Ecobee Smart Thermostat Firmware 4.9.227 Triggers HVAC_FAULT_E5 on Heat Pumps
Dated: March 2, 2026 — Ecobee firmware 4.9.227
A recent Ecobee firmware update is reportedly throwing a reversing valve fault on heat pump systems running auxiliary electric strip heat, especially during defrost cycles where the reversing valve toggles through the O/B terminal. Owners describe the fault locking out the compressor briefly and dropping the system to backup heat, which can spike electric bills. Until Ecobee ships a patch, the working fix is to raise the auxiliary balance point in Installation Settings and confirm the reversing valve polarity matches your outdoor unit.
- Affected software: A recent Ecobee thermostat firmware update
- Symptom: Reversing valve fault code appearing in Equipment History
- Affected hardware: Air-source heat pumps with O or B reversing valve wiring, especially dual-fuel systems
- Consumer impact: Compressor lockouts and extended bursts of electric strip heat during cold snaps
- Ecobee response: Patch tracked, no consumer rollback path available
Purpose-built diagram for this article — Ecobee Smart Thermostat Firmware 4.9.227 Triggers HVAC_FAULT_E5 on Heat Pumps.
The diagram above traces the signal path where the firmware misreads the reversing valve state. The updated defrost logic watches the O/B terminal during a forced Y1 call, and when the compressor contactor chatters during the physical valve shift, the firmware can tag that brief state mismatch as a valve fault rather than a normal defrost transition. That mislabel is what generates the fault code and drops the system into auxiliary heat.
What does the new reversing valve fault actually mean after the update?
Ecobee uses internal codes to flag reversing valve state mismatches, which occur when the commanded mode disagrees with the state sensed on the O/B terminal. Owners report that the updated firmware is noticeably less tolerant of brief disagreements during defrost than prior versions, which is why so many hit the fault on the same day the update landed.
If you open your thermostat’s Equipment History (Menu → About → Equipment), you’ll see fault rows clustered around defrost initiations rather than scattered randomly. Ecobee’s public HVAC error codes reference still documents the family of reversing valve sensing faults, but the article has not been updated to reflect the tighter sensing windows in the current firmware.
See also another Ecobee firmware issue.
Category breakdown — E5 Fault Breakdown.
The breakdown image shows the three conditions the firmware checks simultaneously: commanded mode, O/B terminal state, and compressor current sense. When any of the three disagree for more than a handful of seconds, the new firmware aborts the cycle and posts the fault. Older firmware looked primarily at the first two signals, which is why the same wiring that worked fine previously now produces faults during defrost cycles in cold weather.
The practical effect is a compressor lockout. During that window, the thermostat falls back to W1 or W2 auxiliary heat, typically a 10 kW electric strip, and your kilowatt-hours jump accordingly. Homes in climates where the outdoor unit defrosts every 35 to 45 minutes will hit the lockout repeatedly in a 24-hour period. Utility bills for affected weeks have come in noticeably higher than normal for affected households, which is why complaint volume on r/ecobee and the Ecobee community forums climbed within days of the update.
The Reddit snapshot captures the pattern owners keep describing: the fault appears within hours of the update completing, it correlates almost perfectly with outdoor temperatures in the 25 to 40°F range where defrost cycles are most frequent, and clearing the code manually accomplishes nothing because the next defrost immediately re-triggers it. Some utility customers in the Northeast also reported their smart-thermostat demand-response programs flagged their homes because the aux heat runtime tripped the program’s eligibility threshold for the month.
Which heat pump configurations are most likely to throw the fault?
Three configurations are showing up repeatedly in the field reports. The first is any dual-fuel setup where a heat pump is paired with a gas furnace and the ecobee controls the switchover via outdoor temperature. The second is single-stage heat pumps with electric auxiliary strip heat wired to W1. The third, and most stubborn, is variable-capacity or communicating heat pumps using the Ecobee’s standard 24V interface rather than the manufacturer’s proprietary control board.
Dual-fuel systems break because the new firmware treats the gas stage as a hard backup and expects the reversing valve to be deenergized during that stage. If your valve is wired for O, which energizes in cooling, versus B, which energizes in heating, and your furnace board loops Y1 back through a relay, the ecobee can see the valve energized during what it thinks should be a gas-only call and flags the fault. This is the single most common variant of the issue in recent reports.
For more on this, see another botched firmware rollout.
Electric strip systems fail during defrost because the new code assumes the reversing valve will settle within a few seconds of a commanded transition. Older American Standard, Rheem, and Goodman outdoor units take 8 to 12 seconds to physically shift the valve, especially in cold weather when the refrigerant is sluggish and the pilot solenoid has more work to do. Those extra seconds of disagreement between commanded state and sensed state are enough to trip the new firmware every cycle.
Communicating units fail for a different reason entirely. When a Carrier Infinity, Trane XV, or Bosch IDS outdoor unit negotiates capacity over its proprietary bus, the 24V signals the ecobee sees on Y1 and Y2 don’t map cleanly to actual compressor runtime. The thermostat’s current-sense check times out waiting for a signature that never comes, and the fault fires even though the system is operating correctly. Owners of these systems are the most frustrated group because even the published workarounds don’t fully resolve the fault for them.
Differences at a glance — Ecobee FW 4.9.227 E5 Fault Comparison.
The comparison image lays out which systems Ecobee owners have confirmed are hitting the fault versus which ones are running the new firmware cleanly. Worth noting: geothermal ground-source heat pumps are conspicuously absent from the fault reports because their valves don’t defrost in the same way, and straight air-conditioning-only installs aren’t affected at all since they never reverse. Ductless mini-split head units running behind a third-party 24V adapter are hitting the fault almost universally.
How do you stop the fault loop until Ecobee ships a patch?
There is no official rollback button. Ecobee’s firmware update path is forward-only for consumers, which is why this has turned into a real problem rather than a one-click revert. Three workarounds are working reliably in the field.
Workaround 1: lower the aux heat balance point. Go to Menu → Settings → Installation Settings → Equipment → Heat Pump, and lower the “Compressor to Aux Heat” balance point (for example, to –20°F). This prevents the firmware from bringing auxiliary heat online during a defrost cycle, which breaks the fault loop because the lockout has nothing to fall back to and simply waits for the compressor to restart. You’ll give up some deep-cold-weather capacity, so it’s a short-term bridge rather than a permanent fix.
I wrote about rethinking your smart home stack if you want to dig deeper.
Workaround 2: reversing valve polarity check. In Installation Settings → Equipment → Reversing Valve, verify the O/B setting matches your outdoor unit. O means the valve is energized in cooling (Carrier, Trane, most American brands). B means energized in heating (Rheem, some Lennox models, older Goodman). A mismatch here was benign on prior firmware but causes nearly instant faults on the current build. A meaningful share of the complaints on the Ecobee community board trace back to a silent polarity error that the old firmware forgave and the new firmware doesn’t.
Workaround 3: extend the defrost dwell. If your outdoor unit has a field-adjustable defrost board, increase the defrost termination time from 30 seconds to 60 seconds. That extra half-minute gives the reversing valve physical time to settle before the ecobee re-reads the O/B state. You’ll need your installer for this adjustment on most units; it’s a DIP switch on some boards, a service menu selection on newer ones, and a solder jumper on a few older Rheem boards that you should not attempt without a tech.
Owners are actively tracking the issue and sharing workarounds on the Ecobee community forum. In the meantime, the combination of workarounds 1 and 2 eliminates the fault for the vast majority of homes reporting it. Some electric utilities have separately raised the demand-response implications of the extended aux-heat runtime, and enrolled customers should check with their utility about how the affected runtime is being treated for program eligibility.
If your system is still throwing the fault after both software workarounds, pull the thermostat off the wall and check that the C wire is landed and carrying a stable 24VAC under load. A handful of reports have traced back to undersized common wires dropping to 20VAC during compressor inrush, which the stricter current-sense timing in the new firmware now catches where the older firmware ignored it. For deeper protocol-level debugging, the ecobee Developer API documentation exposes thermostat equipment state and runtime report endpoints that let you confirm which fault state the thermostat is in programmatically, without pulling the unit off the wall or waiting for the next lockout to watch it happen in person.
If you saw a reversing valve fault appear after a recent firmware update, you are not broken, your HVAC is not broken, and you don’t need a service call. Check your reversing valve polarity, lower the aux balance point, and hold until Ecobee ships a patch. If your electric bill already jumped from a week of strip-heat lockouts, call your utility before the month closes out. Some demand-response programs may credit accounts that got hit by firmware issues, but typically only for customers who flag it before the billing cycle resets.
You might also find similar firmware regression useful.
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