Pool and Spa
Questions about Pool Repair? Ask an Expert Online.
when was your filter last cleaned? If the pump has been off and then goes on and the heaters fires and then goes off, you may have a dirty filter that is affecting the pressure switch. The reason is the flow into the filter builds dirt back onto the media and cuts flow. It falls off with the pump going off and momentarily increases flow.
If the filter was recently cleaned, you need to address the pressure switch in the presence of good flow. LO is an indicator of no flow.
I would look into the pressure switch if the pumps are all running good and you have not altered valves.