Pilot light will not stay lit: what is wrong and what the fix costs in Fort Collins

A pilot that lights and then drops out the second you release the knob is almost always the thermocouple, and in Fort Collins it is almost always October. The service call is $150 to $300, a thermocouple or thermopile is $200 to $400 installed, and a full pilot assembly is $300 to $600. Most of these are one visit and under an hour of work.

The mechanism explains everything else on this page. On a standing-pilot fireplace the pilot flame wraps a thin metal probe, the thermocouple. Heat makes it produce a tiny voltage, and that voltage holds a magnet inside the gas valve open. Holding the knob down holds that magnet open by hand; letting go hands the job to the thermocouple. Weak voltage, magnet drops, pilot dies. It is a safety device working as designed on a sensor that has quietly failed.

Check this first

Two minutes, no tools, nothing that involves touching gas fittings.

1. Is the gas valve handle in the on position? On most units it is a small lever or knob behind the bottom louver, marked ON, OFF, and PILOT. If someone shut it off in April, that is the whole story.
2. Look at the pilot flame while you hold the knob. A healthy pilot is a firm blue flame that wraps the sensor probe with a soft yellow tip. A pilot that is small, lifting off, orange, or dancing away from the probe is not heating the sensor, and that is a cleaning problem more than a parts problem.
3. Count the hold. Thirty to sixty seconds with the knob fully depressed is normal. Note how long you held it and whether the pilot died instantly or faded over a few seconds. That detail tells us whether it is the sensor or the valve magnet.
4. Stop after two tries. Each failed relight puts a little unburned gas in the box. Two attempts, five minutes apart, then stop.

Do not clean the pilot orifice yourself, bend the probe, or take the burner apart. A bent electrode or a cracked pilot tube turns a $250 repair into a $700 one.

What is usually wrong

Every number here is the same range on the pricing page, and the pilot and ignition repair page explains the millivolt test that separates a bad sensor from a bad valve in about ninety seconds.

Why this happens here

Six months off. Fort Collins fireplaces sit cold from roughly April to October. Dust, pet hair, and drywall grit settle into the pilot hood, and spiders build in the small openings, because the pilot orifice is exactly the kind of warm, sheltered hole they like. The first cold night the pilot lights small and yellow and cannot heat the probe. That single failure mode makes it the busiest week of the year for hearth techs.

Age of the stock. The south Fort Collins and Harmony corridor subdivisions went up with factory direct-vent fireplaces in the 1990s and 2000s. Those units are 20 to 30 years old on their original thermocouple. Old Town and the 1970s ring have masonry fireplaces retrofitted with gas log sets on manual valves, which are even simpler and even older.

Altitude, indirectly. The National Fuel Gas Code calls for derating gas appliances above 2,000 feet by about 4 percent per 1,000 feet, and Fort Collins is at 4,997. A unit that never got its high-altitude orifice runs rich everywhere, including at the pilot, which soots the probe and insulates it from the flame. If your pilot trouble came back within a season of the last fix, ask about the orifice.

When it is a safety issue

Stop and treat it as an emergency if you smell gas: leave the house, leave the door open behind you, do not touch a light switch or a garage door opener, and call your gas utility’s emergency line or 911 from outside. Do not call a fireplace company first, and do not go back in to shut anything off.

Short of that, a pilot that will not hold is a fireplace that is off, which is safe. What is not safe is repeated relighting, flame rollout at the front of the firebox, or soot marks on the wall above the opening. Any of those, leave it off and book the safety inspection and leak check.

What to expect on the call

Send three things: the model number from the rating plate inside the bottom louver, whether the pilot burns all the time or sparks on demand, and what you saw during the hold. That lets us bring the right thermocouple, thermopile, or pilot assembly the first time.

On site our tech leak-checks the valve and fittings, measures sensor output in millivolts against the 300 to 750 millivolt band a healthy thermopile should produce, cleans the pilot assembly and burner ports, replaces what failed, and test-fires from cold. You get the readings in writing. If the pilot only needed cleaning, the visit is the service call and nothing more. Book it in September or October and skip the December queue, which is what the annual service page is really about.