As an espresso enthusiast, I want to know what features are worth the extra money. That led me to research whether mechanical thermostats or PID machines are worth the extra money. Here are my findings.

I’ll summarize which is better and then explain what each heating type is. Afterward, I’ll explain the pros and cons of using each heating type.

Here in an overview:

Let’s get to it.

Key Takeaways

Mechanical thermostat machines cost less than ones with PID controllers.
Milk will also cause coffee temperature to fluctuate, no matter whether you use PID.
PID controllers are best for coffee makers with dual boilers.
Mechanical thermostat machines are an ideal choice for most home baristas.

Is a PID or Mechanical Thermostat for Espresso Machines Better?

Mechanical thermostat espresso machines will work best for most folks, since you’ll likely add milk to your drinks, anyway. An additive that would otherwise fluctuate your drink’s temperature.

Opt for a PID espresso machine in one of these scenarios:

You own a coffee shop: You want consistency with your drinks.
Buy a machine with a dual boiler: A PID will heat the milk and water; thus, no fluctuations.
You’re a perfectionist: You want your drinks to have precise temperatures.
You have disposable income: Such a feature could add hundreds to a machine’s price tag.

Some machines are “hybrid.” For example, the Profitec 300 is a dual boiler machine that uses PID to heat the water and a thermostat for the milk steam. This gives you less control over the pressure and steam temperatures, despite the listing saying it has a PID controller.

You could also install your own PID controller using a kit or a DIY option like an Arduino [1]. The kits cost more than $150 from what I’ve quoted. This means getting a machine with PID is the cheaper route.

It depends on your mechanics savvy and whether you want to go through the extra effort to optimize your espresso making.

Keep reading if you’re scratching your head and wondering what a PID is.

Summary: Unless you’re an espresso enthusiast, get a machine with a mechanical thermostat. And if you do get a PID, getting a dual boiler machine will reap the most benefits.

What Is a PID Temperature Controller?

A Proportional Integral Derivative (PID) controller acts like a digital thermostat for your espresso machine. It turns the heating element on and off but doesn’t cool your machine. It’ll power on and off several hundred times a minute to achieve your desired temperature.

Think of it like cruise control in a car. It keeps adding gas to your car but never brakes.

Many manufacturers will include PID controllers in single and double-boiler machines or heat exchangers.

In case you still don’t get what I wrote, here’s a further breakdown of the algorithm that PID machines use:

Proportional (P): Adjusts power to the heating element based on the difference between the current and set point temperatures.
Integral (I): Eliminates steady-state error by accumulating and adjusting power based on the error over time.
Derivative (D): Anticipates the rate of change of temperature and adjusts heating accordingly to prevent overshooting the set point.

Let’s check out the pros and cons of using this heating type.

Summary: PID controllers continually power your machine on and off to manage its temperature.

Advantages & Disadvantages of PID Temperature Controllers

Pros:

Minimum maintenance: Don’t need replacements or fixing as much.
Accurate: Can achieve an accuracy of 0.1% for flow and temperature.
Consistent: Will always keep temperature at a specific point.

PID controllers will provide fewer temperature swings above and below your set temperature. This will help you get the best temperatures out of your drink. And since they don’t rely on a bimetallic strip like mechanical thermostats, you won’t need to replace it as often.

Cons:

Doesn’t work well with heat exchangers: PID doesn’t control extraction temperature.
More expensive: Machines with this feature cost more than other heating types.

I said earlier that PID controllers work best for machines with dual boilers. Because with single boilers, you’re typically going for a budget machine. And PID controls the water temperature inside the heat exchanger. It doesn’t affect the water temperature as you’re extracting.

Let’s check out whether mechanical thermostats are better.

Summary: PID controllers are the most accurate and consistent temperature management component in espresso machines. But they’re expensive.

What Is a Mechanical Thermostat?

A mechanical thermostat for an espresso machine is a set of electrical contacts (bulb and capillary. These bimetallic strips have different ratings (e.g., 212 °F). Machines use it to maintain and control the water temperature on an analog brewer.

How does it work?

High pressure builds up inside the bulb once the water inside your machine reaches a specific temperature. The pressure then forces hydraulic fluid through the capillary. Then, from the capillary to the contacts.

This fluid comes in contact with the heating element’s circuit and causes it to power off.

If you have water below a specific temperature, the bulb has less pressure. Any exerted fluid will return to the bulb and close the contacts.

Are mechanical thermostats any good?

Summary: Mechanical thermostats power your machine on and off depending on the temperature.

Advantages & Disadvantages of Mechanical Thermostats

Pros:

Affordable: More accessible to espresso lovers on a budget.
Easy to repair: Fewer electrical components.

Espresso machines with mechanical thermostats will save you money while getting the job done. And though they don’t last as long as PID, they’re simpler to replace since they don’t have as many components.

Cons:

Heating element can overshoot: By 8–10%—otherwise known as deadband [2].
Heater won’t turn back on: Until the heater cools by about 10%
Temperature surfing: You’ll need to guess when the machine is at ideal temperature.
Not as durable: May need replacements more often.

Mechanical thermostats rely on a bimetallic strip that bends and straightens to control electricity flow. This constant flexing could eventually lead to your component failing. This isn’t an issue that PID controllers deal with.

The temperatures within machines with mechanical thermostats can overshoot by 8–10%. Meaning you won’t have a reliable gauge on your machine’s temperature. Since your machine’s not constantly monitoring its temperature, it’ll take longer for the heating element to power on again.

That’s all, folks.

Summary: Machines with mechanical thermostats cost less, but aren’t the most accurate.

Conclusion

Mechanical thermostats work better for most people because they’re affordable and “do the job.” PID controllers shine in dual boiler machines, where it would heat the milk and water. Because otherwise, the added milk would cause a temperature fluctuation in your drink.

Learn more about espresso machines by checking out our other guides.