Wear and tear and lack of maintenance are just two of the many factors that cause a water leak from the boiler. It is a problem that must be addressed immediately to prevent it from getting worse and to continue using its functions.

Why is the boiler leaking water?

To find out the reason for the unexpected, it should be remembered that the causes of the leak can be different.

• It may happen that the boiler loses water even when it is off. In this case, seals and fittings must be carefully checked and it must be ensured that there is not any break in the pipes.
• In fact, if you notice a slow but constant leak in the form of dripping, it is very likely that the problem comes from the drain pipe or the connected tap. It is then necessary to replace them and evaluate the condition of the relative gaskets.
• If, on the other hand, the leak is large, then the leak is linked to the boiler’s pressure which is too high. When it reaches excessive levels, the relief valve opens to allow the excess water to overflow. The pressure must be between 1.2 and 1.5 bar: just observe the values indicated by the pressure gauge for its monitoring.
• On the contrary, it may happen that the water loss derives from a pressure which is too low. This is another case in which, for example, the boiler loses water when it is off: it shuts down and the pressure drops. To intervene, the air can be eliminated from the circuit by venting the radiators.

Identifying the exact reason for the water leak is therefore difficult and relying on the skills of a specialised technician is the best solution.

How to fix a leaking pressure relief valve

Among the components of the boiler, the safety valve is the element that regulates the pressure and prevents it from being damaged by the other components. It is also identified as a relief valve. Since it serves to regulate the pressure, when it loses water it means that the problem is related to the latter.

Considering that the optimal range is between 1.2 and 1.5 bar, if the pressure reaches a value that exceeds the maximum limit of 3 bar, the valve discharges the excess water to keep the circuit in good condition.

It is possible to lower the pressure level by acting on the radiators, through the vent valve. Otherwise, by activating the filling loop, usually positioned at the bottom of the boiler, water is introduced and therefore the pressure rises. The pressure gauge allows you to understand what level it has reached.

Intervening on the safety valve is a delicate operation and an inspection by a qualified technician is therefore necessary.

Why is the relief valve leaking?

As seen previously, there are many causes for water leaking and this also applies to the safety valve.

• The origin of the problem may in fact depend on the expansion vessel, a component which keeps the pressure stable. Specifically, it absorbs the increase in pressure caused, in turn, by the increase in temperature and volume of the water. If the membrane inside the expansion vessel, which allows the absorption function, has a puncture, it cannot contain and control the increase in pressure. This eventuality occurs when the boiler is in operation and not when it is off.
• On the other hand, the exchanger may be punctured, too. Inside the exchanger, both the water from the heating circuit and that for the production of domestic hot water flow without coming into contact. If the plates inside the exchanger are punctured, the two circuits mix with a consequent increase in pressure. The relief valve thus operates to bring the pressure level back to an optimal range, i.e. below 2 bar.
• Then there is the hypothesis of a malfunction of the filling loop, which allows water to enter from the water mains to increase the pressure when it is too low. However, when the filling loop, once closed, does not interrupt the passage perfectly, the water from the mains water continues to enter the boiler slowly. Encrustation and limescale affect the state of the loop and its seals.
• Limescale can always compromise the inside part of the valve: thus water droplets are formed and come out of the component. It is the signal that the time has come to replace the safety valve.

Can a boiler explode?

Faced with unforeseen events such as water loss, the fear is that a highly dangerous accident could occur: the explosion of the boiler.

The boiler can actually explode, but the reason is to be found in the lack of maintenance, cleaning and combustion controls which measure the quantity of gases present in the combustion.

The resulting risks are mainly four.

1. In case of gas or LPG boilers, the gas leak can lead to poisoning due to inhaling harmful substances and to an explosion.
2. Without good ventilation and in the presence of a blockage of the flue gas pipes, the probability of the formation of carbon monoxide, an odourless and potentially fatal gas, increases.
3. Short circuits in electrical systems can cause fires involving the boiler.
4. The fire can directly involve the boiler’s fuel, if it runs on diesel or kerosene.

Water leaking, therefore, does not represent an extreme risk factor. On the other hand, the best way to avoid any unexpected event, small or large, with your boiler, is to proceed with the necessary maintenance and periodic checks, relying on the hands of an expert technician.