Filling valve

Usually placed under the boiler, it is a faucet that bridges between the water main and the heating circuit. It is used to charge the system to a pressure of 1.2 bar / 1.5 bar.

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

If the pressure accidentally exceeds 2 bar (with the system cold), once the filling valve is closed, you can release the excess pressure through the air vent valves on the radiators.

Pressure checking should be done every 2-4 months to prevent the heat generator (boiler) from operating at zero pressure, causing malfunctions.

If the system requires more frequent refilling (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, heavily depending on the condition of the circulating technical water. In fact, in systems particularly dirty with sludge, it can become blocked. This valve, like the traditional one, forms a bridge between two circuits: heating and domestic hot water. Thus, there are different impurities in the two circuits and a relatively more sophisticated mechanism.

Impurities in the Heating Circuit

Considering that the heating system, if consisting of radiators, will inevitably produce impurities over the years. These impurities can block the automatic filling mechanism. In traditional heating, these are predominantly oxides and sludge. Both cast iron and aluminum radiators contribute to their formation. Conversely, underfloor heating systems face issues with algae due to the temperatures conducive to microbial growth. Algaecides are the only means to improve the technical water quality in underfloor heating, needing treatment approximately once every 15 years. These algae can severely challenge the automatic filling mechanism.

Impurities in the Domestic Hot Water Circuit

While we have technical heating water on one hand, on the other hand, we have the domestic hot water circuit. This latter circuit can also have impurities, primarily limescale. In regions with hard water, limescale can block the mechanism. Another problem is rust that can form in very old pipes. Some systems have iron pipes, and rust flakes are a daily occurrence.

The Type of Blockage

The automatic filling valve can block in two ways, closed and open. If the valve is closed, it’s not a big issue; the system won’t fill, and replacement is imminent. Conversely, if the valve is stuck open, the heating circuit will be overpressurized. Subsequently, the safety valve will open and start leaking. With automatic filling, the leak won’t stop. Moreover, besides the valve no longer closing properly, there is a serious risk of flooding.

Manual Filling

Manual filling can also present problems, but they are generally less than with automatic filling. Modern manual valves incorporate a non-return system, consisting of a spring-loaded membrane shutter. Blocked mechanisms are not uncommon; in fact, this feature is a common bottleneck. These valves were once very simple, with unrestricted flow. Often, in systems where water supply is inadequate, users would forget to close the filling valve. This still happens, but now the valve offers resistance to flow, protecting the heating circuit.

Loading Pressure on Euroterm Boilers Year 1996

Identify the green valve as shown in the photo; you can find it on the underside of the boiler. Normally, this valve is accessible through a hole cut in the sheet metal.

The photo shows the valve in the OPEN position; in this position, water flows from the water main to the radiator system, whether cast iron or aluminum.

Always remember to close this valve when finished, preferably when the system reaches 1.5 bar pressure, preferably cold system.

If the valve remains open unsupervised, the system may experience overpressure. At 3 bar, the safety valve starts leaking water, and the boiler drips.

Questions and Answers

The system pressure is over 2.5 bar!

It’s too high! Release the pressure from any radiator air vent!

Did you close the filling valve after filling the system? It’s crucial to always close the filling valve after completing the filling.

If the filling remained open, no matter how much you drain the system, it will always return above 2.5 bar.

The system pressure rises significantly when the radiators are hot!

If there’s a noticeable pressure difference from a cold to a hot radiator, it could mean the heating expansion vessel of the boiler is deflated or punctured. Contact your boiler maintenance technician to arrange for routine maintenance. If maintenance has recently been done, the heating expansion vessel’s air chamber might be punctured.

Note that a pressure difference of about 0.5 bar from cold to hot is perfectly normal. It’s due to water expansion in the system. Otherwise, contact your trusted technician.

The boiler pressure rapidly rises to 3 bar when just turned on, and the boiler is making noise

Something is preventing the technical water from circulating; it’s not related to the filling valve if it’s at the correct pressure when idle. The circulation pump may be stuck or there could be an obstruction causing water to turn to steam and rapidly increase pressure. Turn everything off and contact your trusted technician.

The boiler pressure drops every day

There could be several reasons:

• There’s a hidden leak in a radiator valve or between the elements: In this case, carefully check each radiator for dampness around the joints.
• There’s a leak in the boiler: Check carefully for any visible drips under the appliance.
• You’ve just turned on the heating: It might just be air; note the day and time of each fill. If you’ve already refilled six times without visible leaks, contact your trusted technician.
• You’re on the ground floor: Ground floor pipes are often under the floor. If not insulated for some reason, metal pipes can corrode and release radiator water. This is due to uninsulated and unjacketed iron pipes.
• Expansion vessel too inflated / deflated / punctured: In this case, as soon as you open the filling valve, the pressure gauge instantly jumps. Perhaps the equivalent of half a glass to achieve the operating pressure. As little water as a minimal air purge brings it to zero. Contact your trusted technician.