Complete Boiler Fault Code Reference Guide: All Major Brands

Complete Boiler Fault Code Reference Guide

When your boiler stops working, the fault code on the display is your first clue to what's wrong. Here's a complete reference guide to fault codes for all the major boiler brands we work on at Sanju's Heating.

Vaillant Fault Codes

Vaillant boilers use 'F' codes. Here are the most common:

| Code | Meaning | Can you fix it? | |------|---------|----------------| | F.20 | Overheat safety switch-off | No — call an engineer | | F.22 | Low water pressure | Yes — repressurise to 1.5 bar | | F.23 | Temperature spread too large | Try bleeding radiators | | F.24 | Temperature increase too fast | Check pressure, bleed radiators | | F.28 | Ignition failure | Check gas supply, reset | | F.29 | Flame lost during operation | Check gas supply | | F.54 | Gas supply fault | Check gas valves | | F.61 | Gas valve control fault | No — call an engineer | | F.75 | Pump / pressure sensor fault | Check pressure, bleed radiators |

Full guide: Vaillant Fault Codes

Worcester Bosch Fault Codes

Worcester Bosch uses alphanumeric, 3-digit, and 4-digit codes depending on the model:

| Code | Meaning | Can you fix it? | |------|---------|----------------| | EA | Flame not detected / gone out | Check gas, condensate pipe | | E9 | Safety temperature limiter tripped | Check pressure, bleed radiators | | A1 | Pump has run dry / stalled | Check pressure | | C6 | Fan speed too low or stopped | No — call an engineer | | 1017 | Water pressure too low | Yes — repressurise | | 2927 | Flame failed during burner operation | Check gas supply |

Full guide: Worcester Bosch Fault Codes

Ideal Fault Codes

Ideal boilers use 'F' and 'L' codes:

| Code | Meaning | Can you fix it? | |------|---------|----------------| | F1 | Low water pressure | Yes — repressurise to 1.5 bar | | F2 | Flame loss during operation | Check gas supply | | F3 | Fan fault | No — call an engineer | | L2 | Ignition lockout | Check gas, reset | | L9 | Overheating | Check pressure, bleed radiators |

Full guide: Ideal Fault Codes

Baxi Fault Codes

Baxi uses 'E' codes:

| Code | Meaning | Can you fix it? | |------|---------|----------------| | E118 | Water pressure low | Yes — repressurise to 1.5 bar | | E128 | Frequent loss of flame | Check gas supply | | E133 | Gas supply fault | Check gas, reset | | E160 | Fan fault | No — call an engineer |

Full guide: Baxi Fault Codes

Glow-worm Fault Codes

Glow-worm (part of the Vaillant group) uses similar 'F' codes:

| Code | Meaning | Can you fix it? | |------|---------|----------------| | F.20 | Safety thermal cut-out operated | Check pressure, bleed radiators | | F.22 | Low water pressure | Yes — repressurise to 1.5 bar | | F.28 | Ignition unsuccessful | Check gas supply, reset | | F.75 | Pressure sensor fault | Check pressure, bleed radiators |

Full guide: Glow-worm Fault Codes

General advice for any fault code

1. Check the pressure — Should be 1.0–1.5 bar. Low pressure is the most common fixable fault.
2. Check the gas supply — Make sure other gas appliances work.
3. Check the condensate pipe — In cold weather, check for a frozen pipe.
4. Try resetting — After checking the above, try resetting the boiler.
5. Don't keep resetting — If the fault returns, there's an underlying problem.
6. Call a Gas Safe engineer — For any fault you can't fix, or if you're unsure.

Need help with your boiler?

Sanju's Heating covers Newbury, Basingstoke and Reading. We're Gas Safe registered and can diagnose and repair all major boiler brands with transparent pricing.

Call us on 01635 74 50 40 or book online at sanjusheating.co.uk/book