🌡️Thermostat

A07

Nest · Nest Learning Thermostat (4th Gen)

Nest Nest Learning Thermostat (4th Gen) A07 Error Fix: O/B (Heat Pump Reversing Valve) Wire Not Detected

Thermostat cannot detect the O/B wire that controls the heat pump reversing valve. The heat pump may be stuck in one mode — heating only or cooling only. This code only applies to heat pump systems. Check the O/B terminal on the thermostat base and at the air handler. Verify the reversing valve solenoid has continuity. Some systems use O (energize on cool) while others use B (energize on heat) — ensure the correct setting in Equipment setup.

High severity2 fixes available✨ Free fix available

Quick Answer

Error A07 on the Nest Nest Learning Thermostat (4th Gen) means: O/B (Heat Pump Reversing Valve) Wire Not Detected. The top-ranked community fix is “Test and Replace Heat Pump Reversing Valve Solenoid” (hard difficulty, ~60 min, DIY cost: $15-$30). 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:

This is a high severity error — continued use may cause damage or a safety hazard
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: $200-$350.

Other Nest Models with Error A07

Nest Learning Thermostat (3rd Gen)

thermostat · 2 fixes

Nest Thermostat (2020)

thermostat · 2 fixes

Nest Thermostat E

thermostat · 2 fixes

Other Nest Nest Learning Thermostat (4th Gen) 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

A08

Wiring Error / Incompatible Wiring

2 fixes

A09

System Not Responding / No Equipment Detected

2 fixes

People Also Ask About Nest Nest Learning Thermostat (4th Gen) Error A07

What does error code A07 mean on a Nest Nest Learning Thermostat (4th Gen)?

Error code A07 on the Nest Nest Learning Thermostat (4th Gen) means: O/B (Heat Pump Reversing Valve) Wire Not Detected. Thermostat cannot detect the O/B wire that controls the heat pump reversing valve. The heat pump may be stuck in one mode — heating only or cooling only. This code only applies to heat pump systems. Check the O/B terminal on the thermostat base and at the air handler. Verify the reversing valve solenoid has continuity. Some systems use O (energize on cool) while others use B (energize on heat) — ensure the correct setting in Equipment setup.

How do I fix error code A07 on my Nest Nest Learning Thermostat (4th Gen)?

The most successful fix is "Test and Replace Heat Pump Reversing Valve Solenoid" (hard difficulty, ~60 minutes). Estimated DIY cost: $15-$30. HomeMD has 2 community-ranked fixes for this error.

Is error code A07 on a Nest Nest Learning Thermostat (4th Gen) serious?

This error is rated high severity. You should address it promptly — continued use could cause damage or safety concerns.

Can I fix Nest Nest Learning Thermostat (4th Gen) error A07 myself?

Yes — the top-ranked community fix ("Test and Replace Heat Pump Reversing Valve Solenoid") is rated hard difficulty and takes about 60 minutes. Tools needed: Multimeter, Nut driver set, Phillips screwdriver.

How much does it cost to repair Nest Nest Learning Thermostat (4th Gen) error A07?

DIY cost: $15-$30. Professional repair typically costs $200-$350. Many homeowners save money by trying the top-ranked community fix first.

What other error codes does the Nest Nest Learning Thermostat (4th Gen) have?

The Nest Nest Learning Thermostat (4th Gen) 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 A07 error?

Error code A07 also appears on 3 other Nest models: Nest Learning Thermostat (3rd Gen), Nest Thermostat (2020), 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 Learning Thermostat (4th Gen) have?

The Nest Nest Learning Thermostat (4th Gen) 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)
A08 — Wiring Error / Incompatible Wiring (2 fixes)
A09 — System Not Responding / No Equipment Detected (2 fixes)

Which other Nest models have the A07 error?

Error code A07 also appears on 3 other Nest models:

Nest Learning Thermostat (3rd Gen) (thermostat) · 2 fixes
Nest Thermostat (2020) (thermostat) · 2 fixes
Nest Thermostat E (thermostat) · 2 fixes

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