What Should Boiler Pressure Be? Fixing Low and High Pressure

The short answer to what boiler pressure should be: according to Vaillant's ecoTEC user manuals, the water pressure in a cold heating system should sit roughly between 1 and 2 bar. This guide is for homeowners and tenants in Antalya, Turkey who have noticed the pressure on their combi boiler dropping or climbing; it covers the correct range, how to top up when pressure falls, what to do when it rises, and when it is time to call an authorized technician, based on the official manuals.

What Does the Pressure Gauge Actually Show?

The figure on your boiler's display or front-panel gauge is not gas pressure. It is the pressure of the water in the sealed heating circuit made up of the boiler, the pipework and the radiators. If that circuit is not at the right pressure, the pump cannot circulate water properly and the boiler may shut itself down for protection. That makes the pressure reading one of the simplest and most useful things to check at home.

What Should Boiler Pressure Be?

The right value varies slightly by model. Vaillant's current Turkish user manuals state the following:

• ecoTEC pro: with the heating system cold, fill pressure should be between 1.0 and 2.0 bar (0.1–0.2 MPa).
• ecoTEC pure: the intended system pressure range is 0.8–2.0 bar; below 0.8 bar the system should be refilled.
• ecoTEC plus: if fill pressure is below 0.8 bar, the heating system should be topped up; the display also shows the minimum and maximum values.
• ecoTEC intro: refill when pressure falls below 0.5 bar; the target system pressure when refilling is 1.0–1.4 bar.

Every manual adds the same note: if the heating system spans several floors, a higher fill pressure may be needed, and you should ask an authorized technician. Take your reading with the boiler cold. In a running, warm system the water expands and the gauge reads a few tenths of a bar higher, which is perfectly normal.

Why Does Boiler Pressure Drop?

In a sealed heating circuit, a very slight drop over time is expected. A noticeable fall usually comes down to one of these causes:

• Bleeding the radiators: some water escapes along with the air, so pressure drops. Always check the gauge after bleeding.
• A leak in the system: small leaks at radiator valves, fittings, the connections under the boiler or pipes inside walls cause pressure to fall steadily.
• The safety valve has discharged: if pressure ran too high earlier, the safety valve may have released water; once the system cools, pressure then reads low.
• Expansion vessel problems: Vaillant's installation and maintenance manual includes a check of the expansion vessel pre-charge during servicing; when the vessel is not doing its job, pressure can rise when hot and fall when cold.

Pressure Below 0.5 Bar: Fault F.22

According to the ecoTEC pro manual, when fill pressure drops below 0.5 bar the boiler shuts down and the display alternates between fault code F.22 and the current pressure; the ecoTEC pure manual likewise says the unit goes into fault mode below 0.5 bar. At that point neither heating nor hot water works. F.22 is not an ignition or electronics fault; it simply means there is not enough water, and the fix is to refill the system.

How to Top Up Boiler Pressure

Vaillant's manuals describe topping up as something the user can do. The general sequence is:

1. If you don't know where the filling valve is, ask the authorized installer who fitted your boiler. On models such as the ecoTEC pro and pure, it sits on the underside of the boiler.
2. Open all radiator (thermostatic) valves in the heating system.
3. Open the filling valve slowly and add water while watching the gauge until you reach the required pressure.
4. Close the filling valve.
5. Bleed all the radiators, then check the pressure again and briefly top up if needed.
6. When you are done, make sure the filling valve is fully closed.

The manuals also warn that very hard, corrosive or chemically treated water can damage seals and water-carrying parts, so only suitable heating water should be added. We cover the bleeding step in detail in our guide on how to bleed radiators.

If Your Boiler Keeps Losing Pressure

Topping up once and then running for weeks without trouble is nothing to worry about. If you need to add water every few days, though, there is a leak somewhere. Constantly adding fresh water brings oxygen and limescale into the system, which can eventually cause problems with the heat exchanger and pump. At that point the leak needs to be found rather than the system refilled again and again.

Why Does Boiler Pressure Rise?

It is normal for pressure to climb a little above the cold reading while the boiler runs, because heated water expands. The problem is when it goes clearly above the recommended range. Common causes include:

• A filling valve left open or letting by: a valve that doesn't close fully after topping up lets mains water creep into the circuit, pushing pressure steadily upward.
• An expansion vessel that isn't working: the installation and maintenance manual lists a "faulty internal expansion vessel" among the possible causes of pressure-related faults. When the vessel's pre-charge is lost, it can no longer absorb the expansion of heated water.
• Water passing into the circuit from inside the boiler: in some faults, pressurized domestic water can cross into the heating circuit. Diagnosing this requires opening the unit.

What Happens Near 3 Bar?

The maximum operating pressure of the heating circuit on Vaillant ecoTEC boilers is 3 bar. According to the ecoTEC pure manual, above 3 bar the excess heating water is expected to discharge through the safety valve. If you see water coming from the discharge pipe under the boiler, this may be why. With the boiler cold, you can release a small, controlled amount of water from a radiator bleed valve to bring pressure back into range; if it climbs again, the underlying cause hasn't been fixed and you need a technician.

When Should You Call an Authorized Technician?

• Pressure drops every few days and you keep topping up
• Pressure rises on its own even though you haven't added water
• Water is dripping from the safety valve or from under the boiler
• F.22 comes back even after topping up
• You can't find the filling valve or don't feel confident using it

Checking the expansion vessel pre-charge, tracing leaks and working on internal boiler parts are jobs for an authorized technician. As an authorized Vaillant dealer in Antalya, Devka Doğalgaz checks pressure, the expansion vessel and the pipework together as part of our boiler maintenance service. For circulation problems caused by sludge in radiator systems, see our radiator heating installation service.

Practical Notes for Antalya

Antalya's heating season is short, so many boilers sit switched off for months. Checking the pressure, bleeding the radiators and topping up if needed before the first run of the season is the easiest way to avoid meeting F.22 on the first cold day. We've collected these checks step by step in our pre-winter boiler checklist.

Safety Warning

Water pressure problems do not mean there is a gas leak. However, if you smell gas around the boiler, close the gas valve without touching any electrical switches, open the windows, leave the building and call Enerya Antalya's 187 natural gas emergency line from outside.

If your boiler keeps losing or gaining pressure, call Devka Doğalgaz on +90 553 028 82 80. You can also book an on-site visit anywhere in Antalya through our contact page.