Glow-worm is a British heating brand now part of the Vaillant Group. Since its acquisition by Vaillant in 1996, Glow-worm’s boiler range has shared increasing amounts of engineering DNA with the parent brand — which has a significant practical implication: many Glow-worm spare parts are interchangeable with Vaillant components, particularly pump assemblies, gas valves, and fan motors.
This cross-compatibility makes Glow-worm one of the better-supported older brands in terms of parts availability, even as new-install market share has declined.
Key Boiler Ranges
Glow-worm Ultimate
Glow-worm’s current offering — built on Vaillant ecoTEC platform components with Glow-worm-specific casing and controls. The Ultimate Combi 3 uses substantially the same internal components as the Vaillant ecoTEC Plus.
Glow-worm Energy
Widely installed series from the 2010s. The Energy uses Vaillant-derived components — confirming the Vaillant equivalent part number often resolves parts sourcing for the Energy range faster than sourcing direct Glow-worm OEM parts.
Glow-worm Flexicom CX (Legacy)
An older combi range popular in the 2000s. Some electronic components are reaching end-of-production. Call our helpline to confirm availability.
Most-Searched Glow-worm Parts
PCB: PCB failure on Ultimate models presents similarly to Vaillant ecoTEC failure.
Fan Motor Assembly: F9 on Glow-worm Ultimate and Energy indicates fan speed outside the expected range. The fan assembly for Energy models is substantially the same as the Vaillant ecoTEC fan.
Pump Assembly: Glow-worm Energy and Ultimate pump assemblies are Grundfos-based, matching the Vaillant ecoTEC specification.
Gas Valve: Glow-worm F1 (flame loss/failure to ignite) leads investigation to the gas valve after ignition components are confirmed functional.
Pressure Differential Switch: Like the Vaillant F75, Glow-worm boilers can develop pressure switch faults linked to the pump circuit.
Glow-worm Fault Codes
F9 — Fan Fault
The fan has not reached the required speed for the pre-ignition purge, or has lost speed during operation.
Causes:
- Failed fan motor (most common)
- Fan motor capacitor failure
- Blocked flue
- Wiring fault between PCB and fan motor
- Failed air pressure switch
Parts linked to F9: Fan motor assembly, air pressure switch, PCB.
F1 — Flame Failure / Ignition Failure
F1 indicates either failure to establish a flame at ignition, or flame loss during operation.
Causes:
- Gas supply issue — check supply at meter
- Failed ignition electrode
- Failed ignition lead
- Failed gas valve
- Flame rectification failure
Parts linked to F1: Ignition electrode, ignition lead, gas valve, PCB.
F22 — Low System Pressure
Glow-worm Ultimate models share fault code nomenclature with Vaillant ecoTEC. F22 = low system pressure. Same diagnosis and resolution as Vaillant F22.
Vaillant Cross-Compatibility
| Glow-worm Component | Vaillant Equivalent Status |
|---|---|
| Energy 18c/24c/28c pump | Direct equivalent (Vaillant ecoTEC Pro pump) |
| Energy fan assembly | Direct equivalent (Vaillant ecoTEC fan) |
| Ultimate pump | Direct equivalent (Vaillant ecoTEC Plus pump) |
| Ultimate fan | Direct equivalent (Vaillant ecoTEC Plus fan) |
| Pressure differential switch | Direct equivalent |
Call our helpline to confirm cross-compatibility for your specific model: 0330 124 5678.
Compatible Glow-worm Models
Glow-worm Ultimate 18c, 24c, 28c, 30c, 35c (Combi); Ultimate System 18s, 24s, 30s; Energy 18c, 24c, 28c (Combi); Energy System; Flexicom CX (legacy); Compact (legacy regular boiler); Betacom (legacy combi).
Need a Glow-worm Engineer Near You?
Our Recommended Installers have experience with Glow-worm and Vaillant-group boilers:
- HGB Heating Kent — Gas Safe engineers, Kent and Medway
- Boiler Sense — Certified boiler specialists, Kent and South East London