Glow-worm Swiftflow 100 Fault codes & diagnostics

7 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Combi Gas 1992-1999 Discontinued
GC Numbers 47-313-0747-313-08
Download the Glow-worm Swiftflow 100 manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

This boiler uses LED flash patterns

Count the flashes in one repeating group before the pause. That number is your fault code. Do not reset until you have noted it. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
7 High
Versions & GC numbers

Which version do you have?

The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.

GC number Appliance (register name) Produced
47-313-07 Swiftflow 100 SIT valve 1992–1999
47-313-08 Swiftflow 100 Honeywell valve 1992–1999
Just want the most common Glow-worm Swiftflow 100 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 7 documented codes

Tap any card for details

LED / flash-pattern codes
Red light (flashing)

Your boiler has encountered an internal error and needs a simple restart to try and clear the fault.

High DIY-safe £90-280

What to check first

  1. Locate the electrical spur switch or plug for the boiler
  2. Turn the power off for approximately 30 seconds
  3. Turn the power back on to see if the flashing light stops and the boiler restarts

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Ignition Electrode
  • Overheat Thermostat
Full explanation for Red light (flashing)
Red light flashes

Your boiler has entered a safety lockout mode and has stopped running to protect its internal components.

High DIY-safe £100-280

What to check first

  1. Locate the boiler's electrical power switch (fused spur) on the wall nearby.
  2. Switch the power off for approximately 10 seconds.
  3. Switch the power back on and wait to see if the red light clears and the boiler fires up.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)
Full explanation for Red light flashes
Digital codes
Fuse 1

Your boiler has stopped working because a protective electrical fuse on the main internal computer has blown.

High Engineer only £120-250

Parts commonly replaced

  • T1.6A fuse
  • Main control board (PCB)
Full explanation for Fuse 1
Fuse 2

The main electrical protection component for your boiler's internal computer has failed, which has completely shut down the system.

High Engineer only £120-200

Parts commonly replaced

  • T 630mA fuse
  • Main control PCB
Full explanation for Fuse 2
Red Light

Your boiler has stopped working because there is not enough water pressure in the central heating system.

High DIY-safe £0-120

What to check first

  1. Locate the silver filling loop (flexible hose) underneath or near the boiler.
  2. Slowly open the one or two taps on the loop until you hear water flowing.
  3. Watch the pressure gauge until it reaches between 1 and 1.5 bar, then close the taps tightly.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve
Full explanation for Red Light
red lockout neon

Your boiler has stopped working for safety reasons and needs to be reset to try and fire up again.

High DIY-safe £100-350

What to check first

  1. Locate the reset switch on the control panel
  2. Press and release the reset switch
  3. Wait at least 15 seconds for the boiler to attempt to restart

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame sensing probe
Full explanation for red lockout neon
Red lockout neon (lit)

Your boiler has shut itself down for safety because it either got too hot or failed to light the gas properly.

High DIY-safe £100-£280

What to check first

  1. Locate the reset button (often marked with a flame symbol or 'R') on the control panel
  2. Press and hold the reset button for several seconds and wait for the boiler to restart
  3. Check that your gas pre-pay meter has credit and that other gas appliances like your hob are working

Parts commonly replaced

  • Overheat thermostat
  • Ignition electrode
  • Gas valve
  • Printed Circuit Board (PCB)
Full explanation for Red lockout neon (lit)
Status & diagnostic codes

3 operating states & engineer diagnostics

Not faults — these are normal operating states. Tap to expand.

Green Light Status Your boiler is working normally and currently providing heating or hot water as requested. Orange 'Mains' light Status Your boiler is receiving electrical power, but if the light is off, there may be a problem with the electricity supply or the internal circuit board. Orange Light Status Your boiler is receiving electrical power and is currently switched on or ready to operate.