Fault Finding And Diagnosis - Bosch CONDENS 5000W User, Installation And Servicing Instructions

AU/NZ
7

Fault finding and diagnosis

7.1 Fault finding
This fault finding information is for guidance
only. Robert Bosch cannot be held
responsible for costs incurred by incorrectly
diagnosed faults.
The electronic control system for this boiler
incorporates a blue central indicator. This normally
confirms the permanent mains supply but, by flashing at
different rates during a fault, provides a guide to the
cause as listed.
Blue light Lockout
indication reset button
Off Off
On Off
Tab. 28
Fault Possible solution/check
No power at Permanent mains supply to boiler.
control board
Fuse F1 - 2.5A or Fuse F3 - 0.5A.
Transformer (primary coil below 60 Ω, both secondary coil below
10 Ω).
Otherwise replace control board.
Boiler not Live demand at ST10-L
operating
Fascia mounted timer (if fitted)
during central
CH knob in winter position
heating demand
Control board
Boiler operating Some older thermostats (containing capacitors) may give a low
without live voltage return at ST10-L
demand at open.
ST10-L (from
R
Check that there is no permanent live at ST10-L
external room
source.
thermostat
timer)
Boiler not Fan
operating
Control board
during any
demand.
Fault finding and diagnosis | 61
This fault finding system assumes that the boiler has
been operating normally until the time of failure (i.e. not
a first installation error).
Preliminary electrical system checks are the first
electrical checks to be carried out during a fault-finding
procedure. On completion of the Service/Fault-Finding
task which has required the breaking and remaking of
electrical connections, check:
(a) Earth continuity,
(b) Short circuit check,
(c) Polarity and
(d) Resistance to earth.
(from external room thermostat/timer)
R
when the thermostat contacts are
R
from another
R
6 720 646 195a (2010/11)