A fault code is only useful when it is matched to the correct boiler and manual. This guide is for the current UK Vaillant ecoTEC plus 826 combi boiler: VUW 20/26CS/1-5 (N-GB), article number 0010036015, covered by operating instructions 0020308119_03 dated 28 November 2023.
Older ecoTEC plus 826 boilers can have different controls and filling arrangements. If those details do not match your appliance, use the manual supplied with your boiler or ask a competent heating engineer before pressing buttons or adding water.
What do F.022 and F.028 mean?
On this exact model and manual revision:
- F.022 means there is no or insufficient water in the boiler, or the heating-system pressure is too low.
- F.028 means the boiler did not detect a flame during ignition. After five unsuccessful ignition attempts, it enters fault mode.
Do not remove the boiler casing. Gas, combustion, electrical, flue and internal repair work must be left to a suitably qualified person.
First, record what the boiler is showing
Before trying a permitted homeowner check, note:
- The complete fault code.
- The model name and article number.
- The pressure shown on the display.
- Whether heating and hot water have both stopped.
- Any visible water leak, unusual noise or repeated pressure loss.
A clear photo of the display can help when you arrange a repair.
F.022: check the system pressure
You can read the pressure on the basic display. The manual also allows you to open Main menu → Information → Water pressure to see the current value.
Vaillant recommends at least 1.0 bar. It says to add heating water if the pressure is below 0.8 bar. The manual describes 1.5 bar as a good standard value, but the correct target depends on the height and design of your heating system. Follow the target explained by your installer rather than chasing a generic number from the internet.
If the pressure is too low, F.022 can temporarily stop the boiler. The code should clear automatically once sufficient pressure has been restored.
Only use these filling steps when the arrangement matches
The ecoTEC plus 826 is a combi with integrated hot-water generation. Its current manual shows an integrated filling line with a double non-return valve, a spring clip and two isolation valves.
Only continue if that is the arrangement fitted to your boiler, you can identify it without removing the casing, and your installer has shown you how it works. If it looks different or you are unsure, stop and ask a competent person.
- Open the radiator valves.
- Fit the double non-return valve of the filling line to the cold-water isolation valve and secure it with the spring clip.
- Open the first isolation valve shown in the manual, then slowly open the second valve so water enters the heating system.
- Watch the pressure rise on the display. Stop at the target pressure set for your installation.
- Close the second isolation valve first, then the first valve.
- Remove the filling line from the cold-water isolation valve.
Both isolation valves must be closed and the filling line removed during normal operation.
Do not add water if you cannot positively identify the filling arrangement. Do not exceed the target pressure: the manual warns that excessive pressure can open the expansion relief valve.
Stop and arrange help for a pressure problem when
- water is leaking from the boiler, pipework or a radiator;
- the pressure falls again after topping up;
- the pressure rises unexpectedly or approaches the upper limit;
- the filling valves will not close cleanly;
- F.022 remains after the correct pressure is restored; or
- you are uncertain which valves or filling device apply to your installation.
Repeated pressure loss is not solved by repeatedly adding water. It needs investigation.
F.028: one safe reset attempt
For F.028, Vaillant’s manual tells the user to check that the gas stopcock is open and allows a reset by holding the reset button for more than three seconds.
Only check the normal external gas stopcock if you already know which control it is and what its open position should be. Never open the casing or touch an internal gas component.
If there is no smell of gas, no carbon-monoxide alarm and no other safety concern, make one reset attempt:
- Hold the reset button for more than three seconds.
- Wait for the boiler to complete its start-up sequence.
- If F.028 remains or returns, stop resetting and arrange professional help.
Although the manual states a maximum of three repetitions, this homeowner guide uses a stricter one-attempt boundary. A persistent ignition fault needs diagnosis, not repeated resets.
Gas smell or carbon-monoxide warning
Do not reset the boiler or top up the pressure if you smell gas, a carbon-monoxide alarm sounds, or anyone may be affected by carbon monoxide.
Avoid flames and smoking. Do not operate electrical switches. If possible, open doors and windows, leave the building and keep other people out. From outside, call the National Gas Emergency Number on 0800 111 999. If anyone is seriously unwell, call 999 for urgent medical help.
Frequently asked questions
Is F.022 the same on every Vaillant boiler?
No. This article applies only to the ecoTEC plus 826 VUW 20/26CS/1-5 (N-GB), article 0010036015, covered by manual 0020308119_03. Other models and older revisions can differ.
Will F.022 clear after the pressure is restored?
The manual says the boiler should automatically operate again once a sufficient pressure level is reached. If it does not, or if the pressure drops again, arrange professional help.
Can I leave the filling line connected?
Not on the integrated arrangement shown in this manual. Vaillant says both isolation valves must be closed and the filling line removed during normal operation.
How many times should I reset F.028?
This guide recommends one attempt. If the fault remains or returns, stop and contact a competent person.
Should I open the boiler casing to look for the cause?
No. Internal boiler work is not a homeowner task.
Need help with a persistent Vaillant fault?
Keep the exact code, pressure reading, model/article number and a clear photo of the display. Then visit the MPH Boilers repair page or contact MPH Boilers so the team can confirm service availability and the next step.