Vaillant boilers such as the ecoTEC and ecoFIT show codes starting with F or S. An F code (for example F.28) is a fault — the boiler has stopped. An S code is a status message that simply tells you what the boiler is doing at that moment, such as heating or waiting; it isn’t a fault. If you see an S code you don’t recognise, look it up in your user manual.
📊 Common Vaillant Fault Codes
| Code | What it means | What to do |
|---|---|---|
| F.22 | Water pressure too low, or not enough water in the boiler | ✅ Top up to 1–1.5 bar, then reset |
| F.28 | No flame detected when the boiler tried to light | ✅ Check gas supply, reset once |
| F.29 | Flame lost during operation and the boiler couldn’t relight | ✅ Check gas supply and condensate pipe, reset once |
| F.24 | Temperature rising too quickly — often a circulation problem | Check pressure, then call an engineer |
| F.75 | Pressure didn’t change as expected when the pump started — pump or pressure sensor | Check pressure, then call an engineer |
| F.61 | Gas valve control fault | Call an engineer |
Seeing a different F code? Check your user manual, or call us with the full code and the model name on the front of the boiler.
💧 F.22 — Low Water Pressure
- Turn the boiler off and let the system cool.
- Top up the pressure with the filling loop, following the steps in your boiler’s user manual, until the gauge reads about 1–1.5 bar.
- Close the filling valves fully, turn the boiler back on and reset it.
If you’re not comfortable doing it, or the pressure keeps dropping, call an engineer — a pressure that keeps falling means a leak or a faulty part. More help: boiler pressure low.
🔥 F.28 and F.29 — Flame Faults
F.28 means the boiler couldn’t light. F.29 means the flame went out while running and the boiler couldn’t relight.
- Do your other gas appliances, such as the hob, work? If not, the problem is the gas supply, not the boiler.
- On a prepayment meter? Check it has credit.
- In freezing weather, check the condensate pipe outside isn’t frozen. Thaw it with a hot water bottle or warm (never boiling) water, only where you can reach safely from the ground.
- Then press the reset button once.
If the code comes back, stop resetting and call a Gas Safe engineer. The cause is usually a part such as the ignition electrode, flame sensor or gas valve.
⚙️ F.75 and F.24 — Circulation Problems
Both point to water not moving round the system as it should — low pressure, air in the system, a sticking pump or a faulty pressure sensor. Check the pressure gauge first and top up if it’s low. If the code returns after that, it needs an engineer.
💷 Vaillant Repair Costs in London
| Repair | Rough price |
|---|---|
| Low pressure or condensate fix | £80 – £150 |
| Sensor, thermostat or ignition part | £100 – £250 |
| Diverter valve, fan or pump | £150 – £350 |
| Gas valve or circuit board (PCB) | £200 – £550 |
| Heat exchanger | £300 – £700 |
Rough guide for London, parts and labour. The exact price depends on your boiler and the part. Our engineer gives you a fixed price after seeing the boiler, before any work starts. No VAT added.
Boiler still under its Vaillant guarantee? Contact Vaillant first, as they deal with guarantee repairs. Old boiler that keeps breaking down? See repair or replace your boiler.
🏆 Vaillant Repairs with FE Maintenance
- Gas Safe registered, fully insured — every engineer works directly for FE Maintenance, no subcontractors
- Fixed price agreed before any work starts, no VAT added
- Emergency call-outs Monday to Friday, 8am–8pm, from £99 — see emergency gas engineer
- Yearly boiler service from £80 to catch faults early
We cover North, West and Central London, plus Potters Bar and Hatfield. Call 020 8445 1303 or ask for a quote.
General guidance based on Vaillant’s published fault code information and manual tables, as of October 2026. Codes vary between models — your boiler’s user manual is the final word.
Frequently Asked Questions
Vaillant Still Showing a Fault?
A Gas Safe engineer from FE Maintenance can find the cause and fix it, with a fixed price agreed before any work starts.
info@femaintenance.com · 171 Crescent Road, Barnet EN4 9RN