With pressure above
minimum, remove Modureg
Lead. Does pressure drop to
minimum?
36
Is minimum pressure
observed at burner at all
times?
Modulating Valve Check
Flow turbine Check
GO TO
CHECK I
YES
YES
YES
YES
NO
YES
YES
NO
NO
NO
NO
Is pressure at burner
always the same?
Is resistance
nominally 125ohms?
Does voltage
go above 6.25V?
Faulty PCB.
Replace
Reconnect X6 and measure
voltage across modulating
valve during operation
Gas valve OK
Does the boiler ignite
at a higher flow rate?
Faulty turbine.
Replace.
Faulty PCB.
Replace
Disconnect the 3 way in-line
connector.
Check that there is 5V DC output
from the PCB at the connector.
Red +5V Black 0V
Faulty modulating valve .
Replace gas valve
Remove X6, measure
resistance between
pins 15 & 16
N
YES
NO
O
Re-connect the 3 way connector
and open a tap to run the turbine.
Check that there is between 1.5 and
4.5 V DC across the green and black
wires/terminals.
With boiler cold, slowly open HW
tap. When flow reaches 3l/min
does boiler ignite? (Flow can be
checked using a measuring jug and
stop watch)
YES
NO
GO TO
CHECK I
HARNESS OK
YES
Faulty turbine.
Replace
Turbine OK
NO
NO
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