HP Officejet Pro 8720 error message "Supply System Problem"

[Piers3]

This error message appeared in the middle of printing yesterday evening.  It suggests I should change all three cartridges i.e. C, M and Y.  Given that it is highly unlikely that all three cartidges ran out at the same time this seems a very expensive test at around £75.00.  I've tried turning the machine off and back on a few minutes later as well as reseating all of the cartridges.  Any suggestions for an alternative?

[Rainbow23]

Hi @Piers3,

Welcome to HP Support Community. 
Thank you for posting your query. I will be glad to help you.

I see that you are getting an error message “supply system problem” on your Officejet Pro 8720 Printer.

I suggest that you follow the steps listed below to reset the unit: 
1. Turn the printer on if it is not already on.
2. With the printer turned on, disconnect the power cord from the rear of the printer.
3. Unplug the power cord from the wall outlet.
4. Wait for 60 seconds.
5. Plug the power cord back into the wall outlet.
NOTE: HP recommends connecting the printer power cord directly to the wall outlet.
6. Reconnect the power cord to the rear of the printer.
7. Turn on the printer if it does not automatically turn on. 

You may also check the steps in the document. 

Let me know if this helps.
Take care and have a great day ahead.

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