Does flame indicator glow and
flames increase in size to full gas
rate after approx. 2 mins?
Yes
Does burner flame modulate/ go
out when radiator temperature
control is turned left to the
horizontal position at flow
temperature of approx. °50 C?
Yes
Does heating flow pipe
temperature rise?
Go to sheet GYes
Check operation of burner and modulation
Ensure flow and return service
valves are open
No
No
No
Replace electronic board
No
Check operation of boiler in DHW
mode, does flame increase in size
to full rate?
Yes
Check partial load
setting
No
Check diagnostic code D.22
(see page 39) equals 1
No
Go to sheet G
Yes
Check connections and
modulator, replace gas valve if
burner still fails to increase to full
rate
Turn main ON/OFF control to
the "0" position
Yes
Insert a small screwdriver
through the hole in the front of
the diverter valve and hold
blade lightly against spindle
Turn "ON" the main ON/OFF
control
Does spindle move?
Yes
Replace electronic board
Replace diverter valve
No
Sheet F
