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With pressure above
minimum, remove Modureg
Lead. Does pressure drop to
minimum?
33
Is minimum pressure
observed at burner at all
times?
Modulating Valve Check
Flow Switch Check
GO TO
CHECK I
YES
YES
GO TO
CHECK I
YES
YES
NO
NO
HARNESS OK
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
Remove
X6
Close all taps to set no
domestic flow
Faulty flow switch.
Replace
Faulty flow switch.
Replace
Is short circuit observed
at
X6 pins 1 & 2
Is open circuit observed
at X6 pins 1 & 2?
Open a tap fully to set
domestic flow
Flow Switch OK
Faulty modulating valve .
Replace gas valve
Remove X6, measure
resistance between
pins 15 & 16
N
YES
NO