A gas smell or a sounding carbon monoxide alarm comes before everything else
If you smell gas, leave the house first and call Enbridge Gas, which supplies natural gas to the Town of Grimsby, from outside. Do not switch lights or the furnace on or off on the way out. If a carbon monoxide alarm sounds, get everyone outside and call emergency services before you call us about the furnace.
The furnace fault most often behind a carbon monoxide concern is a cracked heat exchanger. The heat exchanger is the metal chamber that keeps burner exhaust separate from the house air the blower moves; a crack lets combustion gases mix into that air. It is the one fault we will not leave running. The Ontario Fire Code requires a working carbon monoxide alarm next to each sleeping area of any home with a fuel-burning appliance, a fireplace or an attached garage, so if yours are missing or past their date, replace them now.
No heat usually means the ignition sequence stopped at one step
A gas furnace lights in a fixed order: the thermostat calls for heat, the inducer motor starts and pulls air through the heat exchanger, a pressure switch confirms that draft, the hot-surface igniter glows, the gas valve opens, and the flame sensor proves there is a flame. If any step fails, the control board stops and usually flashes a code. A thermostat with dead batteries, a cracked igniter and a flame sensor coated in residue are the common simple causes; an inducer motor with worn bearings and a failed control board are the larger ones.
In the newer homes of the west end, around the Winston Road Neighbourhood and the GO Station Secondary Plan Area, high-efficiency condensing furnaces vent through plastic pipes in the side wall. When those terminations ice over or a drift covers them, or when the condensate trap freezes or clogs and water backs up, the pressure switch never closes and the furnace will not light. Check that the outside pipes are clear before you call. Our guide to a furnace running but not heating the house walks through the safe checks and how to reset the furnace.
Cold air from the vents means the burners are not staying lit
If the blower runs but the air is cool, the furnace is either failing to hold a flame or running the fan without a call for heat. A weak flame sensor signal makes the board shut the gas off a few seconds after lighting, then the blower runs on to cool the heat exchanger, which feels like cold air. A thermostat fan setting left on, a gas valve that opens only partly, or low gas pressure at the manifold produce the same complaint for different reasons.
The technician separates these by measurement rather than by swapping parts: flame sensor current in microamps, inlet and manifold gas pressure, and the temperature rise between the return air and the supply air while the burners run.
Short cycling points to airflow, flame proving or venting
A furnace that runs for two or three minutes, shuts off and restarts is usually protecting itself. The most common cause is the high-limit switch, a temperature sensor on the heat exchanger that cuts the burners when it gets too hot. It trips because too little air is moving: a clogged filter, closed supply registers, a weak blower motor, or ductwork too small for the furnace.
That last cause is common in the post-war houses of the Lakemount Terrace Subdivision in Grimsby's north end, where furnaces were converted from oil or coal to gas and later replaced, often on the original undersized ducts and weak returns. The technician measures external static pressure, which is the resistance the blower is pushing against, to show whether the duct system is the problem. Sometimes the right fix is a return-air change rather than a part. A furnace that is too large for the house will also short cycle, which is worth knowing before any replacement.
Noises tell you which part is wearing
A loud bang at start-up is usually delayed ignition: gas builds up before it lights, often because of dirty burners or a weak igniter. A rising whine or grinding from the furnace at start-up usually comes from the inducer motor bearings. A squeal while the fan runs points to the blower motor or, on older units, a belt. Rattling can be a loose panel or a failing blower wheel; a gurgle in a condensing furnace means water is not draining from the condensate trap or lines as it should.
In the older houses of Grimsby Beach and along Main Street East and West, furnaces were often fitted later into spaces built for wood or coal, and some still vent into old chimneys. A furnace that sounds normal but leaves soot or spills exhaust at the draft hood may be venting into a chimney that needs relining, and the technician will check this before calling the repair done.
A repair visit starts with measurement and ends with your approval
The technician confirms the symptom with you, reads any fault code, and tests the system before naming a cause. On most visits that includes gas pressures, flame sensor signal, inducer draft against the pressure switch setting, temperature rise, blower amperage, and a combustion and carbon monoxide reading in the flue. You are shown what was found and given the price in writing, and nothing is fitted until you approve it.
Work is performed by TSSA-certified gas technicians, as Ontario Regulation 212/01 requires for anyone who services or repairs a gas appliance, and repairs follow the CSA B149.1 installation code. If the furnace is old and the fault is a major one, we will say whether the repair is worth making; our guide on whether a 25-year-old furnace should be repaired or replaced explains how to weigh it. To arrange a visit, use the contact page or request a quote.