Low boiler pressure or a code on the display

Start with the pressure gauge

Your cv-ketel (the Dutch word for the boiler) has a pressure gauge or a digital reading on its display. It shows the water pressure in the heating circuit, in bar. Without enough pressure, most boilers stop to protect themselves.

Read it when the heating has been off for a while. Intergas says the pressure should be between 1 and 2 bar with the system cold. Its boilers flash the reading if it drops below 0.5 bar while running. Other makes give their own figure in the user manual, so check yours.

The reading rises a little once the water is hot. What matters is where it sits when cold, and whether it stays there.

How to top up with the vulkraan

Topping up (bijvullen) means letting drinking water into the heating circuit through the vulkraan (filling valve). On some boilers this is a small tap underneath; others need a vulslang (filling hose) from a nearby tap. Your manual shows which. You never need to take the casing off.

Intergas describes these steps for its boilers:

1. Let the system cool, so you read the cold pressure.
2. Fill the hose with water first, so there is no air in it.
3. Connect it to the filling point under the boiler.
4. Open the drinking-water tap, then the filling valve, slowly.
5. Watch the gauge and stop once it is between 1 and 2 bar.
6. Close the filling valve first, then the tap.

Then bleed the radiators, because topping up brings air in, and check the pressure again. My guide to radiators that won’t heat up walks you through bleeding.

Pressure that keeps dropping

Topping up once after bleeding is normal. Every few weeks is not. Intergas says to tell your installer if you have to top up several times a year, because there may be a leak. Milieu Centraal says the same: a lot of pressure loss can point to leaking pipes.

Before you call, look for:

• drips, or a green or white crust, at radiator valves and bleed screws
• damp patches on ceilings or floors under the pipe runs
• water on the floor under the boiler
• a pipe from the boiler to a drain or outside wall that drips after the heating has run

That last pipe usually comes from the overstortventiel (safety valve). If it drips, the pressure has been getting too high, often because the expansievat (expansion vessel) has lost its charge. That is not a DIY repair. A weeping radiator valve is something I sort out as part of radiator work.

Pressure too high

If the gauge is above the range while the system is cold, it has usually been overfilled. Let a little water out through a radiator bleed screw, with a cloth and a cup underneath, until the reading is back in range.

If the pressure only climbs when the heating runs and falls back as it cools, the expansion vessel is the usual suspect. Don’t keep draining and refilling: every refill adds fresh water and air to the system. Get it checked instead.

Reading a fault code on an Intergas

When an Intergas boiler detects a problem, the fault light flashes red and a code appears on the temperature display. Intergas explains these codes on its page about faults:

• Code 1: the temperature in the boiler is too high. Open the radiator valves, bleed the system and check the pressure is between 1 and 2 bar. If it keeps happening, call an installer.
• Code 4: no flame signal. Check that the gas tap to the boiler is open. If it was closed, open it and press reset. If it was open and the code stays, call an installer.
• Code 5: a poor flame signal. Intergas says to call an installer.
• Code 6: a fault detecting the flame. Again, call an installer.

Missed the code? Switch the boiler off with the off button, then press the service button. The last fault code flashes on the display. For a code that isn’t on the list, Intergas points you to the manual or your installer.

Other makes

I work on Vaillant, Intergas, Remeha, ATAG and Nefit-Bosch. Each maker uses its own codes, so the same number means something else on another boiler. The maker’s own list is the one to trust. The make and model are on the type plate.

• Vaillant publishes an official list of its fault codes.
• Remeha points you to the fault list in the user manual and its online fault finder.
• Nefit-Bosch refers you to the user manual and your installer.
• ATAG: look the code up in the manual for your model. ATAG says your installer is the first point of contact for a fault.

Reset once, then stop

A reset is for after you’ve dealt with the obvious cause: pressure back in range, gas tap open, radiator valves open. Press the reset button once, as your manual describes.

If the same code comes back, stop. A boiler that locks out again has a fault inside, and more resets won’t clear it. Vaillant, for example, marks most of its codes as a job for a certified installer.

Never take the casing off or try a repair inside. Anything behind the casing is work for a professional, never a DIY job.

When to call me

If the pressure keeps dropping or a code keeps coming back, send me a message on WhatsApp with a photo of the display, the pressure reading, the make and model, and your postcode. Boiler repair explains how a repair visit works.

My rate is €114.95 incl. BTW per hour, with no call-out charge. Materials are extra, and I explain the cost before I start. I work by appointment, 08:00-16:00, seven days a week. I don’t run a 24-hour breakdown service.

Heading into autumn? The winter boiler check lists what to look at, and a boiler service at the right interval catches a lot of this early.

If you smell gas, leave the property and call 0800 9009 from outside. If a CO alarm goes off or you suspect carbon monoxide, get everyone outside and call 112.