I'm not familiar with these. On Goldline Controls we just hold the diagnostic button for 3 sec and check cell light goes away.
Do we hold the cubby select button for 3 seconds? or is it longer?
This probably is an old unit. I've pressed the select button for 3 secs and light stops flashing but then a minute later the light starts flashing again. cell is clean and I've inspected it all. just need to reset this light.