What the Tags and Stickers a Tech Leaves Behind Mean

Why this matters

After most service visits, something small stays behind: a sticker on the furnace door, a date written on the filter, a signed card on the electrical panel, and sometimes a bright red tag hanging from a gas valve. Most of these are records, useful the next time anyone works on the equipment and when you sell the house. One of them is a warning that the equipment is not safe to use, and it is the one people most often ignore, peel off, or inherit from a previous owner without understanding.

This card shows the four you are most likely to find, what each one is telling you, and what you do about it.

The four you are most likely to find

[1] SERVICE STICKER  (inside furnace or AC panel door)
+------------------------------------------------+
| SERVICED BY: company name, phone               |
| DATE: 10/14/2023        TECH: J.R.             |
| WORK: heating tune-up, flame sensor cleaned    |
| FILTER: 16x25x1         NEXT DUE: fall 2024    |
+------------------------------------------------+

[2] FILTER DATE  (marker on the filter frame)
      IN 09/02/26        AIR FLOW ---->

[3] INSPECTION STICKER  (inside panel door)
+------------------------------------------------+
| CITY BUILDING DEPT    ELECTRICAL               |
| PERMIT NO. E19-0412   FINAL: APPROVED          |
| INSPECTOR: 27         DATE: 06/11/2019         |
+------------------------------------------------+

[4] RED TAG  (wired to the furnace gas valve)
+------------------------------------------------+
| DANGER  DO NOT OPERATE                         |
| APPLIANCE: furnace    DATE: 03/04/2026         |
| CONDITION: flue gas spilling at draft hood     |
| GAS VALVE: OFF, tagged                         |
| ISSUED BY: technician name, company            |
| DO NOT REMOVE until repaired and rechecked     |
+------------------------------------------------+

Service stickers: the equipment's logbook

A service sticker is the technician's note to whoever opens the equipment next. It usually carries the company, the date, the work done and sometimes the filter size and a next-due date. Some companies stick a fresh one on top of the old one each visit, so the stack itself becomes a history.

What it tells you. When the equipment was last looked at, by whom, and what was found. If the last date is several years old, the equipment has gone without the routine checks its maker expects. If the "work" line names a repair, that part has a history worth mentioning to the next technician.

What it does not tell you. That the equipment is in good shape today. A sticker from three years ago is a record of three years ago.

What to do. Photograph it, inside and out, so you have it even if it fades or the panel gets replaced. Leave the sticker itself where it is.

Filter dates: your reminder, written where you will see it

Many technicians, and many careful owners, write the install date on the edge of a new filter with a marker, next to the arrow showing which way air flows through it.

What it tells you. How long the filter has been in. Many 1-inch filters are rated for one to three months; thicker media filters often last longer. The date plus the filter's own rating tells you when it is due.

The arrow matters too. It should point toward the furnace or air handler, the direction the air travels. A filter put in backward catches less and can collapse.

What to do. When you change it, write the date on the new one. See related: How to Change Your Furnace Filter.

Permit and inspection stickers: proof someone independent checked

When work is done under a building permit, the local building department sends an inspector, and many departments leave a sticker, a signed card or a stamp when the work passes. You may find one inside the electrical panel door, on a water heater, by the furnace, or on a permit card stapled near the work. During a job, a permit card may also be posted in a front window so the inspector can find the job.

What it tells you. The permit number and that a named inspection passed on that date. "Final" or "final approved" means the last required inspection passed and the permit should be closed. A sticker for a rough-in or an intermediate inspection is not the same thing; it means work could continue, not that it was finished and signed off.

What to do. Write down the permit number and photograph the sticker. If you want to know whether a permit was actually closed, many building departments let you look up a permit number online or by calling. See related: What a Permit Means for You as the Homeowner.

The red tag: do not use this appliance

A red tag is different from everything else on this card. It is a written statement that a gas utility worker or a technician found a condition on that appliance, or on the gas service, that they judged unsafe, and that they shut it off.

Common reasons for one: a gas leak, exhaust gases or carbon monoxide coming into the house instead of going up the vent, a cracked or damaged part in the burner or heat exchanger area, a vent that is disconnected, blocked or the wrong type, or an installation that does not meet the safety requirements the inspector applies. The tag usually names the condition.

What it means for you:

• Do not relight, turn on or use the appliance. Do not turn the gas valve back on, and do not reset or restart it.
• Do not remove the tag. It is there to stop the next person, including a family member or a future buyer, from using it.
• It is not a repair. A red tag means the appliance was made safe by shutting it off. The condition that caused it is still there until someone fixes it.

Getting it cleared. A licensed technician in the right trade makes the repair or replacement and confirms the condition is gone. Who then removes the tag and turns the gas back on depends on where you live and who issued it: some gas utilities want to return themselves, especially when they shut off the gas at the meter; others accept the repairing contractor's sign-off. Ask the technician who issued it, or call the gas utility, which process applies to yours.

If there is a red tag on the gas meter itself, gas service to the whole house was shut off. Only the gas utility restores that.

If you have no heat because of a red tag in cold weather, say so when you book the repair. Many companies prioritize no-heat calls. Until it is fixed, use only electric space heaters plugged directly into a wall outlet, kept 3 feet from anything that can burn, and never a grill, camp stove, generator or oven to heat the house. Make sure your carbon monoxide alarms work.

If anyone smells gas or a carbon monoxide alarm sounds, that is not a tag question. Everyone leaves, and you call 911 or the gas utility from outside. See related: How to Respond If You Smell Gas in Your Home.

Others you may come across

Worked example: four tags in a house you just bought

The setup. A family closes on a house in early November 2026. On the first cold night they go to turn the heat on and find four things in the basement.

The furnace panel door has a service sticker from 10/14/2023: heating tune-up, flame sensor cleaned, next due fall 2024. That is about three years since the last recorded service, and the next-due date passed two years ago.

The filter is marked "IN 09/02/26." The sellers changed it two months before closing, so it is about two months old, inside the one-to-three-month rating printed on its frame. It is not the problem.

The gas valve at the furnace is turned off and has a red tag dated 03/04/2026, reading "flue gas spilling at draft hood." That was eight months before the family moved in. The sellers either did not repair it or did not mention it.

The electrical panel has a final-approved sticker from 06/11/2019, permit E19-0412. Unrelated to the furnace, but worth a note.

What the family did. They did not turn the gas valve on "to see if it works," even though the furnace looked fine. Exhaust spilling at the draft hood means combustion gases, which can include carbon monoxide, were coming into the house instead of going up the vent, and nothing about the furnace looking normal says that has changed. They checked that the carbon monoxide alarms in the house worked, ran two electric space heaters plugged directly into wall outlets in the bedrooms, and called an HVAC company the next morning, reading the red tag to the dispatcher word for word and saying it was a no-heat call with a red tag.

What the technician found. A disconnected and corroded section of vent connector between the furnace and the chimney. The technician replaced it, checked that exhaust was going up the vent with the furnace running, and called the gas utility, which in that area wanted to inspect before the tag came off. The utility came the next afternoon, confirmed it, removed the tag and relit the furnace.

What they filed. A photo of each of the four tags, the technician's invoice describing the repair, the utility's paperwork clearing the tag, and the permit number from the panel. They also raised the red tag with their real estate agent, since it predated the sale. See related: Your House Records File and What Goes In It.

What would have changed this. If the red tag had been on the gas meter instead of the furnace, the whole house would have had no gas, including the water heater and range, and the first call would have been to the gas utility. If the tag had been yellow and said "needs repair, not shut off," the furnace would still have been worth having looked at before the season, but it would not have been a do-not-operate situation.

References

• Your gas utility's guidance on red tags and how service is restored in your area
• See related: How to Respond If You Smell Gas in Your Home
• See related: What a Permit Means for You as the Homeowner
• See related: Your House Records File and What Goes In It
• See related: What Your Carbon Monoxide Alarm Is Telling You