Heater not coming on: what to check after months of sitting idle
The first cold morning is when a heater that sat unused all summer shows its problems. Most are settings, not breakdowns. A few are not.
A heater that does nothing on the first cold day is rarely dead. It has been off for months, and something about the setup changed while nobody was watching. Start with the cheap, boring causes.
This guide is about the first start of the season. If the heater ran fine last week and stopped, the guide on a heater that will not turn on fits better.
Is the thermostat actually asking for heat?
Many thermostats keep a summer setting. Check that the mode is on heat, not cool or off, and that the setpoint is a few degrees above the room reading. If the display is blank, replace the batteries first. A programmable model may also have a schedule that tells the heater to wait until evening.
Look at the power and the switch
Heating equipment usually has its own wall switch that looks like a light switch, often near the unit. Someone may have flipped it off in spring. Check the breaker for the heater too. Reset a tripped breaker once. If it trips again, stop and call a licensed technician.
Check the boiler gauge and the shutoff valves
On a hot-water system, find the pressure gauge. A reading near zero after a long idle spell means the system has lost water, and many boilers will not fire in that state. Do not keep adding water to chase the number, because repeated top-ups can hide a leak. Also look at the valves on the pipes near the boiler. A handle that sits across the pipe instead of along it is closed. Open it only if you know it was closed by mistake.
Give it a few minutes before you decide
Modern heaters do not light the moment the thermostat calls. They run through a startup sequence: a fan or pump first, then ignition. That can take a few minutes. A short pause is normal. A repeated cycle that starts and then stops without producing heat is not, and usually points at a safety lockout that a technician should read.
Dust and a dry spell can make the first start smell
Dust that settled on the heating surfaces burns off on the first run and can give off a smell for a short while. That is common and usually fades quickly. A smell of gas is different. Leave the house at once and call your gas utility or 911 from outside. Do not look for the source.
| What you see | Likely cause | Who handles it |
|---|---|---|
| Thermostat blank | Dead batteries or lost power | You |
| Thermostat on cool or off | Summer setting left in place | You |
| Wall switch or breaker off | Switched off in spring | You, once |
| Boiler gauge near zero | Lost water or a leak | Technician |
| Starts, then stops with no heat | Safety lockout | Technician |
What not to do
- Do not open any panel or touch electrical parts inside the heater.
- Do not keep resetting a unit that locks out. Each reset hides the clue the technician needs.
- Do not ignore a carbon monoxide alarm. Get outside and call 911.
Our advice: get it looked at before the cold snap
If the heater has not run since spring, do not wait for the first freezing night to find out. Turn it on on a mild day while you can still wait for an appointment. A licensed technician can check it, and you will not be negotiating a no-heat emergency.
Frequently asked questions
Why won't my heater come on after summer?
The thermostat may still be on a summer setting, a wall switch or breaker may have been turned off, or a hot-water system may have lost pressure while idle. Check those first.
Is it normal for a heater to smell the first time it runs?
A light dusty smell on the first run is common and usually fades. A smell of gas is an emergency: leave the house and call your gas utility or 911.
How long should a heater take to start?
A few minutes is normal, because the fan or pump runs before ignition. If it starts and stops repeatedly without heat, a safety lockout is likely and a technician should check it.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.