Knowledge Base


Tips for troubleshooting PLC pump sets



When trouble shooting older PLC based fuel oil supply systems without a HMI, or alarm lights there is an easy way to narrow the search.

Steps to Troubleshoot

Two good tools to remember to use is the job specific wiring diagram and the status indication lights on each module.

All Preferred PLC based logic controllers are based on a normally closed contact and using the wiring diagram and the lights on the modules it is easy to tell if a contact is open or closed causing the condition.

(Please note that for all Fuel oil supply systems that have flow switches provided, these are normally closed when the fuel is not flowing and will open when the pump is on and fuel is flowing. this is the only circumstance where a open contact is normal).


An example would be when you have an alarm for a lose of fuel flow in automatic, you take the wiring diagram and identify where the pump on contact is and you identify which module and which light corresponds with this contact and you see that the light is out, but you also notice that the off contact and the high level contact and the pump set leak contact lights are also out.

Based on the logic and the wiring diagram and these lights you would start your troubleshooting at the pump set leak contact  as under a normal operation this contact along with the high level and the pump off contacts should be closed not open.