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Vaillant boiler fault codes
Common Vaillant codes for ecoTEC plus, ecoTEC pro, ecoTEC sustain and ecoFIT pure boilers, what they mean and what to do.
Vaillant boilers show an F code, usually written with a dot, such as F.28. The display may also show a spanner symbol. Here are the codes we see most often in South London homes.
| Code | What it means | What to do |
|---|---|---|
| F.22 | Low water pressure. The boiler has stopped because there is not enough water in the heating system. | Check the pressure gauge. If it is below 1 bar, top it up to about 1 to 1.5 bar using the filling loop, as your manual shows. If it keeps dropping, book a repair: there is a leak or a faulty part. You may be able to fix this |
| F.28 | Ignition failure. The boiler tried to light at start-up and could not. | Check other gas appliances work and your meter has credit. In freezing weather, check the condensate pipe outside is not frozen. Reset once. If it comes back, book a repair. Engineer needed if it returns |
| F.29 | Flame lost while running. | Check your gas supply as above, then reset once. Repeated F.29 usually needs an engineer to check the gas pressure, flue and electrodes. Engineer needed if it returns |
| F.27 | False flame. The boiler sensed a flame when there should not be one. | Do not keep resetting. This needs a Gas Safe engineer to check the gas valve and flame sensor. Engineer needed if it returns |
| F.75 | Pressure sensor or pump fault. The boiler did not detect a pressure change when the pump started. | Check the pressure is above 1 bar. If it is, the pump or pressure sensor needs checking by an engineer. Engineer needed if it returns |
| F.61 | Gas valve control fault. | Not a DIY fix. Book a repair visit. Engineer needed if it returns |
| F.20 | Overheat safety cut-out. The boiler got too hot and shut down to protect itself. | Often low water flow, air or sludge in the system. Check the pressure, then book a repair if it returns. Engineer needed if it returns |
| F.00 / F.01 | Temperature sensor fault on the flow (F.00) or return (F.01) pipe. | Usually a faulty sensor or loose connection. Book a repair visit. Engineer needed if it returns |
Codes and their meanings can vary between models and software versions, so check your boiler’s manual too. Never open the boiler casing yourself.
How to top up the pressure
Low pressure is the most common cause of a Vaillant lockout. With the boiler cold, open the filling loop valves slowly until the gauge reads about 1 to 1.5 bar, then close them fully. Your manual shows where the filling loop is on your model. Read our full guide.
When to book an engineer
- The same code comes back after one reset
- The pressure keeps dropping after you top it up
- You see a false flame, flue or gas valve code
- There is water leaking from the boiler
Vaillant questions
What does F.22 mean on a Vaillant boiler?
Low water pressure. The boiler has stopped because there is not enough water in the heating system. Check the pressure gauge. If it is below 1 bar, top it up to about 1 to 1.5 bar using the filling loop, as your manual shows. If it keeps dropping, book a repair: there is a leak or a faulty part.
How do I reset a Vaillant boiler?
Most models have a reset button or a dial position marked reset. Press or turn it once, and wait a few minutes for the boiler to try again. Check your manual for your model. If the code returns, do not keep resetting it.
Do you repair Vaillant boilers?
Yes. Our Gas Safe engineers repair Vaillant boilers across South London. A repair visit is £90 including the first hour.
Other makes: Worcester Bosch, Ideal, Baxi.