F37 Error in Ferroli boiler: causes and real solution

The F37 code on a Ferroli boiler appears when the circuit pressure drops below the minimum needed to operate normally. In practice, the boiler protects itself, cuts off the heating or hot water demand, and displays an alert that almost always points to the same cause: lack of water in the circuit or an incorrect pressure reading.

The correct response usually starts with a simple check of the pressure gauge and, if necessary, refilling the system until it is within the usual operating range, which on many models is between 1 and 2 bar. When the problem does not disappear after that operation, we are no longer talking about a simple home adjustment, but about a leak, a faulty filling valve, a defective pressure sensor, or a hydraulic fault that requires technical inspection.

If you have a problem with your boiler, you can use our free error code finder. From there, you will be able to find out and solve all errors easily and effectively.

What the F37 lockout really indicates

The warning is neither decorative nor arbitrary. F37 indicates insufficient water pressure for the Ferroli boiler to complete ignition safely. When the circuit loses charge, the pump, the heat exchanger, and the control elements operate outside their ideal range, and the unit stops before forcing sensitive parts. It is a preventive shutdown, not a mere electronic whim.

In everyday use, this behavior is noticed very clearly: hot water may take longer to arrive, the heating may cut out, or the panel may show the lockout even though the home has not visibly changed. Sometimes the pressure gauge had already been dropping for days; other times, the drop happens suddenly after bleeding radiators, after work on the installation, or after a small but continuous loss that goes unnoticed.

This code should not be interpreted as a serious fault on its own, although it is a sign that something in the circuit is operating below normal. In many homes, the issue is resolved without dismantling anything or replacing parts; in others, the same warning is the first symptom of a slow leak or a filling valve that no longer seals properly.

The correct pressure and why it matters so much

Most Ferroli domestic boilers operate within a pressure range that is usually between 1 and 2 bar, with a common reference point around 1.2 bar when cold. That figure is not a whim of the manufacturer. It is the range that allows water to circulate stably, avoid unnecessary trips, and maintain heat transfer without stressing the system.

If pressure falls below the minimum threshold, the safety system understands that there is not enough water column to operate normally. If the range is exceeded too much, problems also appear: the safety valve may discharge, the connections work under more stress, and the circuit loses balance. That is why the goal is not to fill without measure, but to leave the installation within its useful range.

In winter, when the heating operates for more hours, temperature changes and small expansions in the circuit cause the pressure to fluctuate. That movement is normal up to a point. What is not normal is a frequent drop or a reading that falls rapidly after you have corrected the level. That is often where the true origin of F37 is hidden.

How to restore operation without stressing the system

The first check should be carried out with the boiler in stable conditions, preferably when cold. The goal is to look at the pressure gauge or digital reading and confirm whether the value is below the expected minimum. If the needle or display shows pressure that is too low, the next step is to locate the filling valve or the equivalent water charging system built into the model.

On many Ferroli models, that valve is located at the bottom of the casing. It is usually opened gently and gradually. It is advisable to open it slowly, watch the pressure rise, and close it as soon as the circuit reaches a safe zone, normally around 1.2 to 1.5 bar. There is no point in leaving it much higher just to be safe. The circuit does not improve by having excess pressure; on the contrary, it can cause discharges or unnecessary overpressure.

Some models include a more convenient filling system, with a push-button or integrated valve, which makes the operation simpler. Even so, the logic is the same: introduce water until the correct range is restored, close the flow properly, and check that there are no drips. After that, a basic reset is usually enough to clear the warning if the problem was purely hydraulic.

When the boiler still shows F37

If the unit locks out again shortly after refilling the circuit, the fault is no longer in the filling action itself, but in what is causing the pressure loss or in what the system is reading incorrectly. That distinction is important because it avoids repeating the same operation over and over without resolving the real cause. Repetition tires the unit and does not correct the underlying issue.

One of the most common possibilities is a damaged or jammed filling valve. In that case, the boiler may seem to be filled, but the mechanism does not open or close precisely. The result is incomplete filling or a later loss that brings the fault back in a short time. The opposite can also happen: the valve may not seal and allow water to escape unnoticed.

Another very common cause is a slow leak in the circuit. There is not always an obvious puddle. Sometimes the problem is in a radiator, a threaded joint, the safety valve, or a part that drips so little it only leaves a dry stain or intermittent dampness. When pressure drops again and again for no apparent reason, checking every point in the installation is more useful than insisting on refilling.

The pressure sensor and the blind spot in diagnosis

When the boiler shows F37 but the circuit seems to have enough water, attention shifts to the pressure sensor. That component translates the hydraulic state of the system into a signal the electronics can understand. If it fails, the boiler may behave as if it lacks water even though the circuit is within reasonable parameters.

This type of fault makes diagnosis a little more complicated because the user sees an alarm that matches a lack of pressure, but the real cause is an incorrect reading. The pressure gauge can help distinguish one case from another. If the physical pressure is fine, there are no signs of leakage, and the error will not clear, the sensor or its connection come to the forefront. In that scenario, the repair usually requires expert hands, since intervening without clear criteria can worsen the fault or create a leak in a sensitive part.

The wiring should also be considered. A loose connector, a corroded terminal, or a poorly seated connection can cause the board to receive a false reading. It is a less visible fault than a leak, but just as capable of stopping the unit. Electronics, after all, only act on what they interpret; if they interpret it wrongly, they shut down for protection.

Signs that point to a hidden leak

Small leaks are a bit like a household saboteur. They make no noise, do not flood the floor, do not attract attention, and yet they slowly drain the installation pressure. The most common symptom is that the boiler works well after refilling, but days later it shows the same lockout again. That rhythm, almost metronomic, usually reveals a continuous loss.

At that point, the inspection should cover radiators, valves, joints, air vents, and the safety valve. A valve that discharges intermittently may leave traces of moisture or mineral deposits around the outlet. A radiator with a microleak, on the other hand, may show faint stains, corrosion, or a slight smell of dampness near the connection. None of that is always visible at first glance; that is why monitoring the pressure over hours or days provides valuable clues.

A useful approach is to check whether the drop occurs with the heating on, at rest, or even during the night. That pattern helps distinguish a thermal issue from a pure hydraulic loss. If pressure drops even when not in use, the installation is losing water somewhere. If it drops more with the heating running, there may be a valve behaving irregularly or a point that opens as the circuit expands.

When the problem stops being a domestic one

There are situations in which F37 is corrected once and never returns. In others, it repeats with a stubbornness that already signals a deeper fault. When the pressure drop is continuous, the filling valve does not respond, or the sensor keeps failing after the basic check, the sensible thing is to stop. Continuing to fill the circuit without resolving the cause only postpones the problem and may hide greater damage.

Any sign of visible dripping, corrosion, unusual noise, or discharge through the safety valve also deserves special attention. Those details indicate that the system is no longer working under stable conditions. A technician can measure the actual pressure, check the expansion vessel, inspect the circuit tightness, and verify whether the error comes from a mechanical part or from an incorrect electronic interpretation.

In a boiler, the line between a minor fault and a more serious one is not always obvious. Sometimes a simple poorly closed valve triggers the warning; other times, a small internal loss turns into repeated cut-offs and a higher repair bill if it is allowed to progress. That is why the criterion should not be to endure it until the boiler stops completely, but to act when the pressure starts behaving irregularly.

What helps prevent it from appearing again

Prevention in this case is not mysterious, but it does require discipline. Checking the pressure regularly, especially in the colder months, makes it possible to detect a drop before the boiler locks out. There is no need to obsess over it; a reasonable check and attention to any repeated drop, however small it may seem, is enough.

It is also a good idea to make sure the filling valve is fully closed after use. An incomplete closure can generate microleaks or a slow loss that is only detected when the system drops again. Likewise, annual maintenance helps prevent parts such as the safety valve, pressure sensor, or expansion vessel from deteriorating unnoticed. They are discreet components, but decisive ones.

In installations with hard water, limescale can wear moving parts faster. That wear does not always cause an immediate fault, but it does shorten the useful life of valves and leaves residue in areas where water should circulate freely. A clean, well-balanced circuit inspected in time prevents F37 from becoming a recurring and annoying visit.

A small alert that usually tells a longer story

F37 almost never appears by chance. Behind it is usually pressure falling because of wear, a valve that does not seal, a sensor that lies, or an installation that loses water through a fatigued gasket. The warning simply gives a name to an imbalance that had already been developing in silence, like a drop that takes time to be heard but eventually empties a glass.

The best way to read the problem combines calm and method. First, check the pressure. Then refill with judgment. Later, observe whether the system remains stable or drops again. And, if the pattern repeats, move from the household fix to a technical inspection. In a boiler, as in almost all home heating, time wasted chasing the symptom ends up costing more than addressing the cause.

That is why the value of this code is not only in knowing what it means, but in understanding what it is telling you about the circuit. F37 warns of a hydraulic weakness, and that warning deserves to be read precisely: sometimes all it takes is water; other times, it is necessary to find the leak, replace a valve, or correct a misleading reading before the system locks out again.