Moffat Turbofan G32MS Service Manual Download Page 25

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Revision 6/F3590

Moffat Ltd, February 2005

Burner flame not being sensed

Firstly check phase and neutral at supply for
correct polarisation, as shown on terminal
block label. If incorrect burner will light but
flame sensor will not sense the flame.
The flame sensing electrode requires correct
positioning in the burner flame. Incorrect gas
pressures, types, injector sizes, etc will affect
correct operation of flame sensing system.
Ensure that these are checked and correct
before carrying out further investigation. Also,
an incorrectly earthed/grounded appliance will
cause faults with the flame sensing system.
Always ensure a correct earth/ground

connection on the appliance connection and
supply.
If the flame rod is touching the burner mesh
then there is a short circuit to earth, and this
will cause the ignition control to not sense the
flame correctly. As the relationship of the
flame rod to the burner mesh cannot normally
be seen, this fault would normally be indicated
by a burner that fails to stay alight during
operation, or during an ignition attempt the
sparking continues after the burner is lit. The
flame rod can be adjusted to be clear of the
burner, as per the previous diagram (figure
6.1.1) and section 6.4.11.
Always inspect the connection lead from the
flame rod to the ignition box for deterioration,
bad connections, or insulation breakdown.

Ignition transformer faulty - 110V models
only

It is important to verify correct 110Vac - 24Vac
transformer operation before checking these
24Vac Ignition Control Boxes.
With control panel open check transformer
primary and secondary voltages are correct.

Transformer Primary Winding - 110-120Vac
Lead colours

White - L1 (Phase)

Black - L2 (Neutral)

Check voltage at the black and white lead
connections on control panel. Voltage should

be 110-120Vac. If not, check for wiring or
power supply fault.

Transformer Secondary Winding - 24Vac
Lead colours - yellow and blue

Check voltage at yellow and blue lead

connections on ignition control box. With
thermostat on (calling for heat) voltage should
be 24Vac ± 4Vac across yellow and blue
leads. If not, check transformer thermal
breaker on rear of transformer for trip. If
tripped, reset and recheck operation.
If the transformer cannot be reset, or if
transformer has not tripped out, but secondary
output voltage is incorrect, then transformer is
faulty - replace.

Ignition box faulty - 110V models only

The direct spark ignition control boxes used
on 110V model G32M and G32MS’s are
24Vac type.
To check correct operation open control
panel. With power on, turn thermostat on so
heating indicator on control panel illuminates
(calling for heat).
Correct ignition box operation should result in
ignition box commencing spark at ignition
electrodes and opening gas valve to ignite
burner, then maintain burner ON after

successful ignition.
If no spark is generated or heard, check that
ignition box has correct supply voltage.

(Check voltage across terminal ‘GND’ (black/
green wire) and ‘TH’ (blue wire)). 24Vac ±
4Vac should be measured across these termi-
nals with thermostat on and calling for heat. If
not, check transformer (refer previous).
If voltage correct, but no spark generated,
check ignition box Fault Diagnostic LED

indicator status. The Diagnostic LED is at the
top of the ignition box.
Inspect for Diagnostic Indicator as follows:
- 2 Flashes Indicates that there was a flame

already present when ignition
attempted.

Possible gas valve fault (burner
staying on). Refer to fault

diagnosis - Gas Valve Faulty.

- 3 Flashes Indicates LOCK-OUT condition.

Possible flame rectification rod
short to earth. Refer to fault
diagnosis 6.1.2 - Burner Flame
Not Being Sensed.

If ignition box fault indicator LED does not
identify fault, and voltage correct but no spark
generated, ignition box is faulty - replace.

Figure 6.1.1

FLAME SENSOR

THIS ELECTRODE

MUST BE IN BLUE FLAME

SURFACE COMBUSTION

ORANGE INFRARED BURN