Gas Fireplace Not Turning On? 12 Causes and Fixes (GTA Guide)

Why gas fireplaces stop turning on

A gas fireplace is a simple system with a handful of points of failure: a pilot or igniter that starts the flame, a sensor that proves the flame is lit, a valve that controls gas flow, and a switch or remote that tells it to start. When any one of those links breaks, the whole system refuses to light rather than lighting unsafely - which is exactly how it is designed to work. This guide walks through the 12 most common reasons GTA homeowners call us for a fireplace that will not turn on, roughly in the order we actually find them.

Millivolt vs IPI: know which system you have

Most GTA gas fireplaces built before roughly 2010 use a millivolt system: a standing pilot light burns continuously (or is lit manually each season) and generates a tiny electrical current through a thermopile, which powers the gas valve's magnet and the wall switch circuit. No household electricity is involved.

Newer units use IPI, intermittent pilot ignition: a control module sends a spark to light the pilot only when you press the remote or switch, confirms the flame with a sensor, then opens the main valve. IPI systems need a functioning circuit board and batteries (or a plug-in transformer) to work at all - a dead battery pack is the single most common IPI no-start we see in the GTA.

The safe homeowner checklist

Run through these steps in order before assuming the worst. Each one takes a couple of minutes and none of them require opening the gas valve assembly or touching wiring.

1. Check the wall switch and remote batteries first - replace with fresh batteries even if the old ones test as 'okay', since low voltage under load is a common false-positive.
2. Confirm the main gas shutoff valve behind or beside the fireplace is turned fully parallel to the gas line (open), not perpendicular (closed).
3. Look through the glass or access panel for the pilot flame - if it is out, follow the lighting instructions on the plate inside the unit (usually pilot knob to 'pilot', press and hold, ignite, hold 30-60 seconds).
4. If the pilot lights but will not stay lit after you release the knob, this points to a weak thermocouple or thermopile - stop here and book a technician rather than repeatedly re-lighting it.
5. Reset the wall switch and remote by turning the system off, waiting 60 seconds, and trying again - this clears a false ODS or high-limit trip in some models.
6. Check that nothing is blocking the exterior vent termination (snow, leaves, a bird nest) if the unit is direct-vent - blocked venting is a common winter cause across the GTA.
7. Confirm no other gas appliance issue exists in the home (furnace, water heater, stove) - if none of them work, the problem is upstream at the meter or supply line, not the fireplace.
8. If none of the above resolves it, stop resetting the system repeatedly and book a licensed gas technician - repeated resets on a real fault can mask a developing safety issue.

The 12 causes, explained

1. Dead pilot light

Drafts, a dirty pilot orifice, or simply age can cause a standing pilot to go out. Relighting it per the manufacturer's plate usually resolves a one-off outage. If it goes out repeatedly within days, move to cause 2.

2. Weak or failed thermocouple

The thermocouple is a small sensor that sits in the pilot flame and generates a tiny voltage that holds the gas valve's safety magnet open. When it weakens with age, the valve senses 'no flame' even when the pilot is lit, and shuts the gas off within seconds of you releasing the knob. This is the single most common millivolt-system fault we replace, and parts cost $15-$40 with an installed price typically $120-$220 including the service call.

3. Failed thermopile

Similar to a thermocouple but generates enough voltage to also power the wall switch and remote circuit, not just hold the valve open. A failed thermopile often shows as: pilot lights and stays lit, but the main burner never ignites when you turn the wall switch on. Replacement runs $150-$300 installed.

4. Dead remote or wall switch batteries

IPI systems rely on a battery pack (often 2 AA cells) to power the control module and receiver. Weak batteries commonly cause intermittent operation - the unit lights some days and not others - before failing completely. Always replace with fresh batteries as a first step, not last.

5. Corroded battery contacts

Even fresh batteries fail to power the system if the contact springs inside the battery holder have corroded, common in units near a humid basement or a bathroom-adjacent chimney chase. A quick clean with a pencil eraser or fine sandpaper on the contacts often restores function.

6. Gas supply valve not fully open

The shutoff valve on the gas line feeding the fireplace, often behind an access panel, must be turned fully in line with the pipe to be open. A valve left even slightly off-axis after a chimney sweep, carpet installation, or renovation can starve the pilot of gas.

7. Tripped ODS (oxygen depletion sensor)

Vent-free gas fireplaces include an ODS that shuts the gas off if oxygen levels in the room drop too low, a real safety feature rather than a nuisance fault. Repeated ODS trips mean the room is under-ventilated or the burner is not combusting cleanly, and it should be diagnosed by a technician rather than reset repeatedly.

8. Tripped high-limit switch

This switch shuts the unit down if internal temperatures climb too high, often because a blower has failed, a vent is restricted, or the unit was run for an unusually long continuous period. It typically resets automatically once the unit cools, but repeated trips point to an airflow or venting problem underneath.

9. Blocked or damaged venting

Direct-vent units terminate through an exterior wall or roof cap, and in the GTA that termination is a magnet for snow drifts, ice buildup, and bird or squirrel nests in the fall. Some units have a pressure switch that will not allow the burner to start at all if venting is restricted, which shows up as a fireplace that clicks or attempts to light but never sustains a flame.

10. Faulty gas valve

Gas valves themselves fail less often than the sensors around them, but a stuck or electrically failed valve will prevent gas flow even when every other component tests fine. This is a technician-level diagnosis and repair, and valve replacement typically runs $250-$450 installed depending on the model.

11. Control board or IPI module failure

On IPI systems, a failed control board means no spark at all, or a spark that never confirms flame sense and shuts down after a few seconds. This is one of the pricier fixes, typically $300-$550 installed, but it is far less common than a simple battery or sensor issue.

12. Wiring or wall switch fault

Low-voltage wiring between the wall switch and the fireplace can be pinched, chewed by rodents in an unfinished basement run, or simply loose at a connector. A technician can test continuity in a few minutes; this is one of the less common causes but is worth ruling out if everything else at the unit tests fine.

Typical GTA repair costs by cause

When to stop troubleshooting and call a licensed gas technician

• Any smell of gas, at any point in the process - stop immediately and follow the gas leak safety steps above.
• The pilot lights but will not stay lit after two attempts following the manufacturer's instructions.
• The ODS or high-limit switch trips more than once in a short period.
• Soot marks appear above the fireplace opening or on the glass, which can indicate incomplete combustion.
• The unit is more than 15 years old and has never had a professional service or safety inspection.
• You are not fully confident reading the lighting instructions plate or locating the gas shutoff valve.

Gas fireplace repair in Ontario involving the gas valve, control module, or venting must be performed by a licensed gas technician (G2 or higher), consistent with CSA B149.1 and TSSA regulation. A technician working on your unit should be able to show you their TSSA registration number without hesitation.

Preventing the next no-start call

An annual gas fireplace service before the heating season, typically $150-$220 in the GTA, includes cleaning the pilot and burner, testing the thermocouple or thermopile output, checking the venting for blockage, and replacing remote batteries as a matter of course. Most of the 12 causes above are caught and corrected during that visit before they turn into a no-start call on the first cold night of the year.