F70
FAULT CODE
Glow-worm
Invalid Device Specific Number (DSN)
Medium Severity
Engineer Required
The boiler has an invalid or unrecognised device-specific configuration number. Usually occurs after PCB replacement.
Step-by-Step Fix Guide
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Step 1
This usually only appears after PCB replacement
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Step 2 Engineer only
The engineer who fitted the PCB needs to program the correct DSN using the boiler's configuration menu
Gas Safe Reminder
Work on gas appliances must be carried out by a Gas Safe registered engineer. The steps above cover safe checks a homeowner can perform - any internal component replacement requires a qualified professional. If in doubt, always call an engineer.