A Vaillant boiler shows an F code when it has spotted a problem and shut down to protect itself. The most common ones in winter are F.22 (low water pressure), F.28 (failed ignition), F.29 (flame lost) and F.75 (pump or pressure sensor). Some can be cleared with a simple pressure top-up or one reset, but repeat codes need a Gas Safe registered engineer. We carry out boiler service and repairs on Vaillant boilers across Harlow and Bishop’s Stortford, and these are the codes we hear about most once the cold arrives.
How Vaillant fault codes work
Most Vaillant ecoTEC boilers show a code on the display, starting with F and followed by a number. The code tells you which safety check the boiler has failed. Exact meanings can vary slightly between models, so always check the user manual for yours.
A fault code is not always a broken part. Sometimes it’s a simple supply or pressure issue. The code is the starting point for working out which.
F.22: low water pressure
F.22 means the boiler has detected too little water pressure in the heating system. It’s one of the most common codes and often follows bleeding radiators or a small leak.
What you can safely do:
- Check the pressure gauge. Many systems sit around 1 to 1.5 bar when cold, but check your manual
- If it’s low, top it up using the filling loop as described in the manual
- Reset the boiler once
If the pressure keeps dropping, there’s likely a leak or a faulty pressure relief valve. That needs an engineer.
F.28: ignition failure on start-up
F.28 means the boiler tried to light but didn’t detect a flame. Common causes include:
- No gas reaching the boiler, for example a prepayment meter that has run out
- A faulty ignition electrode or ignition lead
- A gas valve problem
- A blocked condensate pipe, which on some models can stop the boiler and show as an ignition fault
Check other gas appliances are working and that your meter has credit, then reset once. If it returns, call an engineer.
F.29: flame lost during operation
F.29 is similar to F.28, but the flame went out while the boiler was running rather than on start-up. It can point to an interrupted gas supply, a flue problem or a faulty sensor. In cold weather, a frozen condensate pipe is also worth checking. Our post on why a boiler keeps shutting down covers the wider causes.
F.75: pump or pressure sensor fault
F.75 means the boiler didn’t detect the expected rise in pressure when the pump started. That can be caused by low system pressure, air in the system, a sticking pump or a faulty pressure sensor.
Check the pressure first, and bleed any radiators that are cold at the top. If the code comes back, the pump or sensor needs testing by an engineer.
When to stop and call an engineer
Leave it to a Gas Safe registered engineer if:
- The same code returns after one reset
- You need to open the boiler casing for any reason
- There’s water leaking from the boiler
- You notice soot, staining or a smell of fumes
If you smell gas, turn off the supply at the meter if it’s safe to do so, open the windows and call the National Gas Emergency Service on 0800 111 999.
Vaillant boiler faults in Chelmsford, Harlow and across Essex
Homes around Chelmsford and Harlow include plenty of post-war houses and newer estates where combi boilers are tucked into kitchen cupboards, with condensate pipes running outside. Those external pipes are the ones most likely to freeze in a hard frost. In older homes, sludge in the system can also make pump and pressure faults more likely.
Frequently asked questions
How do I reset a Vaillant boiler?
Most Vaillant boilers have a reset button on the front panel, marked with a flame symbol or the word reset. Press it once and wait a minute or two. If the boiler fires up and the code clears, keep an eye on it. If the same code comes back, don’t keep resetting, as the fault needs finding properly.
Can a frozen condensate pipe cause a Vaillant fault code?
Yes. If the condensate pipe freezes, waste water backs up and the boiler shuts down. Depending on the model, it can show as an ignition or flame fault. Pouring warm, not boiling, water over the frozen section of pipe outside is a safe homeowner fix. If you’re unsure where the pipe runs, call an engineer.
Is it safe to keep using my boiler with a fault code?
If the boiler has locked out, it won’t run until the fault is cleared. If it restarts after one reset and runs normally, it’s usually fine to keep using while you monitor it. Repeated codes, leaks or any smell of gas or fumes mean you should stop and get it checked.
Vaillant boiler showing a fault code?
If your Vaillant boiler keeps showing the same code, give us a call on 01279 771981 or drop us a message and we’ll send an engineer to find the fault and get it fixed.