Repair
No hot water, cold radiators and a flashing code on the display: your boiler has locked out. The code may look cryptic, but it tells you exactly where the problem lies. In this article you'll learn what the most common codes mean, what you can safely try yourself and when it's better to call an engineer straight away.
What is an error code exactly?
Modern boilers monitor themselves continuously. If the boiler notices something unusual — low water pressure, a failed ignition, a sensor reporting strange values — it shuts down as a precaution and shows a code on the display. The boiler is then "locked out": it will only restart once the cause has been resolved and the fault has been reset.
Every manufacturer uses its own codes. Vaillant codes start with an F, Nefit/Bosch uses combinations of digits and letters, and Intergas works with single digits or flashing lights. Your boiler's manual (or the sticker inside the front panel) contains the full list.
What to check yourself first
Before calling an engineer, run through these four checks. They resolve a good share of fault messages:
- Check the water pressure. Is the gauge or display below 1 bar? Top up the system to 1.5-2 bar. Air in the system? Read our step-by-step guide on bleeding your boiler.
- Make sure the gas valve is open. After renovation work or moving house, the gas valve is sometimes (half) closed. Also check whether other gas appliances are working.
- Check the thermostat. Dead batteries or a lost connection between thermostat and boiler can look like a boiler fault, but are easy to fix.
- Reset the boiler once. Press the reset button (often a flame symbol or "reset") and wait a few minutes. Does the boiler start normally and does the code stay away? Then it was a one-off.
Common error codes by brand
Below are the codes our engineers encounter most often in practice. Codes vary by model — when in doubt, always consult your boiler's manual.
| Brand | Code | Meaning | What can you do yourself? |
|---|---|---|---|
| Vaillant | F.22 | Water pressure too low | Top up to 1.5–2 bar and reset |
| Vaillant | F.28 | Ignition failed | Check the gas valve, reset once |
| Vaillant | F.75 | Pressure sensor or pump faulty | Call an engineer |
| Nefit / Bosch | 6A | Burner won't ignite | Check the gas valve, reset once |
| Nefit / Bosch | EA | No flame detected | In winter: thaw a frozen condensate pipe, then reset |
| Intergas | 1 | Overheating | Open radiator valves; if the code returns, call an engineer |
| Intergas | 4 | No flame signal | Check the gas valve, reset once |
| Intergas | 8 | Fan fault | Call an engineer |
Low water pressure: the most common fault message
By far the majority of fault messages are about low water pressure. That's usually harmless: bleeding radiators or small temperature fluctuations make the pressure drop slowly. Topping up once or twice a year is normal. But if you have to top up every few weeks, water is leaking somewhere or the expansion vessel is worn. Have that investigated before it causes consequential damage.
Does the error code keep coming back?
A code that keeps returning after a reset points to a genuine defect: a worn ignition electrode, a fouled heat exchanger, a broken fan or sensor. That's work for an engineer with proper measuring equipment. Working on a gas appliance yourself is dangerous and in many cases not even permitted.
Good to know: many recurring faults can be prevented with periodic maintenance. During a service, the engineer cleans the burner and heat exchanger and spots wear before it leads to a lockout.
Key takeaways
- Note down the error code and check yourself first: water pressure, gas valve, thermostat
- Reset the boiler once at most — don't keep clearing a recurring fault
- Low water pressure is the most common cause: top up to 1.5-2 bar
- Smell gas? Close the gas valve, ventilate and call immediately
Immediate help with a breakdown
Can't solve it with the steps above, or does the error code keep returning? Our engineers are available 24/7 in Amsterdam and the surrounding area and are often on site the same day for emergencies. See our repair service or call +31 85 050 1600 directly.
