Why Your Heater is Not Working and What to Do

Phoenix winters are mild compared to most of the country, but when temperatures drop to 35°F at night in January, a heater that's not working is a real problem. If you're a homeowner dealing with a heater that won't turn on, won't produce heat, or keeps shutting off, here's a straightforward troubleshooting guide from the Sapper HVAC team.

Start Here: Quick Checks Before Calling

Before calling for a heating repair visit, run through these basic checks — they resolve a surprising number of "heater not working" calls:

• Check the thermostat. Is it set to "Heat" mode? Is the temperature set above the current room temp? Are the batteries dead?
• Check the air filter. A severely clogged filter can cause the system to overheat and shut down as a safety measure.
• Check the circuit breaker. The furnace or air handler may have a tripped breaker. Reset it once — if it trips again, call a technician.
• Check the furnace switch. Many furnaces have a wall switch that looks like a light switch nearby. Make sure it's in the ON position.
• Check the gas supply. If you have a gas furnace, confirm the gas valve to the unit is open (handle parallel to the pipe = open).

Common Reasons Your Heater Is Not Working

1. Faulty Ignitor or Pilot Light

Gas furnaces use either a hot surface ignitor or a standing pilot light to ignite the burners. A failed ignitor is one of the most common heater not working complaints in Phoenix. The furnace will try to start, fail to ignite, and lock out. A technician can test and replace the ignitor quickly — it's a relatively inexpensive repair.

2. Dirty or Clogged Air Filter

A clogged filter restricts airflow over the heat exchanger. The system overheats and the high-limit safety switch kicks in to protect the unit — which shuts the heat off. Replace the filter and reset the system. If it keeps happening, you may have an airflow problem that needs professional attention.

3. Dead Thermostat

Thermostats — especially battery-powered ones — can fail unexpectedly. If your thermostat screen is blank or unresponsive, replace the batteries first. If that doesn't fix it, the thermostat itself may need to be replaced.

4. Heat Pump in Defrost Mode

If your home has a heat pump and it seems to be blowing cool air occasionally, it may be in defrost mode — a normal cycle where the system briefly runs in reverse to melt any ice buildup on the outdoor coil. This is normal and should last no more than 10 minutes. If the heat pump runs in defrost mode constantly or never blows warm air, call Sapper HVAC.

5. Cracked Heat Exchanger

This is the most serious issue on this list. A cracked heat exchanger in a gas furnace can allow combustion gases — including carbon monoxide — to mix with the air in your home. If a technician finds a cracked heat exchanger, the system must be shut down immediately. This is a safety emergency.

6. Gas Supply Problem

If other gas appliances in your home (stove, water heater) are also not working, the issue may be with your gas supply — contact your utility provider. If only the furnace is affected, the gas valve to the unit may be stuck or failing.

When to Call Sapper HVAC for Heating Repair

Call us immediately if:

• Your carbon monoxide detector is alarming
• You smell gas near the furnace
• The heater makes loud banging or popping noises
• The breaker trips repeatedly after reset
• The system has been professionally diagnosed with a cracked heat exchanger

Sapper HVAC provides same-day heating repair across Phoenix Metro. We serve Chandler, Gilbert, Mesa, Scottsdale, Tempe, Glendale, Peoria, Surprise, and surrounding areas.

Frequently Asked Questions

Why does my heater turn on but not blow warm air?

The most common causes are a failed ignitor (gas furnace), a malfunctioning reversing valve (heat pump), or a dirty evaporator coil causing the system to blow air before reaching operating temperature. A technician can diagnose this quickly.

Is it safe to run my heater if I smell something burning?

A brief burning smell the first time you use your furnace in the season is normal — it's dust burning off the heat exchanger. If the smell is persistent, smells like burning plastic or rubber, or comes with smoke, shut the system off and call Sapper HVAC immediately.

How much does heating repair cost in Phoenix?

Most heating repairs range from $150–$600. Ignitor replacement runs $150–$300. Capacitor replacement is $150–$250. More complex repairs involving gas valves or heat exchangers can be higher. Sapper HVAC provides upfront pricing before any work begins.