Search my own database of fault, diagnostic and status codes to aid in fault identification.
Check everything is plugged in correctly, especially if you have external components such as a condensate pump. In rare occasions, this can be caused by a blocking signal on the burner blocking port when wired in.
Top up the appliance with water.
Pump lame, shaft disconnected, blocked, valves closed?
This is likely that the PCB is starting to break down and detecting a flame when not present.
Check gas supply before going any further.
Boiler was in operation, but the flame went out and the boiler was unable to re-establish the flame after repeated attempts.
Possibly an external controls issue or internal circuit board. The eBus is the communication between all the digital controls and can be sometimes caused with polarity issues.
This can be caused by the gas valve or PCB, more likely the PCB on this one, check gas valve resistance at 50-54 Ohms (Roughly).
Most likely the PCB, however this can be thrown if the gas valve is letting-by and a such, a local tightness test is advised.
New PCB
Check NTCs and harness, but likely to be PCB.
Either the PCB is starting to break down, or there is an external heat source influencing the PCB and it's getting too hot.
It's likely this is a PCB issue. However this is a fault that regularly appears if there is any damp within the PCB housing or on the PCB.
Check condensate, otherwise emissions test and adjust air/gas ratio before swapping out the gas valve.
PCB has likely been replaced with a reconditioned one from a slightly different model and the DSN code needs a reset, click for more info.
Flow NTC is not adjusting with known temperature increase.
Temperature difference is too great between flow and return.
Reading out at an invalid value, replace.
Reading out at the wrong range or not providing a stable reading. Replace.
Pump flow not detected on pump initialisation. Blocked water pressure sensor or defective is the normal cause, however pump must be checked.
Check the thermal fuse on the top of the exchanger, it it's failed, new boiler. Be warned, the connection between the thermal fuse and loom can be delicate on some models so the loom must be checked.
If you have Vaillant controls, check wiring and configuration setup to the VRxx box.
With low temp issues, this can indicate a faulty NTC or PCB as the boiler holds off, adjusting from auto to fixed kw output can sometimes help.
