D.M. Procida wrote:

The "no flame" neon indicator is flashing (suggests flame failure or
condensate drain blockage).

The condensate drain is not blocked.

However, I seem to have fixed it by removing the condensation tank, and
drying it, particularly near where the sensor wire is connected to it. I
think that it was damp, and sufficient current was leaking to trigger
the fault indication.

Daniele