🌡️Thermostat

B07

Nest · Nest Learning Thermostat (3rd Gen)

Nest Nest Learning Thermostat (3rd Gen) B07 Error Fix: System Running Too Long Alert

Thermostat sends a notification that the HVAC system has been running for an unusually long time without reaching the set temperature. This 'Heads Up' alert indicates declining system performance. Common causes: dirty air filter, low refrigerant, duct leaks, extreme outdoor temperatures exceeding system capacity, or a set temperature that's unrealistic for conditions. Check and replace the air filter, ensure all vents are open and unobstructed, and verify the outdoor unit coils are clean.

Medium severity2 fixes available

Quick Answer

Error B07 on the Nest Nest Learning Thermostat (3rd Gen) means: System Running Too Long Alert. The top-ranked community fix is “Inspect and Repair Duct Leaks and Check Refrigerant Levels” (medium difficulty, ~90 min, DIY cost: $0-$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: $200-$350.

Other Nest Models with Error B07

Nest Learning Thermostat (4th Gen)

thermostat · 2 fixes

Nest Thermostat (2020)

thermostat · 2 fixes

Nest Thermostat E

thermostat · 2 fixes

Other Nest Nest Learning Thermostat (3rd 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

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 Learning Thermostat (3rd Gen) Error B07

What does error code B07 mean on a Nest Nest Learning Thermostat (3rd Gen)?

Error code B07 on the Nest Nest Learning Thermostat (3rd Gen) means: System Running Too Long Alert. Thermostat sends a notification that the HVAC system has been running for an unusually long time without reaching the set temperature. This 'Heads Up' alert indicates declining system performance. Common causes: dirty air filter, low refrigerant, duct leaks, extreme outdoor temperatures exceeding system capacity, or a set temperature that's unrealistic for conditions. Check and replace the air filter, ensure all vents are open and unobstructed, and verify the outdoor unit coils are clean.

How do I fix error code B07 on my Nest Nest Learning Thermostat (3rd Gen)?

The most successful fix is "Inspect and Repair Duct Leaks and Check Refrigerant Levels" (medium difficulty, ~90 minutes). Estimated DIY cost: $0-$20. HomeMD has 2 community-ranked fixes for this error.

Is error code B07 on a Nest Nest Learning Thermostat (3rd Gen) serious?

This error is rated medium severity. It should be addressed soon, but your appliance may still function in a limited capacity.

Can I fix Nest Nest Learning Thermostat (3rd Gen) error B07 myself?

Yes — the top-ranked community fix ("Inspect and Repair Duct Leaks and Check Refrigerant Levels") is rated medium difficulty and takes about 90 minutes. Tools needed: Mastic sealant, metal foil tape, HVAC manifold gauge set, coil cleaner spray, soft brush.

How much does it cost to repair Nest Nest Learning Thermostat (3rd Gen) error B07?

DIY cost: $0-$20. 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 (3rd Gen) have?

The Nest Nest Learning Thermostat (3rd 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 B07 error?

Error code B07 also appears on 3 other Nest models: Nest Learning Thermostat (4th 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 (3rd Gen) have?

The Nest Nest Learning Thermostat (3rd 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)
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 B07 error?

Error code B07 also appears on 3 other Nest models:

Nest Learning Thermostat (4th Gen) (thermostat) · 2 fixes
Nest Thermostat (2020) (thermostat) · 2 fixes
Nest Thermostat E (thermostat) · 2 fixes

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