In this article we are going to analyse the most common problems that occur in Domusa Sirena Mix Duo boilers. If you have a boiler of this type, do not miss the practical advice that we will be giving to learn how to recognise faults and their possible solutions. Knowing how your boiler works will help you understand it and will save you stress.
You will always be able to determine when it is a routine malfunction, or when it is a more serious problem and it is necessary to seek technical assistance. At the end, we will also offer you access to spare parts for Domusa boilers available at Suner.
Problem with the thermostat in Sirena Mix Duo boilers
A symptom of this problem may be that, regardless of the comfort temperature that you program for the boiler through the thermostat, the water in the boiler remains at a temperature that was not the one you indicated.
However, you have to start by taking something into account. The boiler will always remain at 60 °C even if there is currently no demand for hot water in the home. This is designed in such a way that, at the exact moment when there is demand, the user does not have to wait for the water to heat up.
Beyond the normal situation described in the previous paragraph, there may be problems with the thermostat in Sirena Mix Duo boilers. For example, if the hot water pump of the boiler does not work, and therefore that level of heat does not come out of the boiler, then the safety thermostat trips.
It is normal for the safety thermostat to trip in these cases. But you need to repair or replace the hot water pump, which is causing the problem.
Domusa Sirena Mix Duo FDe boiler: Fault in the DHW
The failures of DHW (Sanitary Hot Water) of a boiler can manifest itself in various ways and be due to various causes. One of the ways it manifests is, of course, that the hot water is not working properly. That is, the temperature of the water in the taps when you open them can automatically rise or fall in temperature randomly: you open the tap, and the water comes out hot, in seconds it can get cold, and then very hot, etc.
This is usually more noticeable in DHW services where the tap remains open for a longer time. For example, taking a shower or washing dishes is more noticeable than when you wash your hands for a few seconds. In these cases, you may also notice that on the boiler temperature gauge, the number jumps up and down from one temperature measurement to another in a matter of seconds.
Some causes of this malfunction in the DHW may be, for example, faults or mismatches in the hot water probe, or that air has got into the heating circuit/heat exchanger, and for that reason the water is not heated properly by default or by excess. Most often it is the latter. The solution is to remove the air using the trap located inside the boiler. Bleed it down and turn it down until it’s at 1.5 bar.
Radiators do not heat
If the boiler is a Domusa brand (or even other brands), the fact that the radiators are not heating can be a symptom of the presence of air in the system. If it were only this, the problem would be solved simply by purging the radiators , starting with the one closest to the boiler. But the fact that the radiators do not heat can also be due to other causes. For example:
- Problems with the thermostat that regulates the DHW. In the event that the problem is in the thermostat, it may be a matter of failure but it may only be that it has been installed incorrectly. You have to go to a technician.
- There may be a blockage or blockage that prevents the hot water from circulating and reaching the radiators properly. This may be the case especially if some radiators are hot and others are not. If so, it will not be enough to purge them, but you have to unclog the system.
- Problems with the DHW pump. The heating pump may be blocked and must be unblocked. It is better not to try to use it like that. You have to seek the help of a technician or try to unlock it yourself. The pump is unlocked as follows:
Use a wide blade flathead screwdriver and also wear gloves. In the pump you will find a kind of screw that is actually a plug. Unscrew it and put it in a safe place, where you won’t risk losing it. Insert the flat screwdriver and try to find the rotor shaft (it has a flat slot). When you manage to engage the screwdriver with the shaft, give it a few turns clockwise. Little by little you will feel it loosen. That’s good. Next, place the plug screw as it was at the beginning, and dry the water that has come out. This procedure should have unclogged the pump. If there is more than one heating pump in your boiler, apply this same procedure to the other.
Sometimes problems related to one or more radiators not heating can only arise when switching the boiler from summer mode to winter mode.
Operation makes excessive noise
Normally modern boilers are designed to make as little noise as possible. This is part of the comfort of your home. Therefore, when a boiler makes noise beyond normal expectations, it may mean that it has a problem. It will also all depend on the part or component that is emitting the excess noise.
For example, it could be the radiators. Sometimes when the boiler stops, a sound similar to hissing air can occur in the radiators, even though the circuit itself does not contain air. The noise can make an echo from one radiator to another. It frequently occurs in the Domusa Sirena Mix Duo HFD 30 boiler, which is the analog version (the digital one is the Mix Duo HFD e). There is noise if you close any of the radiators because you are not going to use it.
In these cases, what may be happening is an excess speed of water circulation through the circuits, and it is solved by regulating the speed of the pump. In fact, the speed of the heating pump can and should be regulated depending on the installation of the home and its specific needs (heat demand per metre and pipe diameters, number of radiators, etc.) If this is your case , and you have it, for example, at power 9, bring it down to power 6 and maybe everything will be resolved.
But the noise can come from other elements of the heating system. Here we briefly list some causes of noise and how to solve them:
- Vibratory type sound. It is one of the most common sounds and the simplest solution. Some brackets or fasteners may be loose and need to be tightened or adjusted. There may also be open compartments that need to be closed.
- Buzzing sound. It is normal for the boiler to hum a little. But if it becomes excessive, it may be due to a faulty heating element in the system.
- Knocking sound. Poorly adjusted or loose components. They have to be fastened or adjusted. Debris may also have accumulated in the heat exchanger. The solution would be to perform an energy discharge.
- Gurgling sound. It can be due to the presence of real air trapped inside the system, which can even cause the radiators to not heat well. The solution is to bleed the radiators.
- Drip-like sound. The sound of drops may be indicating that there are leaks in some component, either due to wear or because the pressure is too high.
The pressure rises on its own in the boiler
One of the most likely reasons for the boiler to increase pressure on its own is that the expansion vessel is faulty or has run out of air. You should check which of these two things is happening. To find out, press the release. If water comes out, that indicates that the expansion tank has broken, and you should replace it with a new one. But if, on the other hand, when you press the shell air comes out and not water, that means that the glass is not broken and you only have to fill it with air. To fill it with air you must do the following:
- Locate the expansion tank. At the top it has a valve with a cap, similar to that of a tyre. Unscrew the cap and connect the mouth of an inflator (a bicycle one works, but it has to have a pressure gauge). Before blowing air into the pool, remove the water pressure from the boiler circuit and leave it at zero, with the drain open. Blow air into the glass until the pressure reaches 1.5 bar. Remove the inflator and put the cap on the expansion vessel valve. Ready.
If the problem is in the expansion vessel, when the boiler temperature rises, the pressure will also rise, but when the boiler temperature drops, the pressure will drop. However, another possible problem can occur when the primary system (the hot water that circulates through the boiler and radiators) and the secondary system (the hot water that goes to the taps) communicate.
If the latter is the case, then the pressure will tend to rise even though the boiler is cold. In other words: at no time does the pressure drop. In this case, it is necessary to detect which element of the system is connected. It can be the DHW exchanger, the filler valve, etc. The solution is to replace the element that is damaged and that therefore allows communication between the two circuits.
The boiler loses pressure
The symptoms of a loss of pressure in the boiler are evident. You can see it on the board of the boiler itself: it marks less than its usual 1.2 bar. Then you add new water, the pressure maybe equalises, but despite that very soon it starts to lose pressure again. Perhaps you apply other routine measures, such as purging the radiators. Basically the loss of pressure in a boiler usually has one of these two reasons:
- Some breakdown or malfunction has caused the boiler heating safety valve to come into action and release pressure. Actually it is a smart measure that if there is any failure, the safety valve releases the pressure. That is its function: to let go of excess pressure and thus avoid greater evils.
- The pressure escapes through a leak, which can be located in the boiler as well as in the installation, or in both. Depending on the size of the leak, the pressure will drop less or faster. The larger the leak, the faster the pressure drop.
In other words, the pressure loss in the boiler, more than a problem, is a symptom of something else. The solution to the pressure loss would be to fix the problem that causes it. In these cases, it would be a matter of fixing the leak that exists in the boiler or in the installation, or detecting the reason that the safety valve has been activated, and resolving it.
Spare parts for Domusa boilers in Suner
Through the following link you can directly access the spare parts for Domusa boilers at Suner. You can buy them online, or you can also visit any of our company locations.
- Click here to access spare parts for Domusa boilers at Suner.
If you also need more technical instructions on Domusa Sirena boilers (in terms of installation and functions), through the following link you can download the manufacturer’s manual:
- Click here to download the manual of Installation and Operation Instructions – Domusa .