Ferroli boiler error F37: causes and the real solution

The F37 code on a Ferroli boiler appears when the pressure in the system drops below the minimum required for normal operation. 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 underlying cause: a lack of water in the system or an incorrect pressure reading.

The correct response usually starts with a simple check of the pressure gauge and, if necessary, topping up the system until it reaches the usual operating range, which on many models is between 1 and 2 bar. When the problem does not disappear after this, we are no longer dealing with a simple domestic adjustment, but with a leak, a faulty filling valve, a failed 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 can identify 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 system loses pressure, the pump, heat exchanger and control components operate outside their ideal range, and the unit stops before putting sensitive parts under strain. It is a preventive shutdown, not simply an electronic whim.

In everyday use, this behavior is very easy to notice: hot water may take longer to arrive, the heating cuts out or the panel displays the lockout even though nothing visibly appears to have changed in the home. Sometimes the pressure gauge had already been dropping for days; at other times, the drop happens suddenly after bleeding radiators, work has been carried out on the system or a small but continuous leak has gone unnoticed.

It is not advisable to interpret this code as a serious fault in itself, although it is a sign that something in the system is operating below normal. In many homes, the incident 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 as it should.

The correct pressure and why it matters so much

Most domestic Ferroli boilers operate within a pressure range that is usually between 1 and 2 bar, with a common reference point of around 1.2 bar when cold. This figure is not an arbitrary choice by the manufacturer. It is the range that allows water to circulate steadily, prevents unnecessary shutdowns and maintains heat exchange without putting undue strain on the system.

If the pressure drops below the minimum threshold, the safety system understands that there is not enough water column to operate normally. If the range is exceeded by too much, problems can also occur: the safety valve may discharge, the connections are placed under greater strain and the system loses balance. That is why the goal is not to fill it without measuring, but to leave the system within its useful operating range.

In winter, when the heating runs for more hours, changes in temperature and the small expansions in the system cause the pressure to fluctuate. This movement is normal to a certain extent. What is not normal is a frequent drop or a reading that falls rapidly after the level has been corrected. That is usually where the true cause of F37 is hiding.

How to restore operation without straining the system

The first check should be carried out with the boiler in stable conditions, preferably when cold. The aim 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 filling system included with the model.

On many Ferroli models, this valve is located underneath the casing. It should usually be opened gently and gradually. It is best to open it slowly, watch the pressure rise and close it as soon as the system reaches a safe level, normally around 1.2 to 1.5 bar. There is no benefit in leaving it much higher as a precaution. The system does not improve by being overfilled; on the contrary, this can cause discharges or unnecessary overpressure.

Some models include a more convenient filling system, with a button or integrated valve, which makes the operation easier. Even so, the principle is the same: add water until the correct range is restored, close the supply 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 continues to display F37

If the unit locks out again shortly after the system has been refilled, the fault is no longer in the filling action itself, but in whatever is causing the pressure loss or in whatever is being read incorrectly by the system. This distinction is important because it prevents you from repeating the same operation over and over without solving the real cause. Repeatedly doing so puts strain on the unit and does not address the underlying issue.

One of the most common possibilities is a damaged or stuck filling valve. In this case, the boiler may appear to be pressurized, but the mechanism does not open or close accurately. The result is incomplete filling or a subsequent loss that brings the fault back in a short time. The opposite can also happen: the tap may fail to seal and allow water to escape slowly.

Another very common cause is a slow leak in the system. There is not always an obvious puddle. Sometimes the problem is in a radiator, a threaded connection, the safety valve or a component that drips so little that it only leaves a dry mark or occasional dampness. When the pressure keeps dropping for no apparent reason, checking every point in the system is more useful than continuing to refill it.

The pressure sensor and the diagnostic blind spot

When the boiler displays F37 but the system appears to contain enough water, attention turns to the pressure sensor. This component translates the hydraulic condition of the system into a signal that the electronics can understand. If it fails, the boiler may behave as though it is short of water even when the system is within reasonable parameters.

This type of fault makes diagnosis a little more complicated because the user sees an alarm that is consistent with low pressure, while the real cause is an incorrect reading. The pressure gauge can help distinguish between the two situations. If the physical pressure is correct, there are no signs of a leak and the error does not clear, the sensor or its connection becomes the main suspect. In that situation, the repair usually requires expert hands, since intervening without the necessary knowledge can make the fault worse or cause a leak in a sensitive component.

The wiring should also be taken into account. A loose connector, a corroded terminal or a poorly seated connection can cause the control board to receive a false reading. It is a less obvious fault than a leak, but just as capable of stopping the appliance. Electronics, in the end, only acts on what it interprets; if it interprets things incorrectly, it locks the system out as a protective measure.

Signs that point to a hidden leak

Small leaks have something of a household saboteur about them. They make no noise, do not flood the floor, attract no attention and yet gradually drain the pressure from the system. The most common symptom is that the boiler works properly after being refilled, but a few days later it displays the same lockout again. That almost metronomic pattern usually gives away a continuous loss.

At this point, the inspection should cover radiators, valves, connections, bleed valves and the safety valve. A valve that discharges intermittently may leave traces of moisture or mineral deposits around the outlet. A radiator with a micro-leak, on the other hand, may show faint marks, corrosion or a slight smell of damp near the connection. None of this is always visible at a glance; that is why monitoring the pressure over several hours or days can provide valuable clues.

One useful approach is to check whether the drop occurs with the heating on, while the system is idle or even in the middle of the night. This pattern helps distinguish a thermal issue from a purely hydraulic loss. If the pressure drops even when the system is not in use, the installation is losing water somewhere. If it drops more when the heating is running, there may be a valve behaving irregularly or a point that opens as the system expands.

When the problem is no longer a domestic one

There are situations in which F37 is corrected once and does not return. In others, it keeps coming back with an insistence that already points to an underlying fault. When the pressure drop is continuous, the filling valve does not respond or the sensor continues to fail after the basic checks, the sensible thing is to stop. Continuing to fill the system without solving the cause only postpones the problem and may conceal more serious damage.

Any sign of visible dripping, corrosion, unusual noise or discharge from the safety valve also deserves special attention. These details indicate that the system is no longer operating under stable conditions. A technician can measure the actual pressure, check the expansion vessel, inspect the system for leaks and determine whether the error comes from a mechanical component or from an incorrect electronic reading.

With a boiler, the line between a minor fault and a more serious one is not always obvious. Sometimes a simple tap that has not been properly closed causes the warning; at other times, a small internal leak leads to repeated shutdowns and a higher repair bill if it is allowed to progress. That is why the right approach should not be to hold on until the boiler stops completely, but to act when the pressure starts behaving irregularly.

What helps prevent it from coming back

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

It is also a good idea to check that the filling valve is completely closed after use. An incomplete closure can cause micro-leaks or a slow loss that is only noticed when the system drops again. In the same way, annual maintenance helps ensure that components such as the safety valve, pressure sensor and expansion vessel do not deteriorate without warning. They are discreet components, but decisive ones.

In systems with hard water, limescale can damage moving parts more quickly. This wear does not always cause an immediate fault, but it does shorten the life of valves and leaves deposits in areas where water needs to circulate freely. A clean, properly balanced system that is checked in time prevents F37 from becoming a regular and irritating visitor.

A small warning that often tells a longer story

F37 almost never appears by chance. Behind it there is usually pressure dropping because of wear, a valve that fails to seal, a sensor that is giving false readings or a system losing water through a tired seal. The warning simply gives a name to an imbalance that had already been developing silently, like a drip that takes time to be heard but eventually empties a glass.

The best way to approach the problem combines calm with method. First, check the pressure. Then, refill it carefully. After that, observe whether the system remains stable or starts to drop again. And if the pattern repeats, move from a simple domestic adjustment to a technical inspection. With a boiler, as with almost every part of home heating, time spent chasing the symptom eventually costs more than addressing the cause.

That is why the value of this code lies not only in knowing what it means, but also in understanding what it is saying about the system. F37 warns of a hydraulic weakness, and that warning deserves to be read accurately: sometimes water is all that is needed; at other times, the leak must be found, a valve replaced or a misleading reading corrected before the system locks out again.