HP-0008 — Auxiliary heat active above lockout with compressor running


Status	verified — engine `e2ff2f8`, `cxf:fnv1a128:8917cda230eb3df1fff05a46442b7cf9`, 2026-08-20
Severity	2
Method	rule
Phase	2
Category	EXCESS_CONSUMPTION
Confidence	MEDIUM
Estimation	PROXY_ESTIMATION
G36	—
Clusters	—
Suppresses	—
Suppressed by	—
Related	HP-0001, HP-0002, HP-0007
Playbooks	heat-pump-faults
Source	Winkler and Ramaraj, Field Validation of Air-Source Heat Pumps for Cold Climates, NREL/TP-5500-84745 (2023), Table 5 and note b, p.15 — auxiliary lockout is the maximum OAT for auxiliary operation; observed site values vary; NREL HPXML Data Dictionary v4.0, BackupHeatingLockoutTemperature — backup is disabled above the configured temperature and dual-fuel uses BackupHeatingSwitchoverTemperature; Library-authored executable combination of heating mode, configured OAT lockout, concurrent compressor/auxiliary proof, defrost exclusion, and persistence
Operating states	normal automatic heat-pump heating when the configured strategy prohibits auxiliary heat above its site-specific lockout while the compressor runs

Preconditions (host-enforced): aux_heat_status must independently prove active heat production by an explicitly classified auxiliary electric, gas, or other source; do not bind demand, command echo, availability, crankcase heat, base-pan heat, or defrost heat. The 5 degC placeholder is adoption-blocking: replace it with the installed balance/lockout strategy for climate, tariff, and equipment. mode_command code 1 must mean heating; comp_status must prove the same applicable compressor scope. OAT must be valid and representative. Exclude defrost, emergency heat, compressor failure/lockout, demand response, commissioning, and explicit high-capacity recovery. On dual-fuel equipment instantiate only when simultaneous compressor/fuel operation above the configured switchover is prohibited. Unmet obligations are NO_EVAL, not healthy.

Points: aux_heat_status, oat, mode_command, defrost_status, comp_status

Outputs:

yFault — True after heating mode, above-lockout OAT, concurrent auxiliary/compressor proof, and no defrost persist for sustained_duration
yHeatingMode — Diagnostic sub-condition flag; true when mode_command equals heating_mode_code. False never means NO_EVAL
yAboveLockout — Diagnostic sub-condition flag; true when OAT is strictly above aux_heat_lockout_oat. False never means NO_EVAL
yConcurrentHeat — Diagnostic sub-condition flag; true when auxiliary heat and compressor proofs are both active. False never means NO_EVAL

Parameters:

Name	Default	Unit	CXF path	Description
`heating_mode_code`	1	1	`kHeat.k`	LIBRARY_PRECEDENT host-mapped heating-mode integer. Rebind when the site enumeration differs.
`aux_heat_lockout_oat`	5.0	°C	`aboveLockout.t`	NO_PORTABLE_DEFAULT and adoption-blocking placeholder. Replace with the installed unit’s commissioned auxiliary lockout or dual-fuel switchover strategy; equality is clear.
`sustained_duration`	300.0	s	`persist.delayTime`	ADOPTED_TUNABLE continuous signature duration intended to reject brief staging transitions; commission against the OEM sequence.

Description

This rule detects a proven auxiliary heat source operating concurrently with the heat-pump compressor above the configured outdoor lockout in heating mode, outside defrost. It targets prohibited concurrent operation, not emergency heat, required low-temperature supplementation, or balance-point optimization.

Detection Logic

heating_mode   = mode_command == heating_mode_code
above_lockout  = oat > aux_heat_lockout_oat
concurrent_heat = aux_heat_status AND comp_status
candidate = heating_mode AND above_lockout AND concurrent_heat
            AND NOT defrost_status

yHeatingMode = heating_mode
yAboveLockout = above_lockout
yConcurrentHeat = concurrent_heat
yFault = candidate sustained for sustained_duration

The OAT comparison is strict. Diagnostic outputs are immediate; TrueDelay(delayOnInit=true) applies only to the complete signature. Any false candidate subcondition resets timing and clears a mature alarm.

Possible Diagnoses

Auxiliary lockout or dual-fuel switchover misconfigured or disabled
Staging/thermostat sequence energizes backup heat too early
OAT sensor bias, bad location, stale value, or wrong unit conversion
Auxiliary proof bound to command, availability, or a non-space-heating load
Compressor-capacity fault causing an authorized recovery mode not host-gated
Defrost, emergency, demand-response, or commissioning state omitted from gating

5 °C is not a portable default. It is an adoption-blocking placeholder; the applicable value is the installed balance/lockout or switchover strategy.
Confidence is MEDIUM rather than the brief’s proposed HIGH. Auxiliary role/proof, dual-fuel behavior, site setpoint, and emergency/recovery modes must be established before concurrent operation is avoidable.
Auxiliary semantics are provisional. Brick and 223 provide generic heating/status patterns but no exact auxiliary role; topology and independent proof must identify the real supplemental source.
Defrost is encoded; other exceptions are host gates. Emergency, failure, demand-response, and recovery state semantics are site-specific.
No automatic suppression is added. HP-0007 direction should lead diagnosis, but unexpected compressor proof can leave this concurrent-energy signature valid.
No empirical FPR or TPR is claimed. Current datasets do not expose aligned auxiliary-production proof, defrost state, and the configured site lockout.

Test Vectors

14 scenarios, clock step 60 s over 720 s.

Scenario	Description
`cooling_mode`	Concurrent heat in the cooling code is diagnostically visible but outside the heating-mode candidate.
`heating_below_lockout`	Auxiliary support below the configured lockout is permitted by this rule.
`heating_above_lockout_without_auxiliary`	Compressor heating above lockout is healthy when the auxiliary source is inactive.
`auxiliary_above_lockout_compressor_off`	Auxiliary heat without compressor proof may be emergency operation and is not this concurrent-energy signature.
`concurrent_heat_above_lockout_sustained`	The complete avoidable-energy signature matures only after persistence.
`concurrent_heat_during_defrost`	Defrost explicitly removes the alarm candidate while leaving diagnostic subconditions visible.
`exact_oat_lockout_is_clear`	The exact configured OAT threshold is clear under strict greater-than semantics.
`unsupported_mode_code`	An unmapped integer mode cannot accidentally satisfy the heating-mode gate.
`auxiliary_stage_ends_one_step_before_persistence`	An auxiliary stage ending one evaluator step before 300 s never matures.
`mature_fault_recovers_when_auxiliary_clears`	A mature alarm clears immediately when the auxiliary source stops producing heat.
`two_short_auxiliary_episodes_reset`	Two short stages separated by a reset do not accumulate timer age.
`initialization_violation_serves_full_delay`	delayOnInit prevents an immediate alarm when evaluation starts inside the complete signature.
`defrost_interval_resets_candidate`	A defrost interval between two auxiliary stages resets persistence even though the other subconditions remain true.
`emergency_or_recovery_raw_case`	The raw graph alarms on sustained concurrent recovery/emergency heat; the host must exclude an authorized mode.

vectors.json

{
  "schema": "cxf-library/vectors/v1",
  "clock": {
    "step_s": 60,
    "horizon_s": 720
  },
  "scenarios": [
    {
      "name": "cooling_mode",
      "description": "Concurrent heat in the cooling code is diagnostically visible but outside the heating-mode candidate.",
      "inputs": {
        "aux_heat_status": true,
        "oat": 6.0,
        "mode_command": 2,
        "defrost_status": false,
        "comp_status": true
      },
      "expect": [
        {
          "output": "yHeatingMode",
          "from_s": 0,
          "to_s": 720,
          "equals": false
        },
        {
          "output": "yAboveLockout",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yConcurrentHeat",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yFault",
          "from_s": 0,
          "to_s": 720,
          "equals": false
        }
      ]
    },
    {
      "name": "heating_below_lockout",
      "description": "Auxiliary support below the configured lockout is permitted by this rule.",
      "inputs": {
        "aux_heat_status": true,
        "oat": 4.9,
        "mode_command": 1,
        "defrost_status": false,
        "comp_status": true
      },
      "expect": [
        {
          "output": "yHeatingMode",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yAboveLockout",
          "from_s": 0,
          "to_s": 720,
          "equals": false
        },
        {
          "output": "yConcurrentHeat",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yFault",
          "from_s": 0,
          "to_s": 720,
          "equals": false
        }
      ]
    },
    {
      "name": "heating_above_lockout_without_auxiliary",
      "description": "Compressor heating above lockout is healthy when the auxiliary source is inactive.",
      "inputs": {
        "aux_heat_status": false,
        "oat": 6.0,
        "mode_command": 1,
        "defrost_status": false,
        "comp_status": true
      },
      "expect": [
        {
          "output": "yHeatingMode",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yAboveLockout",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yConcurrentHeat",
          "from_s": 0,
          "to_s": 720,
          "equals": false
        },
        {
          "output": "yFault",
          "from_s": 0,
          "to_s": 720,
          "equals": false
        }
      ]
    },
    {
      "name": "auxiliary_above_lockout_compressor_off",
      "description": "Auxiliary heat without compressor proof may be emergency operation and is not this concurrent-energy signature.",
      "inputs": {
        "aux_heat_status": true,
        "oat": 6.0,
        "mode_command": 1,
        "defrost_status": false,
        "comp_status": false
      },
      "expect": [
        {
          "output": "yHeatingMode",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yAboveLockout",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yConcurrentHeat",
          "from_s": 0,
          "to_s": 720,
          "equals": false
        },
        {
          "output": "yFault",
          "from_s": 0,
          "to_s": 720,
          "equals": false
        }
      ]
    },
    {
      "name": "concurrent_heat_above_lockout_sustained",
      "description": "The complete avoidable-energy signature matures only after persistence.",
      "inputs": {
        "aux_heat_status": true,
        "oat": 6.0,
        "mode_command": 1,
        "defrost_status": false,
        "comp_status": true
      },
      "expect": [
        {
          "output": "yHeatingMode",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yAboveLockout",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yConcurrentHeat",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yFault",
          "from_s": 0,
          "to_s": 240,
          "equals": false
        },
        {
          "output": "yFault",
          "from_s": 360,
          "to_s": 720,
          "equals": true
        }
      ]
    },
    {
      "name": "concurrent_heat_during_defrost",
      "description": "Defrost explicitly removes the alarm candidate while leaving diagnostic subconditions visible.",
      "inputs": {
        "aux_heat_status": true,
        "oat": 6.0,
        "mode_command": 1,
        "defrost_status": true,
        "comp_status": true
      },
      "expect": [
        {
          "output": "yHeatingMode",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yAboveLockout",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yConcurrentHeat",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yFault",
          "from_s": 0,
          "to_s": 720,
          "equals": false
        }
      ]
    },
    {
      "name": "exact_oat_lockout_is_clear",
      "description": "The exact configured OAT threshold is clear under strict greater-than semantics.",
      "inputs": {
        "aux_heat_status": true,
        "oat": 5.0,
        "mode_command": 1,
        "defrost_status": false,
        "comp_status": true
      },
      "expect": [
        {
          "output": "yHeatingMode",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yAboveLockout",
          "from_s": 0,
          "to_s": 720,
          "equals": false
        },
        {
          "output": "yConcurrentHeat",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yFault",
          "from_s": 0,
          "to_s": 720,
          "equals": false
        }
      ]
    },
    {
      "name": "unsupported_mode_code",
      "description": "An unmapped integer mode cannot accidentally satisfy the heating-mode gate.",
      "inputs": {
        "aux_heat_status": true,
        "oat": 6.0,
        "mode_command": 0,
        "defrost_status": false,
        "comp_status": true
      },
      "expect": [
        {
          "output": "yHeatingMode",
          "from_s": 0,
          "to_s": 720,
          "equals": false
        },
        {
          "output": "yAboveLockout",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yConcurrentHeat",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yFault",
          "from_s": 0,
          "to_s": 720,
          "equals": false
        }
      ]
    },
    {
      "name": "auxiliary_stage_ends_one_step_before_persistence",
      "description": "An auxiliary stage ending one evaluator step before 300 s never matures.",
      "inputs": {
        "aux_heat_status": [
          {
            "t": 0,
            "value": true
          },
          {
            "t": 240,
            "value": false
          }
        ],
        "oat": 6.0,
        "mode_command": 1,
        "defrost_status": false,
        "comp_status": true
      },
      "expect": [
        {
          "output": "yFault",
          "from_s": 0,
          "to_s": 720,
          "equals": false
        },
        {
          "output": "yConcurrentHeat",
          "from_s": 0,
          "to_s": 180,
          "equals": true
        },
        {
          "output": "yConcurrentHeat",
          "from_s": 240,
          "to_s": 720,
          "equals": false
        }
      ]
    },
    {
      "name": "mature_fault_recovers_when_auxiliary_clears",
      "description": "A mature alarm clears immediately when the auxiliary source stops producing heat.",
      "inputs": {
        "aux_heat_status": [
          {
            "t": 0,
            "value": true
          },
          {
            "t": 420,
            "value": false
          }
        ],
        "oat": 6.0,
        "mode_command": 1,
        "defrost_status": false,
        "comp_status": true
      },
      "expect": [
        {
          "output": "yFault",
          "from_s": 0,
          "to_s": 240,
          "equals": false
        },
        {
          "output": "yFault",
          "from_s": 360,
          "to_s": 360,
          "equals": true
        },
        {
          "output": "yFault",
          "from_s": 420,
          "to_s": 720,
          "equals": false
        },
        {
          "output": "yConcurrentHeat",
          "from_s": 0,
          "to_s": 360,
          "equals": true
        },
        {
          "output": "yConcurrentHeat",
          "from_s": 420,
          "to_s": 720,
          "equals": false
        }
      ]
    },
    {
      "name": "two_short_auxiliary_episodes_reset",
      "description": "Two short stages separated by a reset do not accumulate timer age.",
      "inputs": {
        "aux_heat_status": [
          {
            "t": 0,
            "value": true
          },
          {
            "t": 180,
            "value": false
          },
          {
            "t": 300,
            "value": true
          },
          {
            "t": 480,
            "value": false
          }
        ],
        "oat": 6.0,
        "mode_command": 1,
        "defrost_status": false,
        "comp_status": true
      },
      "expect": [
        {
          "output": "yFault",
          "from_s": 0,
          "to_s": 720,
          "equals": false
        }
      ]
    },
    {
      "name": "initialization_violation_serves_full_delay",
      "description": "delayOnInit prevents an immediate alarm when evaluation starts inside the complete signature.",
      "inputs": {
        "aux_heat_status": true,
        "oat": 6.0,
        "mode_command": 1,
        "defrost_status": false,
        "comp_status": true
      },
      "expect": [
        {
          "output": "yFault",
          "from_s": 0,
          "to_s": 240,
          "equals": false
        },
        {
          "output": "yFault",
          "from_s": 360,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yHeatingMode",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yAboveLockout",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yConcurrentHeat",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        }
      ]
    },
    {
      "name": "defrost_interval_resets_candidate",
      "description": "A defrost interval between two auxiliary stages resets persistence even though the other subconditions remain true.",
      "inputs": {
        "aux_heat_status": true,
        "oat": 6.0,
        "mode_command": 1,
        "defrost_status": [
          {
            "t": 0,
            "value": false
          },
          {
            "t": 180,
            "value": true
          },
          {
            "t": 300,
            "value": false
          },
          {
            "t": 480,
            "value": true
          }
        ],
        "comp_status": true
      },
      "expect": [
        {
          "output": "yFault",
          "from_s": 0,
          "to_s": 720,
          "equals": false
        }
      ]
    },
    {
      "name": "emergency_or_recovery_raw_case",
      "description": "The raw graph alarms on sustained concurrent recovery/emergency heat; the host must exclude an authorized mode.",
      "inputs": {
        "aux_heat_status": true,
        "oat": 6.0,
        "mode_command": 1,
        "defrost_status": false,
        "comp_status": true
      },
      "expect": [
        {
          "output": "yFault",
          "from_s": 0,
          "to_s": 240,
          "equals": false
        },
        {
          "output": "yFault",
          "from_s": 360,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yHeatingMode",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yAboveLockout",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        },
        {
          "output": "yConcurrentHeat",
          "from_s": 0,
          "to_s": 720,
          "equals": true
        }
      ]
    }
  ]
}

open-control-library — CDL Fault Rule Library

HP-0008 — Auxiliary heat active above lockout with compressor running

Description

Detection Logic

Possible Diagnoses

Energy Impact

Emissions Impact

Deviations

Test Vectors

Keyboard shortcuts

open-control-library — CDL Fault Rule Library