Thermostat Installation, Replacement & Repair in Northern Virginia & Maryland

Thermostat Not Working? Run These Quick Checks First

Before you call, spend two minutes on these. They solve many “thermostat not working” problems:

• Batteries. If your thermostat takes AA or AAA batteries, swap in fresh ones. Low batteries cause blank screens, lost Wi-Fi, and settings that “forget” overnight.
• Breaker. Check your electrical panel for a tripped breaker labeled HVAC, furnace, or air handler. Flip it fully off, then back on.
• Mode and setpoint. Make sure it’s set to HEAT in winter or COOL in summer — and set at least 3 degrees beyond the room temperature. A thermostat set to 72 when the room is already 72 has nothing to do.
• Dust and debris. Pop off the faceplate (gently) and blow out dust from the sensor and contacts. A dusty sensor misreads room temperature.
• Check the furnace switch. Most furnaces have an on/off switch that looks like a light switch — sometimes on a nearby wall. Make sure nobody flipped it off.

If the screen is still blank or the system still won’t respond, the problem is deeper: failed wiring, a bad control board, or a thermostat that has reached the end of its life. That’s a $90 visit, and you’ll know what’s wrong and the price before any work.

Thermostat Repair or Thermostat Replacement: How to Decide

Not every bad thermostat needs replacing. Here’s how to decide:

Usually repairable: loose or corroded wire connections, a failing battery connection, a thermostat that’s reading a few degrees off (calibration), a unit that works but keeps losing Wi-Fi (router/wiring issue, not thermostat failure), or a system that stops responding because the furnace or AC itself tripped a safety.

Usually time to replace: the thermostat is 10–15 years old and non-programmable; the display is dim, flickering, or dead even with new batteries; you have a mercury-bulb thermostat (an upgrade is safer and far more accurate); the thermostat isn’t compatible with your new heat pump or two-stage equipment; or it has already been repaired once and is acting up again.

A “furnace won’t turn on” problem sometimes ends at the thermostat, so the technician diagnoses first. If the thermostat is fine and the equipment is the problem, see furnace repair, AC repair or heat pump repair. Either way, the price is in writing before work starts.

Smart Thermostat Installation

Many homeowners replacing a thermostat today choose a smart model. A smart thermostat learns your schedule, lets you change the temperature from your phone, and adjusts for humidity and weather — and it can lower energy bills because the house stops heating and cooling an empty home.

AVS installs smart thermostats. The job covers checking that your system is compatible (heat pump, dual-fuel, multi-stage, zoning — not every smart thermostat works with every system), checking the wiring, installing and configuring it, connecting it to your Wi-Fi, and walking you through the app before we leave.

Three things to know before buying one yourself:

• Compatibility comes first. Send us the model number before you open the box. Some smart thermostats don’t support certain heat pump or dual-fuel setups, and returning an installed unit is no fun.
• The app setup is half the value. Scheduling, geofencing, and energy reports are what make a smart thermostat smart. We set all of that up with you, not just the wiring.
• Old thermostats may need wiring work. Which brings us to the most common gotcha in this category — the C-wire.

C-Wire and Thermostat Wiring Compatibility

The C-wire (common wire) provides continuous power to a thermostat. Older homes across Fairfax County and Montgomery County often lack one, because old mechanical and battery thermostats never needed it. Smart thermostats do.

No C-wire doesn’t mean no smart thermostat. Depending on your setup, the fix can be running a new wire, installing a common-wire adapter kit at the furnace or air handler, or in some cases repurposing an unused wire already in the wall. The right answer depends on your equipment — the technician checks the furnace control board and the wall wiring and recommends the cleanest fix.

Common wiring issues: missing C-wires, heat-pump wiring with auxiliary heat that a DIY install got wrong, zone-control panels with multiple thermostats fighting each other, and old systems where the wire labels no longer match the colors in the wall. If your system short-cycles, runs constantly, or heats and cools at the same time, wiring is a prime suspect.

Thermostat Replacement Cost

Our AC repair cost guide puts thermostat replacement at $299 – $735. What moves you up or down that range: a basic programmable unit sits at the low end; a smart thermostat with a learning display, room sensors, and Wi-Fi setup sits higher; and homes needing a new wire run, a common-wire adapter, or zoning-panel work add labor time. Whatever your situation, you get a written price before work starts — the $90 visit covers the diagnosis, and there’s never a surcharge for evening, weekend, or holiday appointments.

Why Homeowners Choose AVS for Thermostat Replacement

• Family-owned since 1991: More than 30 years of HVAC service in Northern Virginia and Maryland.
• Seen on ABC7 News: Anil Sareen of AVS Heating and Air Conditioning was interviewed on ABC7 News.
• Licensed in Virginia and Maryland: Virginia HVAC 2705039269A · Maryland HVAC 520714137895 · Maryland Home Improvement 4192876.
• Three local offices: Fairfax, VA · Falls Church, VA · Bethesda, MD.
• 4.8★ on Google: 354 reviews across our three offices.