Comprehensive Guide to Boiler Filling Taps: Maintenance and Usage Tips

Typically placed under the boiler, it’s a tap that acts as a bridge between the water supply and the heating circuit. It’s used to charge the system to a pressure of 1.2bar / 1.5bar.

Use this filling tap to restore the pressure of the heating system. The tap should normally be CLOSED to prevent overpressure phenomena.

If the pressure accidentally exceeds 2 bar (with the system cold), once the system filling tap is closed, you can discharge the excess pressure through the radiator air bleed valves.

Pressure checks should be carried out every 2-4 months to prevent the thermal generator (boiler) from operating at zero pressure, causing malfunctions.

If the system requires filling more frequently (about every 1-2 weeks), it may be necessary to check for any leaks or drips under the boiler or at the radiators.

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Automatic Filling

Automatic filling is prone to problems, much depends on the state of the circulating technical water. Indeed, in particularly muddy systems, it can get blocked. This valve, like the traditional one, forms a bridge between two circuits: the heating and the sanitary water. Therefore, there are different impurities from the two circuits and a relatively more sophisticated mechanism.

Impurities in the Heating Circuit

Given that the heating system, if it consists of radiators, will always produce impurities over the years. These impurities can block the automatic filling mechanism. In traditional heating, it is mainly oxides and sludge. Both cast iron and aluminum radiators contribute to their formation. Conversely, in underfloor heating, there are issues about algae. The temperatures of underfloor heating help the proliferation of microorganisms. The only systems to improve the quality of the technical water in underfloor heating are algaecides. Treatment to be carried out at least once every 15 years. These algae can severely test the automatic filling mechanism.

Impurities in the Sanitary Water Circuit

On one hand, we have the technical heating water, and on the other, the sanitary water circuit. This latter circuit can also have impurities, the main one being limestone. In regions where the water is particularly hard, limestone can block the mechanism. Another problem is the rust that can form in very old pipes. Some systems have iron pipes and rust flakes are a common occurrence.

The Type of Blockage

The automatic filling valve can get blocked in two ways, closed or open. If the valve is blocked closed, it’s not too bad, the system doesn’t fill and soon it’s replaced. Conversely, if the valve is blocked open, the heating circuit becomes overpressurized. Subsequently, the safety valve opens and starts leaking. When there is automatic filling, there is no end to the loss. Besides taking away the valve itself, which will no longer close as before, there’s a serious risk of flooding.

Manual Filling

Manual filling can also have problems, however, they are less than those with automatic filling. Modern manual valves have an integrated non-return system, consisting of a spring-loaded shutter with a membrane. It’s not uncommon to find blocked mechanisms, indeed, this feature constitutes a common bottleneck. Once, these valves were very simple and the passage was free. Often in systems poorly served by the water supply in terms of flow, it was not rare for the user to forget the filling tap open. It still happens now, but at least the valve offers resistance to the passage, protecting the heating circuit.

Charging Pressure on Euroterm Boilers Year 1996

Locate the green-colored tap as shown in the photo, you can find it on the lower part of the boiler. Normally, this tap is accessible through a hole cut in the sheet metal.

The photo shows the tap in the OPEN position, in this position the water flows from the water supply to the system of cast iron radiators or aluminum radiators.

Always remember to close this tap at the end, that is, upon reaching a pressure of 1.5 bar in a preferably cold system.

If the tap remains open without supervision, it can lead to overpressure phenomena in the system. At 3bar, the safety valve starts to lose water and the boiler drips.

Questions and Answers

The system pressure is higher than 2.5 bar!

It’s too high! Release the pressure from an air purge valve of any radiator!

Did you close the filling tap when you filled the system? It’s extremely important to always close the filling tap at the end of charging.

If the filling has remained open, no matter how much you empty the system, it will always return to over 2.5 bar.

The system pressure increases a lot when the radiators are hot!

If there’s a significant pressure difference from radiator off to radiator on, it may mean that the expansion vessel of the boiler heating is deflated or punctured. Contact your boiler maintainer to arrange regular maintenance. If maintenance has already been carried out recently, it may be that the air chamber of the heating expansion vessel is punctured.

Note well that if the pressure difference is about 0.5 bar from off or on then it’s perfectly normal. This is an effect of the expansion of the system’s water. Otherwise, contact your trusted technician.

The boiler pressure rises rapidly to 3 bar when just turned on and the boiler makes noise

Something is preventing the technical water from circulating, it’s not about the filling tap if at rest it’s at the correct pressure. Probably the circulator is stopped or there’s an obstruction that causes the water to vaporize and quickly raise the pressure. Turn everything off and contact your trusted technician.

The boiler pressure lowers every day

There can be several reasons:

• There’s a hidden leak in some radiator valve or among the elements: in this case, carefully check each radiator with your hand at the joints looking for moisture.
• There’s a leak in the boiler: Check carefully that there are no visible drops under the appliance.
• You’ve just turned on the heating: Maybe it’s just air, note the day and time when you filled, if it’s already the sixth time you’ve added water and don’t perceive visible leaks, contact your trusted technician.
• You’re on the ground floor: It often happens that the pipes on the ground floor are under the floor. For some reason, they are not insulated and if they are made of metal, they can be corroded releasing water from the radiators. This happens due to unisolated and unclad iron pipes.
• The expansion vessel is too inflated / deflated / punctured: In this case, as soon as you open the charging tap, the pressure gauge instantly jumps in pressure. It may be that you need the equivalent of half a cup to reach the operating pressure. Just as little water goes a minimal air vent brings it back to zero. Contact your trusted technician.