Lennox sits at the premium end of the Ontario market, and the engineering is real: the modulating SLP98V and the SLP99V that replaced it hold a set temperature tighter and run quieter than almost anything else we put in a basement. The same design philosophy is why a repair bill can surprise you. Lennox specifies its own control boards rather than a generic industry part, so when one fails it is a Lennox-numbered board and Lennox's own channel is where it comes from.
Around Burlington we see a lot of Lennox in Tyandaga and Aldershot, where the 1970s and early-1980s houses are typically on their second or third furnace. Most of those units are mechanically sound and want nothing more than a flame sensor, a proper burner cleaning and a fresh filter. A few basements still hold a Lennox Pulse — the pulse-combustion furnace Lennox sold from the early 1980s into the 1990s. It was remarkable for its day. Today every fault on one turns into a parts hunt, and we will tell you that on the phone rather than after the invoice.
For GTA housing stock, the argument for Lennox is the long low-fire cycle. A two-stage or modulating furnace in the Elite or Signature range runs quietly at partial output for most of the winter instead of blasting and shutting off, which is exactly what a drafty two-storey with long duct runs to the back bedrooms needs. If your complaint is that one room never keeps up, staging and blower speed usually matter more than the brand on the door — see why one room is always cold before you shop for equipment.
One thing to be clear about: ZK Mechanical is an independent, owner-operated contractor. We are not part of Lennox's dealer network and we do not sell brand loyalty. That has a practical upside for you — nobody here has a quota that says the answer has to be another Lennox.
Lennox lines we install and service
The top tier: the modulating SLP99V gas furnace (and the SLP98V it succeeded), the XC25 air conditioner and the SL25XPV variable-capacity heat pump. These are fully communicating systems — furnace, outdoor unit and iComfort thermostat share a four-wire RSBus, which means a wiring fault presents as an equipment fault until somebody actually meters the bus.
The two-stage middle of the range: EL296V and EL296E furnaces, EL16XC1 and XC16 condensers, and the Elite-badged heat pumps that pair with them. This is where most Burlington and Oakville replacements land, because two-stage heat with a variable-speed blower solves the cold-bedroom complaint without paying for full modulation.
Single-stage and builder-grade: the ML196 condensing furnace and the ML14XC1 condenser. Nothing is wrong with them, and they are the cheapest Lennox to keep alive because the parts are simple — but they run flat out or not at all, and you will hear every start. Lennox's 80% AFUE Merit furnaces are not an option on a new install here: Canada's federal minimum for a residential gas furnace is 95% AFUE.
S30, M30 and E30 thermostats, plus PureAir air purifiers and Healthy Climate media filters mounted at the furnace. When an iComfort screen reports a communication loss, the cause is far more often a pinched or corroded splice in a joist bay than the thermostat itself.
The G-series furnaces — G26, G40, G51 and G61 — and the Pulse. We still service them, but be realistic about the odds: inducer assemblies and integrated boards for discontinued Lennox platforms are order-in items when they can be had at all, and at some point the sensible money moves to a replacement.
What goes wrong on Lennox equipment
Three ignition tries, then lockout — flame sensor or SureLight igniter
The burner lights, runs five or six seconds, drops out, tries twice more and quits. In most cases the flame sensor rod is coated and needs cleaning or replacing: $150–$300. If the igniter never glows at all, a Lennox SureLight silicon nitride igniter is $200–$450 installed. Silicon nitride is tougher than the older silicon carbide igniters, but a nitride igniter that has stopped glowing is done; we fit a new one rather than reseating the old.
Pressure switch will not close — the condensate trap is silted up
Condensing Lennox furnaces drain through a trap and an inducer drain port that fill with the fine pale scale that washes out of a secondary heat exchanger. The board reads the blockage as no draft and refuses to light. Clearing the trap and drain runs $150–$350. If it plugs again inside a year, the drain slope or the trap fitting is wrong — that is an installation defect, not a maintenance failure.
iComfort communication loss — the system falls back to a default
On a Signature or Elite communicating setup, a broken RSBus leg leaves you with heat but no staging, no proper blower ramp and a thermostat that keeps throwing an alert. We meter the bus end to end before touching the equipment, because replacing a perfectly good thermostat is an expensive way to not fix a splice. The usual failure point is a splice in a joist bay or a terminal at the outdoor unit, not the board.
XC condenser hums but the fan will not spin
Almost always the run capacitor or a pitted contactor: $150–$350 either way, one visit, and the system cools before we leave. Worth checking while we are there — many Lennox condensers around here sit on elevated stands, and a stand that has settled toward the house puts the unit out of level and hard on the compressor. If the outdoor board is reporting instead, our Lennox AC error codes reference decodes what it is showing.
Lennox warranty: what to know
- Register within 60 days of installation. Lennox's enhanced residential parts term runs from the install date and depends on the serial number being registered inside that window at Lennox's warranty registration page. Miss it and the unit keeps only the base term.
- Parts are covered; labour never is. A warranty claim gets you the component. The diagnostic and the hours to fit it are yours from day one unless a contractor sold you a separate labour policy in writing.
- Heat exchanger terms differ by line. Lennox publishes its longest heat exchanger coverage on the premium gas furnaces and a shorter term further down the range. Which one applies is printed on the certificate for your exact model — do not assume yours matches the neighbour's.
- Coverage follows the original owner at the original address. Selling the house generally shortens or ends the enhanced term, and any transfer has its own window and conditions. Check before you list, not after closing.
- What puts a claim at risk: an install by someone without a gas licence, equipment sized outside the published range, and years with no maintenance record. Keep every invoice in the same envelope as the manual — see what your HVAC warranty actually covers.
Parts availability in the GTA
Lennox is the one major brand whose parts do not sit on a general wholesaler's shelf. Components move through Lennox's own parts stores, which is excellent when the item is a stocked consumable — igniters, flame sensors, pressure switches, capacitors, filters and humidifier pads are same-day pickups for a GTA contractor, so a routine Lennox breakdown is a one-visit fix. It gets slower at the specialized end: integrated control boards, variable-speed blower assemblies and inducer housings for older or discontinued platforms are frequently order-in, and on a Pulse or an early G-series they may simply be gone. We check availability before we quote a part rather than after, so you are not sitting in a cold house waiting on a box that was never coming.
Lennox Furnace Error Codes Explained — what each one means and whether it is safe to keep running.
Common questions
Do I have to use a Lennox dealer to get my Lennox furnace repaired?
No. Any TSSA-licensed gas technician can legally service and repair Lennox equipment in Ontario, and the manufacturer's parts warranty stays attached to the equipment, not to whoever installed it. What changes is where the component comes from and how a warranty claim gets filed. We will tell you plainly when a claim is worth pursuing and when buying the part outright is faster.
My Lennox furnace is flashing a light instead of showing a code. What does it mean?
Older Lennox boards blink a pattern rather than printing a number, and the legend for that pattern is on a label inside the blower compartment door — that label wins over anything you read online, because it is written for your exact board. Count the flashes, note the colour, then check the pattern against our Lennox furnace error codes reference.
Is a Lennox worth the premium over a value brand?
Sometimes. The Signature and Elite equipment genuinely runs quieter and holds temperature better, and if you are sensitive to noise or humidity swings you will notice it. But the installation quality decides more of the outcome than the badge does — a well-commissioned mid-tier furnace beats a premium one that was never set up properly. Our answer on whether furnace brand really matters works through the trade-off.
Can you put a new Lennox condenser on my existing Lennox furnace?
Often, but not automatically. The indoor coil has to match the outdoor unit's capacity and metering device, the line set has to be the right diameter and clean, and new equipment now ships on an A2L refrigerant — R-454B on current Lennox — rather than the R-410A in your old system. We measure the existing coil and line set before quoting, because a mismatched pair costs you efficiency every summer for the next fifteen years.
What does a new Lennox furnace cost installed in the GTA?
High-efficiency furnace installs run $4,500–$7,500 depending on tier, sizing, venting and what the sheet metal needs. A single-stage Merit sits at the bottom of that band and a modulating Signature at the top. If your air conditioner is also near the end of its life, doing both together typically runs $7,500–$11,500 and saves a full crew mobilization — we handle the rebate paperwork either way.