High limit operation:
Temperature rise across boiler too high.
Flow rate too low.
Check system for:
- Verify boiler and system are full of water.
- Inspect and verify system piping and components.
- Verify piping agrees with boiler manual recommendations.
- Make sure system pressure drop is not too high.
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.
