preferences. Some even display the extraction temperature. Our experience with brands like Ascaso suggests excellent and consistent shot quality, aided by continuous improvements in electronic components.

So what is the advantage of a boiler machine?

The big advantage of a boiler machine is that it has a lot more steam power and it is readily available, once the machine is warmed up.

On a cheaper thermoblock machine there is often only one thermoblock. When switching from making a coffee to steaming, the themoblock needs to heat up from say 95 deg C to 165 deg C or so.  This takes a few minutes and is a bit annoying after just making a shot. If you want to make immediately thereafter another shot of coffee, the thermoblock needs to cool down, and often you will need to pass some water to have it cool down quicker. You can work around this by making first all your coffee shots and then do the steaming. 

A machine with a thermoblock for the coffee and another thermoblock for the steam, each with its own pump, is a lot more convenient. Then there is still the main disadvantage that the steam power of a thermoblock is almost never as good as from a boiler machine, although we have seen the steam power improve over the last decade.

If you want to do quite a bit of milk frothing, for example making drinking chocolates for the kids after you made your coffee, this can be a big disadvantage. However, for frothing a 600ml jug for 2 flat whites, the steam power on the more expensive machines is just enough, but the cheaper machines can struggle.  

When comparing Pump Systems there is often not much difference between boiler and thermoblock domestic machines as they often use similar vibrating pumps. However smaller thermoblock units tend to feature more compact pumps giving a little less pressure for the extraction. Vibrating pumps are more resilient against abuse, like running the machine dry, but rotary pumps are stronger and that is why larger commercial machines have rotary pumps.

This is the main issue to consider when deciding on what type of coffee machine to buy, apart from the grinder…. We will explain that one soon.