Boiler
E19
The E19 error code on a Glow-worm boiler indicates a fan or air pressure fault — specifically, the boiler’s air pressure switch is detecting incorrect flue or airflow conditions. This is a safety lockout, meaning your boiler has shut itself down and will not restart until the underlying issue is resolved.
What does this error mean?
Your Glow-worm boiler continuously monitors the airflow through its flue using a component called the air pressure switch (or differential pressure switch). When this switch fails to confirm that air is moving correctly — either before or during a heating cycle — the boiler triggers the E19 lockout to prevent unsafe combustion. In plain terms: the boiler thinks something is wrong with how exhaust gases are being expelled, and it’s protecting your home by refusing to fire.
Est. repair cost
£80–£350 depending on faulty component (pressure switch vs. fan); new boiler £1,800–£3,000 installed
🔍 Likely causes
🛠️ Step-by-step fix
Check the external flue terminal: Go outside and visually inspect the boiler’s flue outlet (usually a white plastic vent on an external wall or roof). Clear any visible blockages such as leaves, cobwebs, or debris. Do not use a ladder unless you are confident doing so safely.
Check for a frozen condensate pipe: In cold weather, locate the white or grey plastic pipe that exits your boiler and runs outside. If it feels solid or looks iced over, thaw it gently by pouring warm (not boiling) water over the frozen section, or wrap it with a warm wet cloth.
Reset the boiler: Once you’ve checked for obvious blockages, press and hold the reset button on your Glow-worm boiler (usually marked with a flame symbol or labelled ‘Reset’) for 3–5 seconds. Allow the boiler to complete its start-up sequence and monitor for 10 minutes.
Check the pressure switch hoses (visual only): If you’re comfortable locating the boiler’s internal components with the casing closed, listen for any unusual rattling or hissing sounds during start-up that may suggest a loose connection — but do NOT remove the boiler casing yourself.
Do not attempt further DIY: Any fault beyond a blocked flue terminal or frozen condensate pipe involves gas components, electrical wiring, or sealed parts. Attempting to replace the fan, pressure switch, or PCB yourself is illegal without Gas Safe registration and potentially dangerous. Stop here and call a professional.
📞 When to call a professional
If the boiler fails to restart after clearing an obvious external blockage or thawing the condensate pipe, call a Gas Safe registered engineer immediately — do not keep attempting resets, as repeated lockouts can indicate a worsening fault. Tell the engineer: ‘My Glow-worm boiler is showing an E19 error code — I believe it’s a fan or air pressure switch fault.’ This will help them arrive prepared with the correct parts.
⚖️ Repair or replace?
A fan replacement on a Glow-worm boiler typically costs £150–£350 including labour; an air pressure switch is cheaper at £80–£180 all-in. If your boiler is over 10–12 years old and facing a fan or PCB fault, replacement becomes financially competitive — a new boiler costs £1,800–£3,000 installed. For boilers under 8 years old in otherwise good condition, repair is almost always the right call.