High limit operation: Outlet water temp. increased too quickly. Non-adjustable default setting 9.8°F/sec
1. Indicates flow rate too low. Check system for:
- Verify boiler and system are full of water.
- Make sure system does not have trapped air.
- Inspect and verify system piping and components.
- Verify piping agrees with boiler manual recommendations.
2. Verify operation of boiler circulator:
- Check voltage at circulator junction box to ensure 120 vac when boiler operates. If no voltage, check wiring and wiring connections.
- High voltage terminal strip terminals 5 and 6 should show 120 vac for space heating; terminals 3 and 4 should show 120 vac for DHW. Replace circulator if powered but not operating.
- Replace line voltage wire harness if necessary. Replace control module if wire replacement doesn’t resolve.
