Bosch CONDENS 5000W - 7 Fault Finding and Diagnosis; Fault Finding

Fault finding and diagnosis
Bosch Condens 5000W – 6 720 646 195 (2018/10)
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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.
This fault finding system assumes that the boiler has been operating
normally until the time of failure (i.e. not a first installation error).
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.
Basic checks
• Ensure that there is 230V power supply and the polarity is correct to
the appliance.
• Ensure that the appliance settings and functionality is correct.
• Ensure the CH/DHW programmer/timer is functioning.
• Ensure the room thermostat is functioning.
• Ensure the cylinder thermostat (if fitted) is functioning.
• Ensure the cold water mains is turned on?
• Ensure the primary system has adequate pressure/system content
for the system type.
• Ensure there is gas to the appliance?
– Are other gas appliances working, gas cooker/hob for example?
– Has the credit run out on the gas pre-payment meter?
NOTICE:
On completion of the Service/Fault-Finding task which has required
the breaking and remaking of electrical connections, check:
▶ Earth continuity,
▶ Short circuit check,
▶ Polarity,
▶ Resistance to earth.
Blue light
indication
Lockout reset
button
Fault Possible solution/check
OFF OFF No power at control
board
▶ Check:
– Permanent mains supply to the boiler
– Fuse F1 - 2.5A or Fuse F3 - 0.5A
– Transformer (primary coil below 60, both secondary coil below 60.
▶ Otherwise replace control board
ON OFF Boiler not operating
during central heating
demand
▶ Check:
– Live demand at ST10-L
R
(from external controls, room thermostat/timer)
– Fascia mounted (if fitted)
– CH control knob is not in winter position ( )
▶ Otherwise replace control board
Boiler operating
without live demand at
ST10-L
R
(from
external controls,
room thermostat/
timer)
Some older thermostats (containing capacitors) may give a low voltage return at
ST10-L
R
when the thermostat contacts are open.
▶ Check that there is no permanent live at ST10-L
R
from another source.
– Rectify external equipment providing voltage when there should be none
during a no demand period.
Boiler not operating
during hot water
demand (CH ok)
▶ Check:
– Live demand at ST10-L
R
(from external controls, cylinder thermostat/timer)
– Fascia mounted (if fitted)
– CH control knob is not in winter position ( )
▶ Check (if “optional integral diverter valve” is fitted)
– Diverter valve
– Diverter valve motor
▶ Otherwise replace control board
Boiler not operating
during any demand.
▶ Check fan:
▶ Otherwise replace control board