No heat at all
Thermostat is on and calling for heat, but the furnace won't fire. Could be a bad ignitor, flame sensor, gas valve, or control board. Don't wait — Ohio winters are no joke.
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Troubleshooting Guide · Marion, Ohio
Before you call for service, check these common fixes. Most thermostat problems have a simple solution you can handle in under 15 minutes.
6-step guide
Work through these steps in order. Each one takes just a minute or two and fixes the most common thermostat problems Marion homeowners run into.
Is the thermostat screen blank? The unit may have lost power. Check that your HVAC system's power switch (usually on or near the furnace — looks like a regular light switch) is in the ON position. Then check your circuit breaker panel — look for a tripped breaker labeled "HVAC" or "Furnace."
If the breaker keeps tripping, stop here and call PJ's — you may have an electrical issue.
This is the #1 fix for a dead thermostat. Most wall thermostats use AA or AAA batteries that last 1–2 years. Pop the face off (it usually pulls straight out or has a release tab at the bottom), swap in fresh batteries, and snap it back on.
Tip: Even hardwired thermostats often have backup batteries. If your display flickers or shows a low-battery icon, replace them.
It sounds obvious, but we see this all the time: the thermostat is set to OFF, FAN ONLY, or the wrong mode for the season. Make sure it's set to HEAT (winter) or COOL (summer). Then set the target temperature at least 3–5°F above (heat) or below (cool) the current room reading to trigger the system.
Also check any programmed schedules — a scheduled setback (like "Away" mode) might be overriding your manual setting.
Turn the furnace/AC power switch OFF, wait 30 seconds, then turn it back ON. This clears minor electronic glitches in both the thermostat and the HVAC control board. For a smart thermostat (Nest, Ecobee), you can also do a soft restart from the settings menu.
After a reset, give the system 2–3 minutes before expecting it to kick on. Most systems have a built-in delay to protect the compressor.
A clogged air filter is the most common reason a furnace or AC shuts itself off. The system overheats (or freezes up), trips a safety switch, and stops running. Pull the filter out and hold it up to a light — if you can't see through it, replace it. Standard 1" filters should be changed every 1–3 months.
If you don't know where your filter is: most are in a slot between the return air duct and the furnace, or behind a large return vent on a wall or ceiling.
Dust inside the thermostat can throw off the temperature sensor or interfere with connections. Gently remove the faceplate and use a soft brush or canned air to clear dust from the interior. For older mechanical (dial-type) thermostats, also make sure the unit is level on the wall — a tilted mercury switch won't read correctly.
Know the signs
If you've worked through all 6 steps and your system still isn't running right, the problem is likely deeper than the thermostat. Here's when it's time to call PJ's.
Thermostat is on and calling for heat, but the furnace won't fire. Could be a bad ignitor, flame sensor, gas valve, or control board. Don't wait — Ohio winters are no joke.
Call nowA breaker that trips repeatedly when the HVAC runs usually means a short circuit, failing motor, or overloaded circuit. This is a safety issue — don't keep resetting it.
Furnace or AC turns on for a few minutes, shuts off, then repeats. After ruling out a dirty filter, this points to a faulty flame sensor, refrigerant issue, or oversized equipment.
If your thermostat is 10+ years old or still uses a mercury switch, a modern programmable or smart thermostat can cut energy costs 10–15%. PJ's installs and configures all major brands.
Common questions
A blank thermostat display usually means dead batteries, a tripped circuit breaker, or a blown fuse. Replace the batteries first — that fixes the problem about 70% of the time. If the display is still blank, check your electrical panel and the furnace power switch.
This is called short-cycling and it's usually caused by a dirty air filter restricting airflow. The furnace overheats, shuts off for safety, cools down, and repeats. Replace the filter first. If short-cycling continues, the problem may be a faulty flame sensor or oversized unit — call PJ's at (740) 382-6141.
The sensor may be reading incorrectly due to its location (near a window, vent, or in direct sunlight), dust buildup inside the unit, or age. Try cleaning the thermostat interior. If the problem persists, a new programmable thermostat ($150–$300 installed) will solve it and likely lower your energy bills.
A smart thermostat (Nest, Ecobee, Honeywell Home) can save 10–15% on heating and cooling bills by learning your schedule. PJ's installs and configures smart thermostats — we'll make sure it's compatible with your system and set it up correctly. Call (740) 382-6141 for a quote.
A thermostat replacement in Marion typically costs $150–$300 including installation, depending on the model. Smart thermostats run $200–$400 installed. PJ's provides a clear estimate before any work — no surprises.
Related services
Won't start, strange noises, no heat? We diagnose and repair all furnace brands — often same day.
Not cooling? Frozen coil? Refrigerant leak? We'll get your air conditioning running right.
Annual maintenance catches small problems (like thermostat drift) before they become expensive repairs.
What our customers say
★★★★★“My thermostat was acting up and I couldn’t figure it out. PJ’s came out, diagnosed a wiring issue in 10 minutes, and had it fixed within the hour. Fair price, honest work.”
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Tips and guides from our team:
★★★★★“PJ’s installed a Nest thermostat for us and showed us how to use it. Our gas bill dropped by about $30 a month. Should have done it years ago.”
If you've tried the steps above and your HVAC system still isn't cooperating, fill out the form and we'll call you back — usually within the hour.
(740) 382-6141