I have had a read-around here and cannot find quite the same symptom, but then Potterton are popular here so it may have been lost in the noise.
temperature it seems that it lights periodically to maintain the temperature as expected, however one of these relights seem to fail.
In the fault condition, the boiler is out, fan is no longer turning, the red led is flashing and the pump is running. This condition will last indefinitley. Pressing reset while the HW is off just stops the pump, if HW is on the fan turns, pump runs and after a few secs, gas, spark and normaillity again. (Changing the pump speed also stops the pump).
The frequency of occurence has built up over the last 2 years.
I thought it was the pump, since the pump body was hotter than all the pipework around it, and speed 2 seemed to do nothing, so I swapped in a Wilo Gold 60 for the old Myson CP53.
However the fault persists.
Unit is 5 yr old, fitted by builder, serviced once professionally (he condemmed installation, builder fixed it same day) since then I have checked the combustion chamber for soot etc, completely clean so I figured best left well alone.
So before I disassemble it completely to diagnose I thought I would see if this is a common problem.
Chris