Boilers fault codes by brand
Every domestic boiler sold in the UK since 2005 is a condensing boiler with a control board that reports faults as a code. Find your manufacturer below, then your code, and you will get the same five answers every time: what it means, whether it is safe, what causes it, what you can try, and what a repair costs.
Brands
Pick your manufacturer to see every code we cover.
Most looked-up boiler codes
Across every brand in this category.
- EA 227Worcester BoschThe boiler tried to light and never detected a flame, so it has shut the gas off and locked out. This is the most common Worcester fault code.Stop — call an engineer
- F.22VaillantThe boiler has shut down because there is not enough water in the system. Pressure has dropped below roughly 0.5 bar and it will not fire until you top it up.Get it checked
- F.75VaillantThe boiler cannot detect a rise in pressure when the pump starts, so it has locked out. Usually a failed pressure sensor or a pump that is not moving water.Get it checked
- F1IdealSystem pressure has dropped below the minimum the boiler will run at. Topping it back up to 1.2 bar usually clears it straight away.Get it checked
- E01AlphaThe appliance tried to light and could not confirm a flame, so it has locked out. In winter a frozen condensate pipe is the most likely reason.Get it checked
- F.28VaillantThe boiler tried to light and failed three times in a row, so it has shut the gas off and locked out. Do not keep resetting it.Stop — call an engineer
- CE 207Worcester BoschSystem water pressure has dropped too low for the boiler to run safely. Topping the system back up to 1.2 bar usually clears it in five minutes.Get it checked
- 501AristonNo flame was detected during ignition and the appliance has locked out. Check the gas supply and the condensate pipe before booking anyone.Get it checked
- A01VokèraThe burner failed to light and the appliance has locked out. Check the gas supply and, in cold weather, the condensate pipe before calling anyone.Get it checked
- E10AlphaSystem water pressure has fallen too low for the appliance to fire. Top the system back up to 1.2 bar and it will restart.Usually simple to fix
- L2IdealThe boiler failed to detect a flame during ignition and has locked out on the gas valve. Do not keep resetting it.Stop — call an engineer
- 108AristonThe heating circuit does not contain enough water to run safely. Refill through the filling loop to about 1.2 bar and the code clears.Usually simple to fix
- E119BaxiSystem pressure has fallen below the level the boiler will operate at. Refilling to 1.2 bar and resetting usually clears it in a few minutes.Get it checked
- F.28Glow-wormIgnition was unsuccessful at start-up and the boiler has locked out. Check the gas and the condensate pipe before calling anyone.Get it checked
- A04VokèraSystem water pressure is below the minimum the appliance will run at. Topping the system back up to 1.2 bar normally clears it straight away.Usually simple to fix
- E133BaxiThe boiler failed to establish a flame and has locked out on the gas valve. Do not reset it more than twice.Stop — call an engineer
- E133PottertonIgnition failed and the appliance has locked out. On a Promax the condensate run is the first thing to check in cold weather.Get it checked
- A01FerroliThe burner failed to light and the appliance has locked out. Ferroli list a blocked siphon as a cause, which is worth checking early.Get it checked
- E119PottertonThe appliance has stopped because system pressure is too low. Refilling to 1.2 bar clears it, but on an old system the reason it fell matters more.Get it checked
- F.29VaillantThe boiler lit correctly and then lost the flame while it was running. It has shut the gas off and locked out, and it needs an engineer.Stop — call an engineer
Symptoms
No code on the display? Start from what it is doing.
Boiler keeps losing pressure
A sealed heating system does not use water, so a gauge that keeps falling means water is escaping somewhere. Here is how to work out where.Boiler making a banging or kettling noise
A boiler that bangs, rumbles or sounds like a kettle boiling is telling you that water is not moving through it properly. It is worth acting on rather than living with.No heating and no hot water at all
Before assuming the boiler has failed, there are four things worth checking that account for a large share of these call-outs and cost nothing to rule out.No hot water but the heating still works
When heating works and hot water does not, the fault is almost always in the part of the boiler that switches between the two rather than in the boiler itself.
How boilers fault codes work
A boiler fault code is not a diagnosis. It is the control board telling you which of its safety checks failed, and the same code can have four or five different underlying causes. That is why "F1 means low pressure" is true but not useful on its own — the question that matters is why the pressure fell.
Codes fall into a handful of families that repeat across every manufacturer. Pressure faults mean the sealed system has lost water. Ignition faults mean the boiler tried to light and could not confirm a flame. Overheat faults almost always mean water is not circulating rather than that the burner is running too hard. Fan and flue faults mean the boiler cannot verify that combustion products are being cleared. Once you know which family you are in, the diagnosis follows.
Two rules are worth knowing before you touch anything. First, a lockout is a safety device doing its job, and resetting it repeatedly to force the boiler to run is how expensive components get destroyed. Two resets is the sensible limit for any code. Second, gas work is legally restricted to Gas Safe registered engineers in the United Kingdom. Checking a pressure gauge, opening a filling loop, or thawing a condensate pipe are all things you can do. Removing the case is not.
Pressure
The sealed system has lost water and the boiler will not fire without it.
Ignition and gas
The boiler tried to light and could not confirm a flame.
Overheat and circulation
Heat is being produced faster than the water can carry it away.
Fan and flue
The boiler cannot verify that combustion products are being cleared.
Sensors and electronics
A sensor or the control board is reporting a value that cannot be right.
Guides
How to repressurise a boiler
The five-minute job that resolves more no-heating calls than any other. Here is how to do it properly, and how to tell when topping up is the wrong answer.What to do when your condensate pipe freezes
The single most common winter boiler fault, and one of the few you can genuinely fix yourself in fifteen minutes with a kettle and some patience.Boiler fault codes explained: what they actually tell you
Codes look like diagnoses and are not. Understanding which family a code belongs to turns a meaningless number into a genuinely useful starting point.