boilers
Vaillant Boiler Fault Codes: What They Mean and How to Fix Them
Vaillant Boiler Fault Codes in London
Vaillant boilers display fault codes on the digital display when something goes wrong. Understanding what each code means helps you decide whether it is a simple fix or whether you need a Gas Safe engineer.
F22 — Low Water Pressure
F22 is the most common Vaillant fault code in London. It means the boiler pressure has dropped below the safe minimum (typically 0.5 bar). London's aging pipework and expansion vessels are common causes.
Self-fix possible: Yes, if the pressure is simply low. Repressurise the boiler using the filling loop until the gauge reads 1.0–1.5 bar. If the pressure drops again within days, there is a system leak requiring an engineer.
F28 / F29 — Ignition Fault
F28 and F29 indicate the boiler attempted to ignite but failed. Common causes include a faulty ignition electrode, gas supply interruption, or a stuck gas valve.
Self-fix: Check your gas supply (other gas appliances working?). If gas is on, reset the boiler once. If F28/F29 returns, call a Gas Safe engineer — do not attempt to repair gas components yourself.
F75 — Pressure Sensor or Pump Fault
F75 indicates the boiler cannot detect a pressure change when the pump starts, suggesting a faulty pressure sensor or failed pump. This is one of the most common repairs on Vaillant ecoTEC boilers over 5 years old.
Self-fix: Not possible. Requires a Gas Safe engineer to replace the pressure sensor or pump.
F83 — Flow Temperature Sensor
F83 means the flow temperature sensor is not reading correctly. Often caused by a faulty NTC thermistor or wiring fault.
Self-fix: Not possible. Engineer required to test and replace sensor.
Frequently asked questions
Can I reset my Vaillant boiler myself?
Yes — most Vaillant fault codes can be reset by pressing the reset button (flame symbol). The boiler will attempt to restart. If the same code reappears, the underlying fault needs repair by a Gas Safe engineer.
Why does my Vaillant boiler keep losing pressure in London?
Pressure loss usually indicates either a system leak (micro-leak on a radiator valve, pipe joint or heat exchanger) or a failing expansion vessel. London properties with older pipework are particularly prone to micro-leaks at compression fittings.
How long does a Vaillant boiler repair take in London?
Simple repairs (pressure sensor, electrode, sensor replacement) typically take 1–2 hours. Gas valve or PCB replacement may take longer if parts need ordering. Our engineers carry common Vaillant parts to complete most repairs same day.