Fault finding and diagnosis
Greenstar Danesmoor External
ErP+
and External System
ErP+
6720821725 (2018/04)40
8.2 Heating and hot water
These fault finding charts are provided to assist competent and suitably qualified engineers to locate and rectify faults. Whilst every effort has been
taken to ensure the information given is correct and complete we cannot guarantee that every eventuality has been covered.
Worcester, Bosch Group cannot be held responsible for costs incurred by persons not deemed to be competent.
Measure all 230V tests between Neutral (N) and the pin, wire or terminal specified.
6720809437-44.1Wo
Start
No heating/hot water
Is the demand light
illuminated?
Follow the control box
fault nding chart to
locate fault.
Is the burner lockout
light illuminated?
No
Is there 230V on pin 2 of
the control thermostat?
(the brown wire)
Is there 230V on the L
connection on the burner
control box?
No
Locate fault between the
control thermostat and
the burner. Repair
fault/replace lead.
UNDER NO
CIRCUMSTANCES MUST
AN APPLIANCE BE LEFT
OPERATING WITH ANY
CONTROL LINKED OUT OR
OVER RIDDEN.
No
Yes Yes
Yes
Replace the control
thermostat.
No
Replace the burner
control box.
Yes
Yes
Set the service switch to
Boiler mode
No
Is the service switch set to
Boiler mode?
No demand to the boiler.
Check external supply and
wiring. Rectify the fault.
Lack of system water circulation.
Check the pump, valves and system.
Rectify the fault.
Is the boiler hot?
No
Yes
Reset the thermostat and investigate
cause of overheat. If the thermostat
will not reset replace the thermostat.
Is the ue or boiler
overheat thermostat
tripped out?
No
Yes
Is there 230V on the
orange wire to the ue
overheat thermostat?
Yes
Replace the boiler
overheat thermostat.
No
Is there 230V on the
brown wire from the ue
overheat thermostat?
Yes
Replace the ue
overheat thermostat.
No
Is there 230V on pin 2
(brown wire) on the
burner socket?
Yes
Replace the high
limit thermostat.
No
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