Furnace & Heating Questions, Answered

Most furnace repairs in Toronto cost $150–$800 once the $80–$150 diagnostic fee is folded in.

A like-for-like furnace replacement takes 4 to 8 hours — one working day for a two-person crew.

A furnace leaking water is almost always a high-efficiency (condensing) furnace with a blocked, cracked or frozen condensate drain — the unit makes several litres of water a day and it has nowhere to go.

A boom at startup is delayed ignition from dirty burners; banging from the ducts is sheet metal expanding.

A real furnace tune-up in Ontario covers a heat exchanger inspection, burner and flame sensor cleaning, igniter resistance and flame-signal readings, manifold gas pressure set to the rating plate, temperature rise, blower and capacitor checks, a condensate trap flush, venting inspection, safety-control tests and a carbon monoxide reading.

A gas furnace in Ontario lasts 15 to 20 years.

The most common reasons a furnace will not turn on are a thermostat set wrong or dead, a tripped breaker, the furnace power switch flipped off, a blower door not fully closed, a clogged filter that tripped the high-limit, or a full condensate trap opening the float switch.

A brief whiff of gas as the burners light is usually delayed ignition and needs a repair visit soon.

To reset most furnaces, set the thermostat to Off, flip the power switch beside the furnace (or its breaker) off, wait 30 seconds, then turn the power and thermostat back on and give it up to five minutes to run through its start-up sequence.

The most common reason a furnace fan runs constantly is the thermostat fan switch set to On instead of Auto, which tells the blower to run around the clock.

A furnace that clicks but never lights is completing the electrical half of ignition and failing the gas half.

A flashing light on your furnace is a diagnostic code, not a warning lamp.

A furnace pressure switch that keeps tripping is usually doing its job.

A furnace flame sensor costs $150–$300 in the GTA, cleaned or replaced, and that figure normally includes the service call.

A furnace blower motor costs $500–$1,500 installed in the GTA.

Replacing a hot surface igniter costs $200–$450 in the GTA, part and labour, and that usually includes the service call.

A furnace control board costs $500–$1,200 installed in the GTA.

Yes.

Turn the furnace off at its service switch, then clear snow and ice away from both plastic vent pipes by hand or with a soft broom until roughly a metre of open space surrounds each opening.

For most GTA homes a two-stage furnace is worth the extra money, though not for fuel savings — for comfort.

Yes, and oversizing is the most common sizing error we find in GTA homes.

Check it in three steps.

You cannot confirm a crack from outside the furnace, but several signs are worth acting on: a flame that flutters or changes colour the instant the blower starts, soot around the burners, a sharp smell during heating cycles, rust flakes in the cabinet, a rollout switch that keeps tripping, or a carbon monoxide alarm.

No.

Most residential boiler repairs land between $150 and $800, on top of a $90–$150 diagnostic visit that gets credited toward the work.

A cast-iron sectional boiler commonly runs 25 to 35 years, and a well-kept one can pass 40.

A sealed hydronic system only loses pressure when water leaves it, or when the expansion tank stops doing its job.

A typical Ontario home spends around $1,800 a year on gas heat, but almost all of it lands between December and March, so no single monthly figure is useful.

No.

Set it to 15–17°C for a trip of a few days, and no lower than about 12°C for a longer absence — never off.

A furnace that keeps tripping the breaker is either drawing too much current or has a short to ground.

A furnace blower that will not turn on usually has a failed run capacitor, a seized motor, a dead ECM control module or a faulty blower relay on the control board.

A furnace that ignites and then shuts off after 3 to 7 seconds is almost always failing to prove flame.

A furnace that won't shut off when the house is already warm has a stuck call for heat.

A furnace that won't turn on after a power outage usually has a tripped breaker, a thermostat that lost its batteries or settings, a control board locked out by low voltage, or surge damage: a blown 3 A or 5 A board fuse, a failed transformer or a dead board.

A furnace that stopped working after you changed the filter usually has a blower door that is not fully seated, which leaves the door safety switch open and cuts power to the control board.

A furnace lockout lasts until the board resets itself or you cycle the power.

If your furnace condensate line is frozen, switch the furnace off, find the frozen section where the drain passes through a cold space, and thaw it with warm towels or a hair dryer, never an open flame.

A blank thermostat screen means the thermostat has no power.

When a thermostat says heat on but the furnace isn't running, the thermostat is asking for heat and the furnace is not answering.

A furnace that stops working right after a new thermostat goes on almost always has a wiring or setup fault, not a failed furnace.

To tell whether the thermostat or the furnace is the problem, work from wall to basement: is the display on, is it set to HEAT and calling, does the fan run on ON, does the furnace show a fault code.

A boiler that is not turning on has one of three problems: no call for heat is reaching it, a safety is holding it off, or it tried to light and locked out.

Radiators that are cold with the heating on come down to one test: touch the boiler.

One radiator cold while the others are hot is a local fault, not a boiler fault.

To bleed a radiator, turn the heating off and let the system cool, then open the bleed valve at the top corner a quarter turn with a radiator key.

Heating pipes that bang when the heat comes on are doing one of two things.

A boiler making a kettling noise, a rumble, pop or whistle like a kettle coming to the boil, has water flashing to steam on the surface of its heat exchanger.

Boiler pressure is too high when the gauge sits well above its normal 12 to 15 psi cold or nears 30 psi hot, the point where the relief valve opens and starts dripping.

A boiler pilot light that keeps going out usually has a worn or dirty thermocouple, or a dirty pilot orifice giving a weak yellow flame.

A boiler leaking water is usually leaking from one of five places: the relief-valve discharge pipe, a circulator flange or seal, the automatic air vent, a pipe joint, or the condensate drain on a condensing boiler.

A combi boiler that gives hot water but no heating is most often stuck on its hot-water side: the diverter valve has seized in the domestic position, so the burner's heat never leaves the boiler for the radiators or floor loops.

Yes, you can run a gas furnace on a generator.

A gas fireplace that won't light usually comes down to one of four things: a pilot that is out or a thermopile too weak to open the gas valve (millivolt units), a dirty igniter electrode or flame sensor (electronic IPI units), dead batteries in the remote, receiver or wall control, or an appliance gas valve left off since summer.

A gas fireplace pilot light that keeps going out usually has a worn thermocouple or thermopile that no longer holds the gas valve open, or a dirty pilot hood and orifice giving a weak, yellow, lifting flame.

A gas garage heater that won't ignite is stalling at one step of its start sequence: inducer fan, pressure switch, igniter, gas valve, then flame proving.

A furnace making a humming noise is normal when the hum is low and steady: the 24-volt transformer hums whenever the furnace has power.

A rattling furnace is usually something loose: an access panel, cabinet screws, a flue pipe strap or a duct connection, which a homeowner can check with the power off.

A high-efficiency furnace gurgles when condensate water sits where it should drain: in a sagging stretch of vent pipe, a blocked condensate trap, or the pressure-switch hose.

If your furnace igniter glows but the burners won't light, the igniter is working and the gas is not arriving or not catching.

A hot surface igniter should last 3 to 7 years.

A furnace that keeps blowing the 3-amp or 5-amp blade fuse on its control board has a short in the 24-volt wiring, and the fuse is protecting the transformer.

A furnace condensate pump usually stops for one of four reasons: the float is stuck in slime, the motor has failed, the check valve or discharge tube is blocked or kinked, or the pump has lost power at an unplugged cord or a tripped GFCI.

A black furnace filter is usually household soot and fine dust: candles, a wood fireplace, cooking, or a filter left in too long.

A wet furnace filter means water is getting into the return-air side of the furnace, and there are three usual sources: a bypass humidifier leaking down the duct, condensate backing up from a clogged trap or cracked pan, or the air conditioner's coil pan overflowing above the furnace.

Running a furnace without a filter for a few hours, or overnight until the store opens, will not hurt it.

A furnace that stops working after a renovation has usually been choked by dust or cut off by the trades.

A furnace that will not start on the first cold day has usually been caught out by five months sitting idle.

A few small icicles at the end of a high-efficiency furnace's exhaust pipe are normal: the exhaust is cool, water-saturated vapour that freezes as it leaves.

Yes.

A furnace shuts off when it is windy because gusts at the vent termination upset the pressure the furnace uses to prove a safe draft.

A furnace that can't keep up at -25 °C is usually working as designed.

A thermostat reading the wrong temperature is usually in the wrong spot, not broken.

A smart thermostat that keeps losing power or restarting almost always has no C (common) wire.

A Nest thermostat that is not turning on the heat is usually short of power or set up for the wrong equipment.

No heat upstairs with a boiler usually means air or low pressure.

A boiler that keeps shutting off is either short-cycling on its high-limit aquastat or going into lockout.

A boiler circulator pump is bad when the boiler is hot but the pipe a metre past the pump stays cool while the thermostat calls for heat.

A radiator leaking water is usually leaking at a joint, not through the metal: the valve packing nut, the union nut between valve and radiator, or the bleed valve.

Radiant floor heating that is not working has usually lost flow or water temperature in one of five places: a manifold actuator or zone valve stuck closed, air in a loop, a failed circulator, a mixing valve failed or set too low, or a floor-sensor thermostat fault.

One heating zone not working while the others heat normally almost always means a fault that belongs to that zone alone: a failed zone-valve motor, an end switch that never tells the boiler to fire, a dead thermostat or relay, or air trapped in that loop.

Yes.

Yes, in most cases your gas fireplace will work during a power outage.

A carbon monoxide detector chirping once every 30 to 60 seconds is reporting a low battery or the end of its 7-to-10-year life, not carbon monoxide.

On a working appliance it is not dangerous if a pilot light goes out: a thermocouple or thermopile senses the lost flame and closes the gas safety valve, so gas stops flowing.

No.

A gas fireplace that keeps shutting off usually has one of three causes.

A gas fireplace that smells when it is on is usually burning off dust at the first fire of the season, or curing paint if the unit is new; both fade within a few hours of burning.

A garage heater that keeps shutting off is tripping one of its safeties.

Black soot around heating vents is most often ghosting: candle soot and dust filtered out of the air where it leaks past registers and carpet edges.

No.

A radiant tube heater that won't ignite is usually failing its airflow check or its spark.

Fixing a furnace leaking water costs $150–$350 when the cause is a clogged condensate trap or drain line, and $250–$450 for a new condensate pump.

Buy if you can pay cash or qualify for financing; rent only if neither is possible.

A furnace tune-up in Ontario costs $120–$250 for a single visit of 45 to 90 minutes by a licensed gas technician.

You get out of a furnace rental contract in Ontario by paying the buyout in the contract, negotiating it down, or having the contract set aside.

Yes, get a second opinion on a cracked heat exchanger whenever the diagnosis comes without evidence.

Repair a boiler when the fault is a serviceable part, such as a circulator pump, zone valve, expansion tank, relief valve, igniter or aquastat, and the boiler itself is dry and sound.

Yes, a new furnace can be installed the same day or the next day when three things line up: the size you need is in local distributor stock, the new furnace vents the same way as the old one, and an install crew has an open day.

Replacing a furnace heat exchanger costs $1,500–$3,000 in parts and labour on most furnaces.

A furnace inducer motor costs $400–$900 to replace in Ontario, installed.

When you sell a house with a rented furnace, one of two things happens: the buyer agrees in the agreement of purchase and sale to assume the rental contract, or you pay the buyout and the rental company is paid from your closing proceeds.

Most furnace repairs take one to two hours in a single visit: 30 to 60 minutes to diagnose, then 15 to 60 minutes to fit a part carried on the truck, such as an igniter, flame sensor, pressure switch or capacitor.

Yes, in most houses a heat pump can use the existing ductwork, provided the ducts can carry the airflow.

Yes.

A furnace was installed correctly if three things line up: the visible work matches the manual (vent pipes sloped back to the furnace, sealed plenum joints, a trapped condensate drain, a shut-off and drip leg on the gas line), the installer left a commissioning sheet with gas pressure, temperature rise and combustion readings, and the furnace runs long, quiet cycles through its first winter.

Take over a furnace rental only after you have read the contract and done the math.

Yes, you can buy a house with a 20-year-old furnace, but price it as a furnace you will replace.

The size of boiler you need equals your home's heat loss on the coldest design day, calculated room by room to CSA F280 and checked against the radiators or tubing it feeds.

Repair a heat pump that is under 10 years old with a small fault such as a capacitor, contactor, sensor, fan motor or defrost board.

The best time of year to replace a furnace in Ontario is a shoulder season: late April to June, or September to mid-October.

An Ontario landlord who supplies the heat must keep a rental at 20 °C or warmer from September 1 to June 15 under O.

Ontario law gives a landlord no fixed number of hours to fix the heat.

No Ontario law names a yearly furnace tune-up for rentals, but the duties around it come close.

Not in every case.

A like-for-like furnace replacement in an existing Ontario house does not get a routine government inspection.

In practice, yes.

Sometimes.

A boiler replacement takes one to three working days.

Yes.

Most attached two-car garages in southern Ontario need a 30,000 to 45,000 BTU/h gas heater: the smaller size if the walls, ceiling and door are insulated, the larger if they are not.

Buy from whoever will install and service it.

You do not have to register a new furnace for it to have a warranty, but on most brands you have to register it to get the full one.

Yes, within limits.

A furnace warranty is voided or cut short by how the unit was installed and how it has been looked after: installation by someone without a gas licence, an internet purchase with no installing dealer, wrong venting or gas pressure, non-original parts, or moving the furnace to another address.

Partly.

Code 13 on a Carrier furnace is a limit circuit lockout: a limit, draft safeguard, flame rollout or blocked-vent switch stayed open longer than 3 minutes, or the limit tripped 10 times in a row in high heat.

Code 14 on a Carrier furnace is an ignition lockout: the furnace failed to light the gas or prove flame in four attempts, so the control stopped trying.

Code 31 on a Carrier furnace means the pressure switch did not close, or closed and reopened, so the control cannot confirm the vent is drawing.

Code 33 on a Carrier furnace is a limit circuit fault: the limit, draft safeguard, flame rollout or blocked-vent switch is open.

Code 34 on a Carrier furnace is an ignition proving failure: flame was not sensed during the trial for ignition.

Code 41 on a Carrier furnace is a blower motor fault on variable-speed (ECM) models: the blower failed to reach 250 RPM or failed to communicate with the control in time.

1 flash on a Goodman furnace means system lockout: the furnace tried to light three times, failed to establish or hold a flame, and stopped.

On a Goodman furnace, 3 flashes means the pressure switch is stuck open: the inducer fan is running, but the switch that proves draft has not closed, so the burners will not light.

4 flashes on a Goodman furnace means an open main or auxiliary temperature limit switch: the furnace overheated, the burners are locked off, and the circulator blower runs continuously to cool it down.

6 flashes on a Goodman furnace means an open rollout temperature limit switch; Goodman's chart also lists a blown control-board fuse under this code.

7 flashes on a Goodman furnace means low flame sense signal: the flame sensor's micro-amp reading is weak, but the furnace keeps operating normally for now.

Code 3 on a KeepRite furnace means the pressure switch did not close or reopened; on modulating models it refers to the low pressure switch.

Code 4 on a KeepRite furnace means a limit circuit fault: the limit switch or a flame rollout switch is open.

Code 6 on a KeepRite furnace is an ignition proving failure: the flame sensor did not confirm a flame during the trial for ignition.

Lennox furnace error code E223 means the low pressure switch failed open: the switch that proves draft through the vent did not close.

Lennox furnace error code E227 means the low pressure switch opened during the trial for ignition or in run mode: the switch closed, then dropped out.

Lennox furnace error code E228 means combustion air inducer calibration failure: the control was unable to perform its pressure-switch calibration.

Lennox furnace error code E250 means the limit switch circuit is open: the furnace overheated.

Lennox furnace error code E270 is a soft lockout: the furnace exceeded its maximum number of retries with no flame current sensed.

Error E195 on a Nest thermostat means no power to the R wire was detected.

On a Nest thermostat, error E74 means no power is detected on the Rh wire, the 24-volt feed from the furnace or boiler.

N260 on a Nest thermostat is an advisory, not a fault: it means a C wire or Nest Power Connector is recommended.

Code 22 on a Rheem furnace means the main limit or the heat-assisted limit control (HALC) has opened because the furnace overheated.

Code 57 on a Rheem furnace means the pressure switch is stuck open when it should be closed: the control started the inducer but never got proof of draft.

2 flashes on a Trane furnace means the control has locked out because retries or recycles were exceeded: the burners failed to light, or lit and would not stay lit, too many times in a row.

3 flashes on a Trane furnace means an inducer or pressure switch error: the control could not prove that the venting is moving air, so it will not open the gas valve.

4 flashes on a Trane furnace means an open limit or rollout switch: the furnace overheated, or flame left the burner area.

4 red flashes on a York furnace means the main limit switch has opened because the furnace overheated.

7 red flashes on a York furnace means flame could not be established during three trials for ignition.