BoilerFaultCodes Running lamp flashing
The boiler has a built-in delay timer.
Malvern 20/26 Fault codes & diagnostics
5 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Regular Natural Gas 5.8-7.6 kW 2000 onwards Discontinued
GC Number 41-555-18
Download the Malvern 20/26 manual
PDF
Versions & GC numbers
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 →
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 |
|---|---|---|
| 41-555-18 | twentytwentysix | 2000–present |
Appliance names and production years are taken from the UK Product Characteristics Database (the SAP/SEDBUK register). Where a GC number is also printed in this model's own manufacturer manual, both sources were checked to agree.
Just want the most common Malvern 20/26 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes
All 5 documented codes
Tap any card for details
LED / flash-pattern codes
Digital codes
Boiler automatically stops functioning
Blocked condensate pipework (e.g., frozen condensate pipework) detected by the syphon trap blocked drain device.
Lockout lamp illuminating (Flue Thermostat)
The flue thermostat will trip if the flue exceeds a pre-set temperature.
Lockout lamp illuminating (Overheat Thermostat)
The overheat thermostat will trip if the water flow rate is insufficient.
Phase reversed neon (behind the knob) lighting
L and N supply are reversed; the boiler will not progress beyond pilot ignition.