No Heat? 10 Things to Check Before You Call for Service
One of the most common reasons we get dispatched for a no-heat call in New Hampshire turns out to be a $4 set of thermostat batteries. The service call costs many times more than the batteries do. That is what makes them, jokingly, the most expensive batteries a homeowner ever buys.
Before you pick up the phone in the middle of a cold night, run through the quick checklist below. Most no-heat issues are solved by something a homeowner can fix in under two minutes.
1. Check the thermostat
- Battery-powered thermostats: if the screen is blank or dim, or the system is unresponsive, replace the batteries. Most thermostats take two AA or two AAA alkaline batteries behind the faceplate.
- Mode and setpoint: confirm the thermostat is set to Heat (not Off or Cool), and that the setpoint is above the current room temperature.
- Schedule overrides: if your thermostat is programmable or smart, make sure a vacation hold or away schedule has not put it in setback mode.
Most modern smart thermostats (Ecobee, Nest, Honeywell Home) are powered by the system's low-voltage wiring instead of batteries, so this check applies primarily to older or basic programmable models.
2. Check the furnace switch
Most furnaces and boilers have a wall switch within sight of the equipment, often at the top of the basement stairs or on a beam above the unit. It looks like a regular light switch and is sometimes mistaken for one.
- Make sure the switch is in the On position.
- If you have recently had work done in the basement, or anyone has changed a light bulb nearby, it is worth confirming nothing got flipped by accident.
3. Check the circuit breaker
Go to your electrical panel and look for the breaker labeled for the furnace, boiler, or air handler.
- If it is in the middle "tripped" position, flip it fully to Off and then back to On.
- If it trips again immediately, leave it off and call for service. A breaker that will not reset usually indicates a real electrical problem.
4. Check the air filter
A severely clogged filter can cause a furnace to overheat and shut down on a safety limit, or a heat pump indoor coil to ice over. If your filter is dark gray and dust-coated, pull it out and try the system without the filter for the moment, then replace the filter as soon as possible.
5. For oil heat: check the oil tank level
If you heat with oil, the most obvious cause of a sudden no-heat is an empty tank. Tap the side of the tank or check the gauge. If the tank is dry, call your oil supplier for an emergency delivery. After the tank is refilled, the burner will likely need to be primed before it will fire. Most homeowners are not equipped to bleed an oil burner safely, so a service call is usually warranted after a run-out.
6. For propane: check the regulator and tank
If you heat with propane, confirm the tank is not empty and the regulator is not buried in snow or ice. Outdoor propane regulators can freeze over and stop the flow of gas during cold snaps. Clear any snow or ice gently with a broom, never with a hammer or sharp tool.
7. For natural gas: check that gas service is on
If a gas appliance (stove, water heater) elsewhere in the home is also out, your gas service may be interrupted. Call your gas utility, not us, in that case.
8. For heat pumps: clear the outdoor unit
- If the outdoor unit is buried in snow, clear 18 to 24 inches of space around it gently. Do not chip ice with sharp tools.
- Heat pumps run periodic defrost cycles. A little frost on the unit is normal. A unit completely glazed over with thick ice is not.
9. For high-efficiency furnaces and boilers: check the venting
Many modern systems use PVC venting that exits through the side of the home. Snow drifts can block the intake or exhaust and cause the system to shut down on a safety. Walk around the house and visually confirm both vents are clear of snow.
10. Reset and listen
If everything above looks fine, try turning the thermostat down well below the room temperature for 30 seconds, then back up to your setpoint. Listen for the system to start its sequence. Many systems take 1 to 3 minutes from a call for heat before the burner or compressor actually fires.
When to stop troubleshooting and call
If you smell gas, do not keep troubleshooting. Leave the home immediately and do not operate any light switches, phones, or anything that could create a spark while inside. Call 911 and your gas utility from outside the home or from a neighbor's phone, and do not re-enter until emergency responders have cleared the home. Only then call us.
If you have worked through the checklist and the system still will not run, or if you see soot, hear unusual noises, or see error codes on the equipment, stop and call.
For 24/7 emergency service in southern New Hampshire, call A.J. LeBlanc Heating at 603-623-0412. Serving NH families since 1928.
Frequently Asked Questions
How often should I change thermostat batteries?
Once a year, ideally before the heating season. Many homeowners change them at the same time they replace smoke detector batteries.
What does it mean if my furnace flashes an error code?
Most modern furnaces have a small LED that blinks a numeric error code when there is a fault. The legend is usually on a sticker inside the access panel. Note the code and share it with the technician when you call. It often shortens the diagnostic time.
My circuit breaker keeps tripping. Should I keep resetting it?
No. A breaker that trips repeatedly is doing its job and telling you something is wrong. Leave it off and call for service.
I ran out of oil. What do I need to do?
Call your oil supplier for an emergency delivery. After the delivery, the burner will usually need to be primed by a technician. Do not attempt to bleed the burner yourself unless you are trained.
Is there a service-call charge if you arrive and the problem is something simple?
Yes. Whether the fix is a battery or a major repair, the diagnostic visit itself is billable. That is why the homeowner checklist above is worth doing first.