Heat not kicking on: what to check before you call
The thermostat clicks and the house stays cold. Often the heater is waiting on a setting, a switch or its own startup sequence.
If the heat is not kicking on, the problem is usually upstream of the heater itself. The thermostat, a switch or a short delay can each keep it from starting. Check those in order.
Skip any step that asks you to open the heater. None of these checks does.
Start at the thermostat
Make sure the mode is on heat and the setpoint sits a few degrees above the room temperature. A blank screen means dead batteries or lost power. A schedule may also be holding the heat back until later in the day. Hold the setpoint up for a few minutes and listen for a click from the thermostat or a hum from the heater.
Check the wall switch and the breaker
Most heating equipment has a switch that looks like a light switch, often on or near the unit. It is easy to flip off by accident. Check the breaker as well and reset a tripped one once. If it trips again, stop and call a licensed technician.
Give it time to start up
A heater does not light the instant the thermostat calls. A fan or pump runs first, then ignition follows. That can take a few minutes. A pause is normal. A unit that starts and then shuts down again with no heat has probably locked out for safety, and that needs a technician to read it.
On a boiler, read the gauge
A hot-water system has a pressure gauge. A reading near zero means the system has lost water, and many boilers will not fire in that state. Do not keep topping it up to chase the number. Repeated refills can hide a leak. If the gauge stays low, call a professional.
Check that your fuel is available
If your home uses a fuel tank, make sure it is not empty. On gas, other gas appliances such as the stove can tell you if the supply is on. If you ever smell gas, leave the house at once and call your gas utility or 911 from outside. Do not look for the source and do not touch switches on the way out.
What not to do
- Do not open the heater's panels or touch the wiring.
- Do not keep pressing the reset button. Each reset hides the clue a technician needs, and repeated tries can be unsafe.
- Do not ignore a carbon monoxide alarm. Get outside and call 911.
Our advice: do the five-minute check, then stop
If the thermostat, switch, breaker, gauge and startup delay all look right, you are done. Anything beyond that is licensed work. Calling early on a mild day beats calling during a freeze, when every technician is booked.
Frequently asked questions
Why is my heat not kicking on when the thermostat is set?
The mode may be wrong, a wall switch or breaker may be off, or the heater may be in its startup delay. A boiler can also be blocked by low water pressure.
How long should it take for heat to kick on?
A few minutes is normal, since a fan or pump runs before ignition. If it starts and stops repeatedly without heat, a safety lockout is likely.
What should I do if I smell gas when the heat won't start?
Leave the house at once and call your gas utility or 911 from outside. Do not look for the source or try to fix 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.