Remedy
Note: Combustion case off can case this fault.
1. Refer to blocking errors(s) that lead to this locking error. Check the fault history on the appliance.
2. Possibly the purging of the gas pipe is incomplete.
3. It could also indicate a wide variety of issues such as pipework undersized or gas pressure dropping off, incorrectly routed condens drains, incorrectly sited flues, incorrectly wired etc.