Furnace Repair in Durham Region: 7 Common Problems and When to Call HVAC Zack
When colder weather hits and furnaces across Durham Region start up for real, small issues can turn into no-heat calls. Some problems are safe to monitor for a day. Others need a technician right away.
This guide walks through common furnace issues, what you can check yourself, and when to call HVAC Zack for professional repair.
1. No heat at all
If the thermostat is set to Heat and the furnace never starts, check the basics first. Confirm the thermostat has power, the system switch is on, and the furnace switch or breaker has not been flipped. If everything appears normal but the unit will not start, it is time to book furnace repair service.
Short clicking or a brief start followed by shutdown can point to ignition or safety lockout issues. Do not keep resetting the system. Safety controls are there to protect your home.
2. Furnace running but blowing cold or cool air
Warm air should arrive within a few minutes of start-up. If the blower runs steadily but the air feels cool, the burners may not be lighting or they may be going out quickly. Shut the system off and call for service. We will check ignition, flame signal, gas supply, and the temperature rise across the heat exchanger.
If the air is warm but not hot and comfort is poor room to room, airflow and duct design may be part of the problem. Our duct design guide explains why returns and static pressure matter.
3. Short cycling or constant running
A furnace that turns on and off every few minutes wastes energy and wears components. Common causes include restricted airflow, a dirty filter, an oversized furnace, or safety limits opening. Replace the filter and make sure supply and return registers are open. If short cycling continues, request a diagnostic.
On the other side, if the furnace runs almost constantly and still struggles to hold temperature, it may be undersized for the load or fighting duct and insulation issues. We can measure temperature rise and static pressure to see what is really going on.
4. New noises or vibrations
Low, steady blower noise is normal. New or worsening sounds are not. Pay attention to:
Metallic scraping or grinding
Loud rattles or buzzing
Booming or rumbling on ignition
Whistling from returns or grilles
Some noises point to loose panels or minor adjustments. Others suggest bearing wear, blower wheel damage, or combustion problems. If you hear anything sharp or alarming, shut the system off and contact us for furnace repair before the issue grows.
5. Odors and safety concerns
A light dusty smell for the first few minutes at the start of the season is normal. Persistent burning odors, sharp electrical smells, or anything like melted plastic are not. If you ever smell raw gas, hear your carbon monoxide alarm, or feel unwell, leave the home and call emergency services before contacting an HVAC technician.
After the immediate concern is handled, we can perform a start-up and safety check to inspect the heat exchanger, venting, gas line, and controls.
6. Thermostat and control issues
Sometimes the furnace is fine but the controls are not. Weak thermostat batteries, miswired stats, or incorrect settings can cause no-heat, short cycling, or systems that only work in fan mode. If you recently replaced the thermostat and the furnace has not behaved properly since, we can verify wiring, setup, and staging.
For hybrid systems that combine a heat pump with a furnace, we also confirm outdoor sensors and lockout temperatures. If you are new to hybrid setups, our heat pump overview explains how they share the workload in winter.
7. Older furnaces and repeated repairs
If your furnace is over 15 years old, uses standing pilot ignition, or has needed multiple repairs in recent seasons, it may be time to compare repair costs with replacement. Major items like a cracked heat exchanger or control board failures can push an older unit past the point where further repairs make sense.
In those cases, we quote both options: a focused repair estimate and a replacement path, sometimes including a cold-climate heat pump with a high-efficiency furnace as backup. Financing can help spread the cost of a new system so you do not put off a necessary upgrade. Details here: HVAC Zack financing options.
Why work with HVAC Zack for furnace repair
On a typical furnace repair visit we:
Listen to the symptoms you have noticed
Inspect filters, airflow, venting, and safety controls
Diagnose ignition, gas, electrical, or control issues
Explain findings in plain language and share photos where helpful
Give you a clear repair or replace path before we proceed
When repairs are completed, we test the furnace through a full heat cycle and confirm that the thermostat, safeties, and blower are working as they should.
We serve homeowners across Pickering, Ajax, Whitby, Oshawa, Courtice, and Bowmanville. If you are specifically in Oshawa or Whitby, you can learn more on our local service pages: HVAC services in Oshawa and HVAC services in Whitby.