UrgentDiagnostic guide
Thermostat not working or blank screen
A dead or miscalibrated thermostat is one of the most common reasons a perfectly good A/C or furnace won't run — and often the cheapest fix.
01 / 04Likely causes
What is usually
behind it.
The shortlist of root causes we find on this call. The truck is stocked for most of these.
- 01Dead or low batteries
- 02Tripped circuit breaker for the air handler
- 03Loose wiring at the thermostat terminal block
- 04Failed thermostat control board
- 05HVAC system in lockout due to a fault
- 06Thermostat placed in direct sunlight causing wrong readings
02 / 04Right now
Do this while you wait.
Steps that can save product, prevent damage, and shorten the repair once we are on site.
Do this
- Replace the batteries even if the screen seems bright
- Check the breaker panel for the air handler circuit
- Confirm the thermostat is set to COOL or HEAT (not OFF)
Do not do this
- Do not pull wires off terminals without photographing them first
- Do not assume the thermostat is bad before ruling out the HVAC unit
03 / 04On the truck
What our tech will check.
The diagnostic flow we run on this call. Most are resolved on the first visit.
- 01Test thermostat signal output with a meter
- 02Inspect and re-seat wiring at both the thermostat and the air handler
- 03Check for HVAC fault codes that are preventing operation
- 04Replace the thermostat and program it to your schedule if needed
Fast dispatch
Most calls see a tech in under two hours.
First-visit fix
Common parts on every truck.
Documented
Photos and notes attached to your ticket.
04 / 04Related service
This sits under
our hvac service.
Heating, cooling, and air handling for homes — diagnosed honestly and repaired without the upsell theater.
Related problems
Might also be one of these.
Other failures with similar symptoms or in the same trade.
Service request