Nest Nest Learning Thermostat (3rd Gen) B06 Error Fix: Emergency Heat Mode Stuck On

Error code B06 on the Nest Nest Learning Thermostat (3rd Gen) means: Emergency Heat Mode Stuck On. Thermostat is locked in Emergency Heat mode, bypassing the heat pump entirely and using only backup electric heat strips. This is extremely expensive to operate. Check if Emergency Heat was manually enabled (some users activate it during cold snaps and forget). Go to the thermostat and check if the mode shows 'Emergency Heat' — switch back to 'Heat.' If the thermostat keeps reverting to emergency heat, the heat pump outdoor unit may have a fault that the thermostat detected, triggering automatic fallback.

The most successful fix is "Test and Replace Outdoor Heat Pump Defrost Control Board" (hard difficulty, ~60 minutes). Estimated DIY cost: $10-$20. HomeMD has 2 community-ranked fixes for this error.

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

Yes — the top-ranked community fix ("Test and Replace Outdoor Heat Pump Defrost Control Board") is rated hard difficulty and takes about 60 minutes. Tools needed: T20 Torx screwdriver, multimeter, non-contact voltage tester.

DIY cost: $10-$20. Professional repair typically costs $150-$250. Many homeowners save money by trying the top-ranked community fix first.

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.

Error code B06 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.