Brymen EEVblog BM235 User Manual page 14

 Faulty Photocell
 Temperature over 165
For gas flames (Flame Rod):
 Ignition interference (A flame signal current difference with the ignition both on and
off greater than 0.5  A indicates the presence of ignition interference)
 Insufficient ground (must be at least 4 times the detector area)
 Flame lifting off burner head (ground), or not continuously in contact with the flame
rod
 Temperature in excess of 600
short to ground.
o F (74 o C) at photocell
o o
F (316 C) at the flame electrode insulator causing