Limescale build-up is one of the worst things to happen to any coffee machine, much worst than a dirty machine. They form solid obstructions from the inside and can cause severe damage when the sensors are hindered. That could cause the machines to overheat unnecessarily, causing collateral damage to several components.
The advice stated on this page applies mainly to professional machines with a boiler. For coffee machines purchased from the electro marts, like Nespresso, Delonghi, Krups, etc. They may work differently and require other instructions, which you are strongly advised to follow the instructions from the manufacturers. But they probably work closer to the concept of Single Boilers, except it has no boiler but still relies mainly on thermostats for safety.
How does descaling work?
Limescale is mainly magnesium and calcium. Most of the limescale could be dissolved with acid. For the case of an espresso machine, you will need to use a descaler that is food safe. Citric acid is often used for descaling, but it only works well when the solution is hot.
Feeding hot descaling solution into the hot water tank can cause damage to the inlet water connections that are only designed to transfer cold water. For example, silicone tubes connected to brass fittings can come off when hot water passes as the brass fitting will expand from the heat and release the grip on the tubes, causing them to come off and cause major leaks.
The best descaler is one that is safer for the yellow metal and works cold; the Puly Caff Liquid Descaler for Espresso or Coffee Machines is what we use professionally.
Is it a good idea to descale often?
No, unless you are using water that is very hard and has formed a lot of limescale. Then it will be the lesser devil to use a descaler since a machine full of limescale can be unsafe.
Descaling is not something you will want to do often because it is corrosive. It erodes yellow metal and causes the lead in brass to leach. Brands like Bezzera will try to use the safest food-grade brass they can find with little or no lead. Lead is needed in brass to keep them more machineable.
Will I still have limescale issues if my boiler is made of stainless steel?
Of course, the limescale sticks to almost anything. We have even seen them stick on Teflon coating. Some believe that stainless steel boilers may reduce the amount of limescale formed, but we don’t see any evidence of that, as we often see limescale forming on stainless steel surfaces.
Even if the boiler is made of stainless steel, the fitting and pipings are usually brass and copper. This is where the limescale usually forms and creates obstruction issues.
The start-up time will be incredibly long and inefficient if the connecting tubes are fully stainless steel, as stainless steel is not a good conductor of heat. Maintaining temperature stability will be extremely difficult as the heat will have colossal difficulty spreading evenly across all surfaces.
Stainless steel boiler is usually used for big and heavy boilers as it has a more robust structural strength to take its own weight; only in this aspect, it has more functional benefits in an espresso machine.
Does descaling works?
The above shows a heat exchanger boiler. It works only to a certain extent. It can only clear off limescale where the descaling solution can reach. The boiler is never full of water for heat exchangers or steam boilers. It leaves some space on top of the boiler for steam to build. However, limescale can build up anywhere, including at the top of the boiler.
The photo above shows that the most critical sensors and safety are on top of the boiler. In total, there are four safety mechanisms. They are the water sensors, safety valve, pressure sensor and thermostat, which is located below the boiler.
The pressure sensor, though located away and on top of the boiler, is often affected by limescale formation. When it is blocked, the machine will not sense enough pressure and keeps heating until the safety valve or thermostat activates.
A photo of the pressure sensor with limescale blockage.
How much can I descale doing it myself?
That depends on the type of boilers you are using.
Heat Exchanger boiler
This is the most common type of boiler used for professional espresso machines. They are efficient and give fresh water for extraction every time. Also can froth and extract simultaneously.
Such boiler system has two sections in the boiler. There’s a heat exchanger compartment in the steam boiler. It’s a boiler in a boiler. You can’t descale the top of the steam boiler using the standard instructions for filling and rinsing. This means that even if you descale, you may have some false assurance that your machine is safe as the sensors can’t be adequately cleaned.
However, you can descale the path from the water tank to the grouphead. This should descale the heat exchanger section, which could reduce brew pressure issues. Descaling steps for descaling just the heat exchanger can be found here: Puly Caff Liquid Descaler for Espresso or Coffee Machines
Double boilers have two separate boilers. It’s the same issue for the steam boiler. You can only better descale the brew boiler.
Typically, the brew boiler has no safety valve or pressure sensors, as this section has to be overfilled all the time. Inlet pressure from your water tank or pipes should not be sufficient to cause the boiler to explode, but if the heating goes haywire and heats non-stop. The only protection left is the thermostat.
Single boiler is an exception. It only has one boiler. This can be descaled to a greater extent, but the machine typically doesn’t have many safeties to start with. As the boiler is often overfilled, a pressure sensor and a safety valve that works by sensing pressure can’t be installed. It can only rely on the thermostat, which can fail like any electronics.
Since single boilers are often accompanied by heat stability issues and are cumbersome to make milk recipes like lattes or cappuccinos, they are getting less popular. The main reason people may still get them is they are slightly cheaper. They are gradually being replaced by heat exchangers, which provide a much better heat profile beneficial to extraction.
Can I check if my machine has limescale?
Even technicians can’t see the inside of piping and boilers. If you use the water wand a lot, you can unscrew the nozzle and check for sediments and limescale.
If a brass fitting takes in water, you can dry it up and see if there are limescale marks.
However, those methods can’t tell you how much limescale is in the machine and whether the condition is critical. The best thing to do is to leave it to the professionals who should check the pressure sensors and some of the safeties.
What’s the best way to treat limescale?
By now, you should know that descaling the top of the boiler is where it matters, and descaling is corrosive.
There are two ways to get it done correctly, and only professionals can do them.
Dismantle and fully descale
This is tedious, time-consume and costly.
A good thing about this is it is more thorough in cleaning the fittings as you can examine each part. However, you can’t descale parts that have attached electronics like the pump, pressure sensor, etc. You still can’t be sure that the sensors are fully working, whether it has hidden limescale, worn gaskets or reaching their end of life. So most likely, the technicians will advise you to replace additional parts on top of the complete descaling. This can total up to cost at least 1/2 the machine, a very expensive approach.
Another problem is that you can expect a lot of corrosion, which is not reversible.
Replace only the affected components.
If the water hardness is not as hard as what we see in Singapore, we don’t think it is necessary to do a full descale. As it’s not the thin layer of limescale sitting at the bottom of the boiler that you are trying to get rid of.
You can replace only the affected component to give you better assurance that the parts are working and not affected by limescale. All valves and parts also have a limited lifespan, so it’s inevitable that they must be replaced. This should give you a more thorough fix.
Limescale will still be left in the boiler, but the main paths can mostly be cleaned when descaling the heat exchanger. Remember that the descaling is corrosive and causes the metal to leach into your drinks, so we usually advise doing it only if you think it’s necessary.
What’s the best thing to do?
The best thing to do is to keep limescale from building up in the first place. It will save you a lot of monies in the long run.
We wrote a detailed article here. Water Softening.
It would help if you regularly drained the steam or heat exchanger boiler. This reduces the concentration of limescale residing in the boiler. Instructions can be found here: Troubleshooting Guide for Professional Espresso Machines
If your machine already has some limescale, which is not unusual. You can retard the speed of further formation with the help of water softeners. So it’s never too late until you already have a big problem that requires a fix.
If you want to descale just the heat exchanger boiler, instructions can be found here: Puly Caff Liquid Descaler for Espresso or Coffee Machines
If you are concerned or already having issues, it’s best to let a qualified technician check the machine and replace some critical components. The technicians cannot see inside the boiler but can check if the pressure sensors are blocked or perform basic function tests.
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