Heating | Canada

Gas Furnace Sequence of Operation and Safeties

A quick ladder for no-heat calls so you can prove exactly where the sequence breaks.

Built for Canada field work where furnaces, air-source heat pumps, hydronic add-ons, and cold-climate comfort expectations all hit the same crew.

Ticket note prompts

Document the last successful step in the heat sequence so a repeat callback starts from the real failure point.
Note draft, ignition, flame-sense, and blower behavior separately instead of writing only 'no heat'.
Capture any venting, filter, or temperature-rise condition that contributed to a limit or rollout issue.

Comeback prevention

Confirm the furnace runs through a complete heat cycle with normal temperature rise before you leave.
Recheck venting and condensate routing on high-efficiency furnaces when pressure-switch faults were involved.
Verify flame signal stability after cleaning or grounding repairs.

Sequence ladder

Start with thermostat call and board status, then prove line voltage and low voltage at the right moments.
Listen for inducer start, then confirm pressure switch closure instead of assuming it happened.
If flame lights but does not hold, clean and prove flame sense before selling a gas valve.

Failure points

Step	If it fails here	Likely direction
Inducer never starts	No sequence initiation	Board, door switch, line voltage, or call issue
Pressure switch never proves	Draft path not proven	Blocked vent, cracked hose, weak inducer, switch issue
Ignition lights then drops	Flame not proven	Flame sensor, grounding, board, or gas delivery issue

Safety mindset

A tripped rollout means stop and inspect for flame carryover, blocked exchanger path, or venting trouble.
Repeated high-limit trips point to airflow, blower, filter, or temperature-rise problems before they point to a bad limit.
Do not leave jumpers in safety circuits after proving the fault path.

Use This Sheet For

Use it to separate ignition faults, airflow safeties, pressure-switch problems, and board logic failures.

Quick Hits

Know the sequence cold: call for heat, inducer, pressure switch, ignition, flame sense, blower on, limit monitoring.
If the sequence repeats and drops out, prove which safety or proof circuit is losing status.
High limits and rollout trips are symptoms first and replacement parts second.

Canada heating lens

Heat strips, dual-fuel staging, and furnace recovery all deserve separate notes because comfort complaints can hide the real operating mode.
Defrost complaints should include how the home felt and whether supplemental heat actually carried the load.
Pressure-switch, condensate, and venting notes are especially valuable when outdoor conditions change between visits.

Country operating lens

Units and measurements

Field work often mixes CFM and in. w.c. with metric references, so consistency in the ticket matters.
Cold-weather operation changes what 'normal' looks like for temperature rise, defrost behavior, and occupancy complaints.
Combustion and gas notes should reflect the provincial and utility expectations that apply to the site.

Code and handoff reminders

Provincial fuel-gas, electrical, and refrigeration requirements should guide the repair language and handoff.
Manufacturer low-ambient data and commissioning steps matter on heat-pump calls that drift into guesswork.
When a system is left operating with known limitations, document that limitation clearly before you leave.

Safety Note

Treat these as field notes, not manufacturer data. If the equipment label, service manual, combustion analysis, or local code disagrees, those sources win.