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Playbook: Stuck or Failed Actuator
Applies toAHU-0020, AHU-0014, AHU-0015, VAV-0004
Fix complexityOn-site service required
Typical time1–4 h on-site
Typical cost$200–$1,200 (actuator + labor)
Energy impactStuck actuators are a root cause behind multiple high-energy faults: simultaneous heating and cooling (10–30% AHU thermal), economizer failure (0–7% site), leaking coil valves (0.5–5% site in cold climates, EEM-03). Fixing one stuck actuator often resolves 2–5 related fault alarms.

Adapted from HVAC FDD Reference v1.0, Remediation Playbooks (pp. 159–160).

Step 1 — Verify the fault

  1. Plot the command signal vs. position feedback over 24 hours; confirm a persistent gap of more than 10% for more than 30 minutes.
  2. From the BAS, manually command the actuator through its full range (0% → 100% → back). If feedback tracks the command, it was likely a temporary glitch — monitor for recurrence. If feedback stays flat regardless of command, the actuator or linkage has failed.
  3. Check for downstream faults this actuator causes: a stuck heating valve → simultaneous H&C (AHU-0016); a stuck OA damper → economizer failure (AHU-0017).

Step 2 — Remote check (limited options)

  1. Release any manual overrides on the command point.
  2. Check whether BAS auto-tuning or demand-limiting features are restricting the command range.
  3. Pneumatic actuators: check the pneumatic transducer output against the command signal.
  4. Check the controller’s alarm/fault log — some DDC controllers log communication errors or actuator timeout events that pinpoint the failure.

Step 3 — On-site service

  1. At the actuator, check in order: (1) is the linkage still connected — disconnected linkages are the most common cause; (2) is the actuator receiving its control signal (voltage / air pressure at the actuator); (3) manually stroke the valve or damper — does it move freely?
  2. Disconnected linkage: reconnect and tighten ($0–$50).
  3. No signal at the actuator: trace wiring back to the controller; check fuses and breakers.
  4. Signal present but no motion: replace the actuator — small valve actuators $200–$600, large damper actuators $300–$800, multi-section damper banks $500–$1,200.
  5. Valve body seized from corrosion or debris: replace the valve ($500–$2,000).
  6. Normally-open heating coil valves: verify the actuator has a spring return — without it, any power or signal loss opens the valve and creates simultaneous heating and cooling.

Step 4 — Confirm resolution

  1. After repair, command the actuator through its full range from the BAS; verify position feedback tracks within 5%.
  2. The fault should clear immediately.
  3. If this actuator was causing simultaneous H&C or economizer failure, check all downstream fault codes within 24 hours — they should resolve too.