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Reading a fault code

Checked against its sources: Updated

Boiler fault codes are not a shared language: a code means only what the user manual for that exact boiler says it means.12 Baxi's E133, for example, carries two different meanings in two Baxi documents.

Covers
Gas boilers in UK homes, read against six maker families' user manuals
You
Read the display, note the code, look it up in your own user manual, and take only the step that manual gives.
A professional
Any repair, any code your manual sends to an engineer, and any code it doesn't list. For gas, a Gas Safe registered engineer.

1 Why the model matters

Baxi's Compact quick guide lists E133 as a frozen condensate pipe.1 The Baxi Platinum Combi guide lists E133 as an interruption of the gas supply or flame failure.2 Same maker, same characters, different problem, so a chart for another boiler can point you the wrong way. If you aren't sure of the model, start with which boiler you have.

2 What a display can be showing

Six things a display can mean, with an example of each from a user manual
DisplayExampleWhat it tells you
Status codeVaillant S.004: heating mode active, burner operating3Normal running, not a fault
Mode letterIdeal Logic Combi: F with the burner light on means frost mode; F with a digit is a fault5Read the whole display before worrying
Fault codeVaillant F.022: no or too little water, or pressure too low3Something has stopped the boiler
Plain wordsIdeal Logic+: "Low Water Pressure"6The message is the code
Flashing lightBaxi 600 Heat: colour and number of flashes4Count them and note the colour
Number with no meaning givenWorcester Greenstar 4000 uses "fault code 232" only as an example7Quote it to the maker or engineer

3 The maker entries

Each maker has its own entry, giving only what the user manuals read say, with manual, date and page: Worcester Bosch, Vaillant, Baxi, Main and Potterton, Ideal, Glow-worm and Viessmann. A code missing from an entry may still be real.

4 Why the printed lists are short

User documents say themselves that they are partial. Vaillant's 2023 manual says codes outside its table need a competent person.3 Baxi's Compact guide points to the installation and servicing instructions for the complete list.1 Worcester's Greenstar i ErP guide says to contact Worcester if other codes appear.8 Those fuller lists are written for engineers, and meanings from them aren't copied here.

5 What to do with a code

  1. If you smell gas or a carbon monoxide alarm is sounding, leave the display alone and go to if you smell gas or carbon monoxide.
  2. Write down the code and the model. Viessmann's manual says a noted fault number helps the contractor prepare.9
  3. Find the code in your own manual and take only the step printed there.
  4. If that step is a reset, use your model's method, not another boiler's.
  5. If the code returns or isn't listed, call an engineer. Nothing here involves going inside the casing.

Sources

  1. Compact quick guide from Baxi, document 7849761, file dated May 2023 p2, read 3 November 2026.
  2. Platinum Combi guide from Baxi, document 7697821-01, issue 1/18 p8, read 3 November 2026.
  3. Vaillant ecoTEC plus VU/VUW/VUI ..CS/1-5 operating instructions, 0020308119_03, 28.11.2023, Vaillant pp19-20, read 3 November 2026.
  4. 600 Heat guide from Baxi, document 7726861-01, issue 1/19 p23, read 3 November 2026.
  5. Logic Combi guide from Ideal, file dated July 2013; this copy is on InspectApedia's site pp6-7, read 3 November 2026.
  6. Logic+ Combi guide from Ideal, UIN 204979 A07, May 2014; this copy is on the site of Selco, a merchant p18, read 3 November 2026.
  7. Worcester Bosch Greenstar 4000 user instructions, 6 720 891 170 (2020/09) p16, read 3 November 2026.
  8. Worcester Bosch Greenstar i ErP instructions, 6 720 806 946 (2015/03) p24, read 3 November 2026.
  9. Viessmann Vitodens 050-W operating instructions, 6173895 GB 05/2026 p25, read 3 November 2026.