Furnace locks out on a safety

A limit, rollout, pressure or flame-proving safety opens and the control locks out.

Heating

high

Possible cause

Pressure Switch
Component
Safety switches that prove draft or protect a refrigerant circuit, and how to read what an open switch is telling you.
Limit and Rollout Switches
Component
Temperature safeties that shut down heating equipment, and what each one is actually reporting.

Background

Venting and Draft
Concept
Vent categories, why draft matters, and the failures that put combustion products into the building.

Local Code Notice

HVAC installation, venting, combustion air, ventilation air, gas piping, clearances, termination locations, electrical requirements, permits, and equipment requirements vary by jurisdiction and equipment. Always verify the applicable local codes, adopted code edition, regulations, permits, and manufacturer installation instructions before installation or service.