1. Either the optional flow switch or the optional low water cutoff is not making.
2. Blown fuse.
1. Check boiler pump operation on a call for heat.
- Check for closed valves or obstructions in the boiler piping.
- Verify system is full of water and all air has been purged from the system.
- Check for loose or misplaced jumpers if flow switch or LWCO is not installed.
2. Replace fuse F3 on the control board,
