Furnace or boiler not turning on? Before you call, check four things: the thermostat, the power to the system, the furnace filter, and (on a boiler) the pressure gauge. Those cover a good share of no-heat calls, and none of them takes more than a few minutes. If they all check out, or you smell gas, stop there and call a technician.
Key takeaways
- Start at the thermostat: heat mode, a setpoint a few degrees above room temperature, and fresh batteries if the screen is blank.
- Furnaces and boilers each have a service switch that looks like a light switch, plus a breaker. Either one can be the whole problem.
- A clogged furnace filter or a full condensate pump can shut a furnace down on purpose to protect it.
- On a boiler, check whether the whole house is cold or just one zone. One cold zone usually points to a zone valve, a thermostat or air in the line.
- If you smell gas, leave the house and call your gas utility or 911 from outside. Don’t flip switches on the way out.
1. Start at the thermostat
It sounds too simple, but the thermostat is where a lot of no-heat calls end. Check that it’s set to Heat, not Cool or Off. Set it three to five degrees above the current room temperature so it has a reason to call for heat. If the screen is blank or dim, replace the batteries. Smart thermostats can lose their Wi-Fi connection or fall back to an old schedule after a power blip, so look for a hold or schedule setting overriding what you just set.
If you have a boiler with more than one zone, each zone has its own thermostat. Check the one for the cold part of the house.
2. Make sure the system has power
Gas furnaces and boilers need electricity to run the controls, igniter, blower or circulator pump. Look for:
- The service switch. It’s usually on the wall or a nearby post and looks like an ordinary light switch. It’s easy to flip off by mistake when someone reaches for the basement light.
- The emergency shutoff. Many homes have a second switch, often at the top of the basement stairs, sometimes with a red cover plate.
- The breaker. Check the panel for a tripped breaker labeled furnace, boiler or heat. If it trips again after you reset it, leave it off and call. A breaker that keeps tripping is telling you something.
Shore storms knock out power often enough that this is worth planning for. A furnace or boiler won’t run during an outage, even with the gas on. Homeowners who don’t want to go without heat in a winter storm often add a whole-house generator.
3. Furnace checks
- The filter. A badly clogged filter starves the furnace of air. It can overheat and shut itself off on a safety limit. If the filter is gray and caked, replace it and give the system a few minutes. Our post on why the furnace filter matters explains how often to change it.
- The blower door. Most furnaces have a safety switch that keeps the unit off if the front panel isn’t seated. If someone just changed the filter, press the panel firmly back in place.
- The condensate drain. High-efficiency furnaces make water, and a clogged drain or a full condensate pump will stop the furnace. Look for water around the base or a pump reservoir that’s full.
- The status light. Many furnaces have a small light on the control board that blinks a code. Write down the pattern before you call. It helps the technician narrow the problem down before they arrive.
If the furnace runs but the air coming out is cold, that’s a different set of causes. See is my furnace blowing cold air?
4. Boiler checks
Many older Jersey Shore homes heat with a boiler and baseboard or radiators. If yours isn’t heating:
- Whole house or one zone? If every zone is cold, the problem is at the boiler: power, ignition, pressure or the circulator. If only one zone is cold, check that zone’s thermostat first, then suspect a zone valve or air in the line.
- The pressure gauge. The right range for your system is usually on a label near the gauge or in the boiler’s manual. Pressure well below that, or climbing toward the red zone, is a reason to call. So is a relief valve that’s dripping or discharging.
- Gurgling or cold baseboards. Trapped air is common after a repair or at the start of the season. Our guide to bleeding baseboard heat walks through it.
What not to do
- Don’t keep pressing a reset button. On any burner, repeated resets can make a bad situation worse.
- Don’t bypass a safety switch, remove panels you can’t put back, or try to relight a system you’re not familiar with.
- Don’t add water to a boiler unless you know your system’s fill valve and correct pressure.
- If you smell gas, leave the house and call your gas utility or 911 from outside. If a carbon monoxide alarm is sounding, get everyone outside and call 911.
One note for oil heat: Rostron Premium Home Services doesn’t service oil heating equipment. If you’re tired of oil problems, we do oil-to-gas conversions.
When it’s time to call
Call a technician if the checks above don’t bring the heat back, if the breaker keeps tripping, if the furnace shows the same error code again, or if the boiler pressure won’t stay in range. Call right away if you smell gas or something burning.
Most of these breakdowns show up first on the coldest night, when everyone else is calling too. A yearly heating tune-up catches many of them early: flame sensors, condensate drains, controls and pressure all get checked. Members of our Service Membership Program get two maintenance visits a year and move ahead of non-members on emergency calls.
For more on keeping a heating system efficient and running, the U.S. Department of Energy’s Energy Saver Guide has a section on heating maintenance.
No heat right now? Call Rostron Premium Home Services at 732-374-9949 or submit an emergency service request. We service gas furnaces, boilers and heat pumps throughout Monmouth and Ocean County, from our office in Wall Township. You can also read more about our heating emergency service.
