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A10

Nest · Nest Thermostat (2020)

Nest Nest Thermostat (2020) A10 Error Fix: Blown Fuse at Furnace Control Board

The 3-5 amp fuse on the furnace or air handler control board has blown, cutting 24VAC power to the thermostat and all HVAC controls. This is the #1 cause of Nest thermostat power loss after installation. Most commonly caused by momentarily shorting the R and C wires together during thermostat installation. Replace the fuse on the furnace control board (typically a 3A or 5A automotive-style mini fuse). Check for wiring shorts before powering back on.

critical2 fixes available

Quick Answer

Error A10 on the Nest Nest Thermostat (2020) means: Blown Fuse at Furnace Control Board. The top-ranked community fix is “Test and Replace Furnace Control Board Fuse and Inspect Wiring for Shorts” (medium difficulty, ~45 min, DIY cost: $10-$20). 2 community-ranked fixes available below.

Published February 2026 · 2 fixes · thermostat

Content is based on manufacturer service documentation, community repair experience, and OEM technical bulletins. Always verify with your owner's manual.Learn about our editorial standards.

When to Call a Professional

While many thermostat repairs can be done safely at home, consider hiring a qualified technician if:

The repair involves electrical wiring, gas lines, or refrigerant
You've tried the top-ranked fix and the error persists
You smell gas, see sparking, or notice water leaking
The repair requires specialized tools you don't have
Your appliance is still under manufacturer warranty

Average professional repair cost for this issue: $120-$180.

Other Nest Models with Error A10

Nest Learning Thermostat (3rd Gen)

thermostat · 2 fixes

Nest Learning Thermostat (4th Gen)

thermostat · 2 fixes

Nest Thermostat E

thermostat · 2 fixes

Other Nest Nest Thermostat (2020) Error Codes

A01

No Power / Low Battery

2 fixes

A02

'Delayed' Message on Display

2 fixes

A03

No Power to Rh/Rc Wire

2 fixes

A04

W1/W2 Heating Wire Not Detected

2 fixes

A05

Y1/Y2 Cooling Wire Not Detected

2 fixes

A06

G (Fan) Wire Not Detected

2 fixes

A07

O/B (Heat Pump Reversing Valve) Wire Not Detected

2 fixes

A08

Wiring Error / Incompatible Wiring

2 fixes

People Also Ask About Nest Nest Thermostat (2020) Error A10

What does error code A10 mean on a Nest Nest Thermostat (2020)?

Error code A10 on the Nest Nest Thermostat (2020) means: Blown Fuse at Furnace Control Board. The 3-5 amp fuse on the furnace or air handler control board has blown, cutting 24VAC power to the thermostat and all HVAC controls. This is the #1 cause of Nest thermostat power loss after installation. Most commonly caused by momentarily shorting the R and C wires together during thermostat installation. Replace the fuse on the furnace control board (typically a 3A or 5A automotive-style mini fuse). Check for wiring shorts before powering back on.

How do I fix error code A10 on my Nest Nest Thermostat (2020)?

The most successful fix is "Test and Replace Furnace Control Board Fuse and Inspect Wiring for Shorts" (medium difficulty, ~45 minutes). Estimated DIY cost: $10-$20. HomeMD has 2 community-ranked fixes for this error.

Is error code A10 on a Nest Nest Thermostat (2020) serious?

This error is rated critical severity. It is generally not urgent and can often be resolved with a simple DIY fix.

Can I fix Nest Nest Thermostat (2020) error A10 myself?

Yes — the top-ranked community fix ("Test and Replace Furnace Control Board Fuse and Inspect Wiring for Shorts") is rated medium difficulty and takes about 45 minutes. Tools needed: T20 Torx screwdriver, Multimeter, Wire strippers, Needle-nose pliers.

How much does it cost to repair Nest Nest Thermostat (2020) error A10?

DIY cost: $10-$20. Professional repair typically costs $120-$180. Many homeowners save money by trying the top-ranked community fix first.

What other error codes does the Nest Nest Thermostat (2020) have?

The Nest Nest Thermostat (2020) has 8 other known error codes, including: A01 (No Power / Low Battery), A02 ('Delayed' Message on Display), A03 (No Power to Rh/Rc Wire), A04 (W1/W2 Heating Wire Not Detected), A05 (Y1/Y2 Cooling Wire Not Detected), and 3 more.

Which other Nest models have the A10 error?

Error code A10 also appears on 3 other Nest models: Nest Learning Thermostat (3rd Gen), Nest Learning Thermostat (4th Gen), Nest Thermostat E. The fix may vary by model, so check each model's specific page for tailored repair steps.

What other error codes does the Nest Nest Thermostat (2020) have?

The Nest Nest Thermostat (2020) has 8 other known error codes:

A01 — No Power / Low Battery (2 fixes)
A02 — 'Delayed' Message on Display (2 fixes)
A03 — No Power to Rh/Rc Wire (2 fixes)
A04 — W1/W2 Heating Wire Not Detected (2 fixes)
A05 — Y1/Y2 Cooling Wire Not Detected (2 fixes)
A06 — G (Fan) Wire Not Detected (2 fixes)
A07 — O/B (Heat Pump Reversing Valve) Wire Not Detected (2 fixes)
A08 — Wiring Error / Incompatible Wiring (2 fixes)

Which other Nest models have the A10 error?

Error code A10 also appears on 3 other Nest models:

Nest Learning Thermostat (3rd Gen) (thermostat) · 2 fixes
Nest Learning Thermostat (4th Gen) (thermostat) · 2 fixes
Nest Thermostat E (thermostat) · 2 fixes

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