Thermo Products GMC-85, OMC-70 service manual Module GMC or ignition transformer OMC

All installations and services must be performed by qualified service personnel.

After pre-purge, does the ignition control (GMC) or the oil primary (OMC) produce a spark at the ignition electrodes?

No

Is there 24 VAC across the power terminals of the ignition control module (GMC) or 120 VAC across the ignition transformer (OMC)?

Yes

No

On the GMC,has the burner motor centrifugal switch closed? If 120 VAC is measured across the switch, replace the burner motor. Else, replace thermostat. On the OMC, try resetting the oil primary control by depressing the RESET button. Check cad cell function. If all else fails, replace the oil primary.

Yes

Check wiring to the electrodes and ignition control module fuse (GMC) or the ignition transformer and the electrodes (OMC). Also, check ignition electrode gap. Reset if necessary. Replace electrodes, ignition control

module (GMC) or ignition transformer (OMC).

While ignition electrodes are sparking does fuel valve open?

Yes

No

Is there 24 VAC (GMC) across

"MV" terminals on ignition

control module during ignition attempt. Does the oil solenoid valve have 120 VAC across it during the ignition attempt (OMC)?

Yes

Check wiring to fuel valve.

If valve does not open,

replace fuel valve.

No

On the GMC, reset the module by interrupting power to system for more than one second. If this does not work, replace ignition control module. On the OMC, try resetting the oil primary control by depressing the RESET button. If this does not work, replace the oil primary.

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