A fault code is the boiler telling you which safety check it failed. It is not a full diagnosis, but it narrows the possibilities enormously, which is why the first thing we ask on the phone is what the display says.
Below are the code families we see most often on the makes we install and service every week: Vaillant, Worcester Bosch and Ideal. Codes vary between models, so always cross check against your own manual. Nothing here asks you to remove a cover.
Vaillant: F.22, F.28, F.75 and F.29
F.22 is low water pressure, and it is the most common Vaillant code we are called about. Check the gauge, and if pressure is genuinely low the cause is a leak or an expansion vessel rather than the boiler being thirsty.
F.28 is a failed ignition, F.29 is a flame lost during operation, and F.75 points at the pressure sensor or pump combination on many ecoTEC models. F.28 and F.29 both sit firmly in Gas Safe territory because they involve the gas train and combustion.
Worcester Bosch: EA, E9, C6 and F0
EA is generally no flame detected, which can be as simple as a gas supply issue or as involved as an electrode or gas valve fault. E9 usually indicates overheat, often caused by poor circulation, a sticking pump or sludge, which is a system health problem rather than purely a boiler one.
C6 relates to the fan and F0 is an internal fault. Both are engineer work. If a Worcester unit is showing overheat codes repeatedly, we would want to look at the system water quality and the filter as well as the boiler.
Ideal: L2, F1, F2 and C2
L2 is ignition lockout, F1 is low water pressure on many Logic models, F2 is flame loss and C2 relates to the fan or pump depending on the range. As with the other makes, the pressure codes are the only family with a genuine homeowner action attached.
- Pressure codes: check the gauge, top up carefully if your manual permits, then get repeat losses diagnosed.
- Ignition and flame codes: one reset at most, then book a Gas Safe engineer.
- Overheat codes: usually circulation, so expect a conversation about flushing and filtration.
- Fan, sensor and internal codes: always an engineer, and often a stocked part.
What we do with the code before we arrive
Knowing the make, model and code lets us bring the likely part rather than making two trips. On a Vaillant we are a Vaillant Advanced Installer, so we are working with equipment we know intimately and can advise properly on whether a repair or a replacement makes better financial sense given the boiler's age and warranty status.
If the boiler is under a manufacturer warranty, tell us. There are situations where the correct advice is to use the warranty route, and we will say so rather than charging for work you already have covered.
Frequently asked questions
- Is a fault code the same as a diagnosis?
- No. A code says which check failed. For example a flame loss code can be gas supply, ignition components, condensate blockage or a flue issue. It narrows the list, which is why it is genuinely useful, but the diagnosis still happens at the boiler.
- Can I clear a fault code myself?
- You can attempt one reset. If the code returns, the boiler is protecting itself and needs an engineer. Never repeatedly reset a boiler showing ignition, flame or overheat codes.
- Which makes do you work on?
- We install and service Vaillant, Worcester Bosch and Ideal as our main makes, and we are a Vaillant Advanced Installer, which allows extended warranties of up to 12 years on qualifying installations. We service and repair most other domestic makes too.
- My boiler is old and keeps coding. Repair or replace?
- We give you the numbers rather than a sales pitch: the cost of this repair, the likely next failure, the age and efficiency of the unit, and what a replacement would cost. Plenty of older boilers are worth repairing, and we will tell you when that is the case.
Tell us the code and we will bring the part
Send us the make, model and exact code from the display. It is the fastest way to a first time fix instead of a return visit.