28
e
the temperature at the primary thermistor has
dropped 6
°
C below the set-point.
NOTES
The timer delay can be de-activated by the
insertion of a ‘jumper’ on the PCB or by isolating
the appliance from the electrical supply for 30
seconds.
Any DHW request will always have priority over
the heating request.
When the request for heating has been satisfied,
the appliance pump and fan may continue to
circulate to dissipate any residual heat within the
appliance.
7.2.6
DHW MODE
With the selector switch in the Heating & HW
position, or HW only position, and a DHW outlet
is opened, the appliance will operate in the HW
mode. The valve actuator will motor to the HW
position (if a heating request was active) and the
pump and fan will be active. The operation of the
fan causes the analogue pressure switch (PAD)
to deliver a signal voltage to the control PCB. If
the signal voltage is sufficient a slow ignition
sequence is enabled, whereby the current
supplied to the gas valve modulating coil is
progressively increased from minimum to
maximum over a period of 8-seconds. During this
period the ignition electrode sparks continuously
even if the burner has ignited.
NOTE
If the spark/sensing electrode does not sense
ignition the appliance will then go to lockout.
Ignition is sensed by the electronic circuitry to
ensure flame stability at the burner. Once
successful ignition has been achieved, the
electronic circuitry modulates the appliance
output in order to achieve the DHW set-point (the
position of the DHW temperature selector) as
measured at the secondary thermistor.
When the set-point has been reached, the
appliance will begin the modulation phase
whereby the fan and gas valve will continuously
modulate to maintain the set-point.
If the temperature continues to rise and exceeds
the set-point by 5
°
C, the burner will shut down
until the temperature drops to set-point + 4
°
C,
whereby a new ignition sequence will be enabled.
When the request for heating has been satisfied,
the appliance fan may continue to operate to
dissipate any residual heat from within the
appliance.
7.3
CHECKING AND ADJUSTING BURNER PRES-
SURE (see fig. 19)
Although the burner pressure is factory set, it is
necessary to check it during servicing or if the
gas valve has been removed.
Isolate the appliance from the electrical supply
and attach a suitable manometer to the gas valve
outlet test nipple.
7.3.1
SETTING THE MAXIMUM BURNER PRES-
SURE (see fig. 44)
Light the boiler as described in 5.7 and compare
the reading on the manometer with the value
described in 2.3. If adjustment is required, remove
the protective cap from the gas valve modulating
coil assembly and turn the outer (10mm) nut
clockwise to increase, or counter-clockwise to
decrease the burner pressure.
NOTE
Always check and/or adjust the minimum and
maximum gas pressures whilst the appliance is
in the HW only mode. Ensure a DHW outlet
(preferably the bath) is fully open, and that the
HW temperature selector is at maximum.
7.3.2
SETTING THE MIMIMUM BURNER PRESSURE
(see fig. 45)
Once the maximum burner pressure has been
checked and/or adjusted, remove one of the grey
wires from the modulating coil. Compare the
reading on the manometer with the value
described in 2.3. If adjustment is required, turn
the inner (red) crosshead screw clockwise to
increase, or counter-clockwise to decrease the
burner pressure, whilst ensuring that the outer
(10mm) nut does not move. When checking and/
or adjustment has been completed, isolate the
appliance from the electrical supply, replace the
protective cap, refit the grey wire to the
modulating coil, remove the manometer and
tighten the outlet test nipple.
IMPORTANT, A GAS SOUNDNESS CHECK
MUST BE CARRIED OUT.
7.4
COMBUSTION ANALYSIS TEST
A combustion analysis check can easily be
carried out on the appliance via the test points
located on the top of the appliance, however you
must check that the burner pressures are set
correctly (see 7.3).
●
Insert the flue gas analyser probe into the right
hand test point (see fig 46).
●
Locate and remove the protective cap that
conceals the ‘CO mode’ butto (see fig. 46).
Fig. 44
Fig. 45
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