Boiler Fault Codes Explained
Worcester, Vaillant, Ideal, Baxi and Glow-worm fault codes in plain English
If your boiler is showing a fault code, the first thing is to slow down and work out what the boiler is trying to tell you. Boiler fault codes usually point toward pressure, ignition, circulation, overheating, sensors, frozen condensate pipes, or gas-side faults.
Some codes are simple homeowner checks. Others need a Gas Safe engineer because the fault sits inside the boiler casing, around ignition parts, the fan, PCB, flue, gas valve, pump or internal sensors.
MPS Heating & Plumbing LTD helps homeowners across Croydon, Thornton Heath, Addiscombe, Norbury, South Croydon, West Croydon, Selhurst and East Croydon with Worcester boiler fault codes, Vaillant boiler fault codes, Ideal boiler fault codes, Baxi boiler fault codes and Glow-worm boiler fault codes. Gas Safe Registered — ID 662170, with a 5.0 Google rating from 60 reviews.
If your boiler has locked out, keeps flashing the same code, or will not fire after one reset, call 0203 576 6769 and we’ll talk through the safest next step before you book anything.
Before you panic about a boiler fault code
A fault code does not always mean the boiler is finished. It means the boiler has detected something outside its normal working range and has either warned you or shut itself down to protect the appliance.
For example, a Vaillant F75 fault code is often described as a pressure sensor issue, but what is really happening is this: the boiler is checking whether water actually moves when the pump starts. You may still see pressure on the gauge, but the boiler cannot detect the pressure change it expects.
In winter, we often see Croydon homes with Worcester EA 227, Ideal L2, Baxi E133 or Glow-worm F28 style ignition faults where the real cause is not always the gas valve. Sometimes it is a frozen condensate pipe, poor ignition, low gas supply, or a fault that has only shown itself once the heating is under heavy demand.
If the fault appeared after missed checks, pressure problems, banging noises or repeated resets, a proper boiler servicing and fault check can help find the cause rather than just clearing the code for a day.
Quick boiler fault code table
| Brand / Code | Plain English meaning |
|---|---|
| Worcester EA 227 | Ignition or flame detection problem. In cold weather, also check for a frozen condensate pipe before assuming a major part has failed. |
| Vaillant F75 | The boiler cannot detect the pressure change it expects when the pump starts. Often linked to pump, sensor, sludge or circulation problems. |
| Ideal L2 | Ignition lockout. The boiler has tried to light but has not safely established a flame. |
| Baxi E119 | Low pressure. The heating system may need repressurising, but repeated pressure loss points to another issue. |
| Glow-worm F22 | Low water pressure or circulation issue. Check the gauge first, but do not keep topping it up if pressure keeps dropping. |
Safe checks before calling an engineer
You can check the pressure gauge, reset the boiler once, look for an obvious frozen condensate pipe outside, check thermostat batteries, and make sure the gas meter or prepayment meter has credit.
You can also note the exact code, when it appears, and whether you still have heating or hot water. That helps a lot. A photo of the display is useful too.
Do not remove the boiler casing. Do not touch gas valves, fans, ignition electrodes, PCBs, flues, burners or internal wiring. That is Gas Safe work.
If the code keeps coming back after one reset, stop resetting it. Repeated resets can hide the original fault pattern and make diagnosis harder.
Safe To Check
Pressure gauge, thermostat batteries, frozen external condensate pipe, gas meter credit, timer settings, and one reset if the boiler manual says it is safe.
Do Not Attempt
Opening the casing, working on the gas valve, fan, PCB, burner, electrodes, flue, combustion parts or internal wiring. Those checks need a Gas Safe engineer.
When It Is Urgent
If there is leaking water, burning smell, repeated lockout, no heat in winter, gas smell, or the boiler will not stay on, get advice rather than forcing resets.
Real engineer insight: fault codes are clues, not the full diagnosis
A code tells you where the boiler thinks the problem is. It does not always tell you why that problem happened.
We often see Vaillant F75 faults on older systems without magnetic filters, where sludge and magnetite have built up and affected circulation. We see Worcester EA 227 faults in winter where the condensate pipe has frozen outside. We see Ideal L2 codes where the boiler has failed to ignite, but the reason still needs checking properly.
That is why “just reset it” is not always good advice. If the same code comes back, the boiler is warning you for a reason.
If you are in Croydon, Thornton Heath, Norbury or East Croydon and the same fault code keeps returning, call 0203 576 6769 and we’ll help you work out whether it sounds like a simple check or an engineer visit.
Worcester Bosch boiler fault codes
Worcester boiler fault codes and Worcester Bosch boiler fault codes often show as letters and numbers on the display. Some people also search for Worcester boiler fault codes PDF, but for a homeowner the useful bit is usually simple: what does the code mean, can you check anything safely, and when should you stop?
| Worcester code | What it usually means |
|---|---|
| EA 227 | Ignition or flame detection fault. You may notice no heating, no hot water, clicking, or repeated lockout. In winter, check whether the condensate pipe outside is frozen. |
| C6 | Fan issue. This is not a DIY repair. Fan and flue-related checks need a Gas Safe engineer. |
| E9 | Overheating or safety temperature issue. This can link to circulation, blocked flow, pump faults, sludge or sensor problems. |
| A1 | Low water or circulation issue. Check pressure first, but repeated faults need diagnosis. |
| D1 | Sensor or flow-related fault depending on model. Best checked properly if it returns after reset. |
Vaillant boiler fault codes
Vaillant boiler fault codes are common searches because the codes can feel alarming. Vaillant F75, F22, F28 and F29 are especially common because they often affect heat, hot water, pressure or ignition.
| Vaillant code | What homeowners usually notice |
|---|---|
| F75 | The boiler is checking whether water moves when the pump starts. This can be pump-related, sensor-related, or caused by sludge and poor circulation. |
| F22 | Low water pressure or dry-fire protection. Check the pressure gauge. If pressure keeps dropping, there may be a leak or another pressure fault. |
| F28 | Ignition failure. The boiler has tried to light but cannot establish flame. Gas supply, ignition parts, condensate issues or gas-side faults may be involved. |
| F29 | Flame loss after ignition. The boiler lights, then loses flame. This needs proper checking if it repeats. |
If your Vaillant boiler fault code is linked with pressure dropping, see our guide on boiler pressure loss and repeated top-ups.
Ideal boiler fault codes
Ideal boiler fault codes are usually clear once you know the pattern. The Ideal boiler L2 fault code is one of the big ones because it usually means ignition lockout.
| Ideal code | Plain English explanation |
|---|---|
| L2 | Ignition lockout. The boiler has not safely lit. You may have no heating or hot water, and the boiler may click or attempt to start. |
| F1 | Low water pressure. The boiler may not fire until pressure is corrected, but pressure dropping again needs investigation. |
| F2 | Flame loss or ignition-related issue depending on the model. Stop resetting if it keeps returning. |
| L1 | Overheat or circulation issue. Can be linked to pump, air, blockage, sludge or flow problems. |
| F3 | Fan fault. This is not a homeowner repair. Fan and flue checks need a Gas Safe engineer. |
If your Ideal code appears with no hot water but heating still works, it may be worth reading our page on hot water failing while the heating still runs.
Baxi boiler fault codes
Baxi boiler fault codes often point toward pressure, ignition or overheating. E119 and E133 are two of the most common homeowner searches because they normally stop the boiler working properly.
| Baxi code | What it normally points to |
|---|---|
| E119 | Low pressure. Check the gauge and repressurise only if you are confident. If pressure keeps falling, the cause needs finding. |
| E133 | Ignition failure. In winter, frozen condensate pipes can sometimes be involved, but gas-side issues also need checking. |
| E110 | Overheat fault. Often linked to circulation, pump, blockage, air or sludge issues. |
| E125 | Circulation fault. The boiler may be struggling to move heat around the system properly. |
If the boiler fault appears alongside banging, knocking or rumbling, read our guide on boiler noises linked to circulation problems.
Glow-worm boiler fault codes
Glow-worm boiler fault codes can look similar to Vaillant codes on some models because the brands are related. F22, F28 and F9 are common codes homeowners search when the boiler stops firing or pressure looks wrong.
| Glow-worm code | Likely meaning |
|---|---|
| F22 | Low pressure or water circulation issue. Check the gauge first. Repeated pressure loss needs proper diagnosis. |
| F28 | Ignition fault. The boiler cannot safely light. Gas supply, ignition parts, condensate or flame detection issues may be involved. |
| F9 | Pressure sensor or circulation-related issue depending on model. Can be linked to system water quality or sensor failure. |
If the code appears after water near the boiler, read our advice on leaking boilers and when water becomes urgent.
Winter boiler fault codes
Cold weather changes everything. A boiler that ran fine in October can suddenly fail on a freezing January morning when the system is under more demand.
The biggest winter issue is the frozen condensate pipe. If the white plastic pipe runs outside, it can freeze and cause the boiler to lock out. This can show up as ignition faults, gurgling, failed starts or repeated resets.
Pressure can also drop in winter because the heating is running longer, small leaks show themselves, and older systems expand and contract more often. Gas meters and prepayment meters can also cause problems if the supply is interrupted.
If you are unsure, do not start opening the boiler. Check what is safe from outside the appliance, then call for advice.
No Guesswork
We look at the code, symptoms, pressure, heating behaviour, hot water behaviour, reset history, condensate pipe, gas supply and visible signs before recommending repairs.
Straight Advice
If it is a simple frozen pipe, low pressure or thermostat issue, we will say so. If it needs proper boiler repair diagnosis, we explain why before work starts.
Local Experience
MPS Heating & Plumbing LTD works with Worcester Bosch, Vaillant, Ideal, Baxi and Glow-worm boilers across Croydon and South London. Gas Safe Registered — ID 662170.
Typical boiler fault repair costs
Repair cost depends on the real cause, not just the fault code. A pressure sensor may be around £100–£180. An ignition electrode can often fall around £90–£160. A pump replacement may be around £250–£450. PCB work can be much higher, often around £350–£600 depending on the boiler and part.
If a boiler is 12+ years old and needs a PCB plus a pump, replacement may make more financial sense. If it is a simple sensor, pressure issue, condensate blockage or ignition part, repair can still be the sensible route.
What Customers Have Said
“Ansar came round at short notice to diagnose and identify the issue with my faulty boiler. He went above and beyond.”
— Marcello Carnevale“Great work! Really quick response and turnaround to identify and fix the problem.”
— Michael Arko-Adjei“He talked us through what was happening, why and how long it would take. He then delivered on time.”
— Ellis Cain-JonesFault code keeps coming back?
If the same boiler fault code keeps returning, do not keep clearing it and hoping it disappears. The boiler is showing that code because something is not right.
Call MPS Heating & Plumbing LTD and we will ask the brand, the exact code, whether heating or hot water still works, what the pressure reads, and whether the issue started during cold weather.
Boiler Fault Codes FAQs
Can I reset my boiler safely?
Usually one reset is fine if the boiler manual says so. If the same fault code comes back, stop resetting it. Repeated resets can hide the original fault pattern and may delay proper diagnosis.
Why does my boiler fault code keep coming back?
Because the boiler is detecting the same problem again. It could be low pressure, ignition failure, overheating, frozen condensate, poor circulation, a sensor fault, fan issue, or another internal fault.
Is low boiler pressure dangerous?
Low pressure is not usually dangerous by itself, but it can stop the boiler firing. If pressure keeps dropping after topping up, there may be a leak, PRV issue, expansion vessel fault or hidden system problem. See our guides on boilers losing pressure and pressure dropping overnight.
Why does my boiler fail during cold weather?
Cold weather can freeze the condensate pipe, increase heating demand, expose weak circulation, and make existing pressure or ignition issues show up more often.
How much do boiler repairs cost in London?
Small sensor or ignition parts may be around £90–£180, pumps can often be £250–£450, and PCB work can be £350–£600 depending on the boiler. The exact cost depends on diagnosis, brand, part availability and labour.