Slant/Fin Boiler Enable / Interlock Fault

Thermostat calls for heat but boiler does not start, zone circulator runs

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Open safety limit (spill switch, rollout switch), Faulty boiler enable relay on Slant/Fin control, Broken wiring between zone panel and boiler TT

Safety: Do not bypass safety switches. Turn off power before testing.

Steps:

1. Check safety string: Many boilers wire rollout, spill, and limit switches in series. A technician should test continuity through each.
2. Verify TT signal: Confirm 24V is present at the boiler TT terminals when there is a call for heat from the zone panel.

Professional help: Safety devices and interlocks should be diagnosed and replaced by a qualified technician.

Hard 4/5

Rollout Switch

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