BOVA 2.0

Outdoor T4 outside the allowed window (cool: T4 ≥125°F or <15°F; heat: T4 ≥86°F or <−4°F on IDS 2.0), or the reversing-valve call is wrong so the outdoor thinks it is in the wrong mode.

1. 1 Confirm O/B is energized the way THIS outdoor expects

   Most US splits energize O in cool. Some Rheem/Ruud energize B in heat. Read the Bosch BOVA 2.0 diagram, not a generic heat-pump card. Idle ≥5 min, compare T4 on the board to real outdoor temp (10K sensor, ~10 kΩ at 77°F).

   Expect: Correct 24 V at the solenoid for the mode that is failing.

2. 2 Listen for the valve, then measure

   A healthy valve slams. 24 V at the solenoid on the shift call? Voltage + no slam → valve mechanically stuck. No voltage → stat / defrost board / IFC. Heat call must energize B per the Bosch diagram. Y-only in heat, or B stuck on in cool, produces ATL.

   Expect: Solenoid voltage present. Pressures swap after the slam.

3. 3 Stuck valve vs a defrost board that never leaves cool

   A defrost board stuck in defrost looks like ‘no heat’ with the OD fan off. If the valve is energized and pressures never swap, recover and replace the valve — do not beat on it as a repair. 18–28 VAC B–C at the outdoor during a heat call.

   Expect: Mode change on the gauges. OD fan on in heat except during a real defrost.

T3 reads implausible vs T4 (T3 < T4 − 3°F for 10 min).

1. 1 Which sensor is this code?

   On Bosch BOVA 2.0 C3 / C4 is a specific thermistor — indoor return/pipe, outdoor coil, discharge, or ambient. Unplug that sensor and ohm it vs the OEM temperature/resistance chart. T3 on the outdoor coil U-bend per the diagram, not hanging in air.

   Expect: Ohms move with temperature. Not open, not shorted.

2. 2 Seating and the harness

   A sensor that ohms good on the bench and fails in the unit is seating or a rubbed harness. Reseat in the well / on the coil, check the plug at the board. T3/T4 10K ohms. 18 SEER has one T3; some 15/20 SEER have T3 and T3L.

   Expect: Sensor fully in the well. Harness not pinched.

3. 3 Board input last

   Known-good sensor + known-good harness and the code stays = Bosch BOVA 2.0 control input. Do not replace every sensor on the unit.

   Expect: Code clears with a known-good sensor at the board.

T3, T3L, T4, T5, or TF out of range.

1. 1 Which sensor is this code?

   On Bosch BOVA 2.0 E4 is a specific thermistor — indoor return/pipe, outdoor coil, discharge, or ambient. Unplug that sensor and ohm it vs the OEM temperature/resistance chart. Identify which sensor the display names.

   Expect: Ohms move with temperature. Not open, not shorted.

2. 2 Seating and the harness

   A sensor that ohms good on the bench and fails in the unit is seating or a rubbed harness. Reseat in the well / on the coil, check the plug at the board. T3/T4/T3L: 10K. T5/TF: 5K class — use the IDS ohm chart. Open/shorted harness vs failed bulb.

   Expect: Sensor fully in the well. Harness not pinched.

3. 3 Board input last

   Known-good sensor + known-good harness and the code stays = Bosch BOVA 2.0 control input. Do not replace every sensor on the unit.

   Expect: Code clears with a known-good sensor at the board.

Line voltage out of band (IDS: operate ~180–270 V; typical run ≥210 V).

1. 1 Measure at the IFC under load

   On Bosch BOVA 2.0 line-voltage codes are incoming power. Measure L1/L2 (or L1/N) at the board while it is trying to run, not just at the disconnect. L1–L2 at the outdoor. A just-pulled disconnect can E5 on the inrush — wait and recheck.

   Expect: Voltage in the rating-plate window under load.

2. 2 Drop, breaker, and the whip

   Large drop from the disconnect to the IFC is a loose lug or damaged whip. Breaker that will not hold under inducer/blower start is the circuit, not the board. This is line voltage, not a 24 V stat brownout. Still verify 18–28 VAC Y–C at the AHU so you do not chase the drive for a dead transformer.

   Expect: Minimal drop. Tight lugs. Correct breaker size.

3. 3 Transformer 24 V last

   If line is good and 24 V is low, load the transformer (stat + valve + accessories). A collapsing 24 V looks like a comm or fuse call.

   Expect: 24 V holds under load. Line stays in window.

Outdoor fan failed or the board is not driving it.

1. 1 Let it cool, then read the drive LED

   On Bosch BOVA 2.0 overcurrent / overheat is often a dirty coil, a failed OD fan, or a locked compressor — not a dead inverter. Clear airflow, confirm the OD fan, and read the drive LED before you order a control. Blade free? Ice/wind lock?

   Expect: OD fan running. Coil clean. Drive LED decoded from THIS outdoor’s card.

2. 2 Voltage and compressor windings

   Incoming voltage in range (this plate’s line-voltage code). Compressor windings even, no ground. A shorted compressor will kill a new drive. Motor vs board: resistance and drive voltage per the 5-wire or 3-wire diagram on THIS BOVA.

   Expect: Balanced windings. No winding to ground. Line voltage stable under load.

3. 3 Charge and the drive last

   A starved or flooded compressor will overcurrent. Confirm SH/SC and charge weight. Only then condemn the inverter. A dead outdoor fan becomes P1/P0 next.

   Expect: Charge on the nameplate. Drive code gone after a cool-down and a clean coil.

T5 not tracking (T5 < T3 − 5°F in cool, or similar band in heat, for 10 min) — plug not on the discharge or a real high-discharge event.

1. 1 Which sensor is this code?

   On Bosch BOVA 2.0 E7 is a specific thermistor — indoor return/pipe, outdoor coil, discharge, or ambient. Unplug that sensor and ohm it vs the OEM temperature/resistance chart. T5 fully on the discharge tube. 5K sensor.

   Expect: Ohms move with temperature. Not open, not shorted.

2. 2 Seating and the harness

   A sensor that ohms good on the bench and fails in the unit is seating or a rubbed harness. Reseat in the well / on the coil, check the plug at the board. If T5 is seated and hot, that is charge / restriction / P4 territory — do not just reseat forever.

   Expect: Sensor fully in the well. Harness not pinched.

3. 3 Board input last

   Known-good sensor + known-good harness and the code stays = Bosch BOVA 2.0 control input. Do not replace every sensor on the unit.

   Expect: Code clears with a known-good sensor at the board.

Outdoor control EEPROM / memory chip.

1. 1 Write the live code and watch one cycle

   On Bosch BOVA 2.0 read BOVA outdoor inverter PCB + BVA indoor board before you pull power. Write E9 exactly. Watch one full sequence and note which step dies. L1–L2 in range. If E9 remains, the outdoor board — not a Daikin indoor IFC.

   Expect: Stat call: 24 V at the AHU (Y cool, B/O reversing, G fan, W strips). The AHU then talks to the outdoor on the comm cable. No Y at the outdoor like a contactor unit.

2. 2 Prove the circuit this code names

   Do not ‘reprogram’ this like ComfortBridge shared data.

   Expect: A measured open, short, or out-of-range reading — not a guess.

3. 3 Confirm with a number, then the next part

   If the named part measures good, the IFC input/output or a related code on this same plate is next. Do not apply a sister-SKU chart.

   Expect: Stat vs comm: 24 V at the AHU. Communicating pair indoor–outdoor only. Never 24 VAC on the comm pins.

Communication fault in the main control / EEPROM seating. Field: indoor–outdoor handshake and the outdoor board itself.

1. 1 Data pair, not 24 V

   On Bosch BOVA 2.0 indoor/outdoor comm is a data pair (AB, S1/S2, U, ComfortBridge, ComfortLink — whatever THIS plate uses). It is not a 24 V Y. Check polarity, continuity, and that nobody landed it on R/C. Dedicated comm cable BVA↔BOVA landed on the comm terminals — not the 24 V stat cable.

   Expect: Pair continuous, not shorted to chassis, polarity per the diagram.

2. 2 Power both ends, then the outdoor status

   Indoor transformer and outdoor control both alive. Read the outdoor LED / 7-seg. Water in the outdoor control is the usual dead-end after a storm. EEPROM chip fully seated / not backwards on boards that have a plug-in chip.

   Expect: Both controls powered. Outdoor showing a comm or address state, not a blank board.

3. 3 Address / bias, then the control

   Communicating plates need a matching indoor address and sometimes a terminating bias. Swap is last: known-good pair + power both ends + correct address. L1–L2 in range. H0 that survives a good comm cable and good power is the outdoor board.

   Expect: Indoor sees the outdoor. No comm code after a power cycle.

Suction PT failed or disagrees with gauges.

1. 1 Heat rejection first

   On Bosch BOVA 2.0 high pressure is outdoor airflow until proven otherwise. Fan running the right direction, coil clean, fins not folded, no recirc over a fence or through a garage. PT wiring. Idle PT vs manifold (±50 psi class on IDS).

   Expect: OD fan on, coil clean, discharge air leaving the top/side freely.

2. 2 Head, subcooling, and liquid line

   Liquid pressure and liquid-line temperature → SC. High head + high SC = overcharge or non-condensables. High head + low SC = restriction or a dying compressor. Do not add gas because suction is low. Supply ~5 VDC on the transducer reference. Bad PT vs bad board.

   Expect: SC vs the metering device on this plate (TXV ≠ piston).

3. 3 Restriction vs the switch

   Drier, liquid-line kink, TXV inlet screen, or a non-feed indoor coil will stack head. Ohm / jumper-test the HPS only as a momentary prove, then restore it. A switch that opens on a known-good charge and clean coil is the switch.

   Expect: HPS closed at a normal liquid pressure for this refrigerant and OD ambient.

T3 outdoor-coil overtemp.

1. 1 Let it cool, then read the drive LED

   On Bosch BOVA 2.0 overcurrent / overheat is often a dirty coil, a failed OD fan, or a locked compressor — not a dead inverter. Clear airflow, confirm the OD fan, and read the drive LED before you order a control. Outdoor coil and inverter heat sink clean. Fan running (see E6).

   Expect: OD fan running. Coil clean. Drive LED decoded from THIS outdoor’s card.

2. 2 Voltage and compressor windings

   Incoming voltage in range (this plate’s line-voltage code). Compressor windings even, no ground. A shorted compressor will kill a new drive. T3/TF readings in the parameter list.

   Expect: Balanced windings. No winding to ground. Line voltage stable under load.

3. 3 Charge and the drive last

   A starved or flooded compressor will overcurrent. Confirm SH/SC and charge weight. Only then condemn the inverter.

   Expect: Charge on the nameplate. Drive code gone after a cool-down and a clean coil.

HPS opened (airflow, overcharge, restriction, or failed switch).

1. 1 Heat rejection first

   On Bosch BOVA 2.0 high pressure is outdoor airflow until proven otherwise. Fan running the right direction, coil clean, fins not folded, no recirc over a fence or through a garage. Outdoor fan and coil. Indoor filter/coil.

   Expect: OD fan on, coil clean, discharge air leaving the top/side freely.

2. 2 Head, subcooling, and liquid line

   Liquid pressure and liquid-line temperature → SC. High head + high SC = overcharge or non-condensables. High head + low SC = restriction or a dying compressor. Do not add gas because suction is low. HPS (2 yellow leads on IDS) ohms closed when idle and cool.

   Expect: SC vs the metering device on this plate (TXV ≠ piston).

3. 3 Restriction vs the switch

   Drier, liquid-line kink, TXV inlet screen, or a non-feed indoor coil will stack head. Ohm / jumper-test the HPS only as a momentary prove, then restore it. A switch that opens on a known-good charge and clean coil is the switch. Charge is weigh-in / Bosch subcooling chart — not piston SH.

   Expect: HPS closed at a normal liquid pressure for this refrigerant and OD ambient.

Low-pressure protection in cool, or high discharge superheat protection in heat (IDS: <44 psi for 5 min cool; high discharge SH band in heat).

1. 1 Confirm this is not a fault

   On the Bosch BOVA 2.0 this readout (P2) is run status, not a lockout. Write what the display actually shows and whether W/Y/G is present at the IFC.

   Expect: Idle / Ht / CF / stage+CFM words change when you apply and remove the call.

   If fail: If the word never changes on a real call, the call is not reaching this IFC.

   If pass: The board is alive. Diagnose the comfort complaint, not this code.

2. 2 Prove the call at the board

   Measure R to W / Y / G at the Bosch BOVA 2.0 IFC, not at the thermostat. Communicating plates need the data pair and a live indoor address — 24 V on W is not the test.

   Expect: Service valves open. Indoor blower on a cool call; outdoor fan on a heat call.

   If fail: Fix the stat, harness, or data pair before you change parts.

3. 3 Watch one full sequence

   Leave power on. Watch BOVA outdoor inverter PCB + BVA indoor board through one cycle and write the first real fault that replaces this status word.

   Expect: Stat call: 24 V at the AHU (Y cool, B/O reversing, G fan, W strips). The AHU then talks to the outdoor on the comm cable. No Y at the outdoor like a contactor unit.

Inverter current out of band (tonnage-specific trip on the IDS card).

1. 1 Let it cool, then read the drive LED

   On Bosch BOVA 2.0 overcurrent / overheat is often a dirty coil, a failed OD fan, or a locked compressor — not a dead inverter. Clear airflow, confirm the OD fan, and read the drive LED before you order a control. Valves open, coils clean, outdoor fan running, outdoor <125°F.

   Expect: OD fan running. Coil clean. Drive LED decoded from THIS outdoor’s card.

2. 2 Voltage and compressor windings

   Incoming voltage in range (this plate’s line-voltage code). Compressor windings even, no ground. A shorted compressor will kill a new drive. Overcharge and a locked compressor both P3 — weigh-in and windings before you order a drive.

   Expect: Balanced windings. No winding to ground. Line voltage stable under load.

3. 3 Charge and the drive last

   A starved or flooded compressor will overcurrent. Confirm SH/SC and charge weight. Only then condemn the inverter.

   Expect: Charge on the nameplate. Drive code gone after a cool-down and a clean coil.

T5 overtemp (IDS trips in steps up to a 230°F-class shutdown).

1. 1 Let it cool, then read the drive LED

   On Bosch BOVA 2.0 overcurrent / overheat is often a dirty coil, a failed OD fan, or a locked compressor — not a dead inverter. Clear airflow, confirm the OD fan, and read the drive LED before you order a control. Weigh-in / Bosch chart (undercharge is the usual P4).

   Expect: OD fan running. Coil clean. Drive LED decoded from THIS outdoor’s card.

2. 2 Voltage and compressor windings

   Incoming voltage in range (this plate’s line-voltage code). Compressor windings even, no ground. A shorted compressor will kill a new drive. Valves open, indoor blower, outdoor coil, T5 seated.

   Expect: Balanced windings. No winding to ground. Line voltage stable under load.

3. 3 Charge and the drive last

   A starved or flooded compressor will overcurrent. Confirm SH/SC and charge weight. Only then condemn the inverter.

   Expect: Charge on the nameplate. Drive code gone after a cool-down and a clean coil.

Strip kit opened a limit / sequencer. This is AHU airflow or a bad element, not a BOVA P-code.

1. 1 Is aux actually being requested?

   On Bosch BOVA 2.0 confirm W / E / aux at the indoor control. A heat-pump call with a communicating board that thinks it needs strips is a config / outdoor issue first. Filter, blower, heat-kit size vs the BVA nameplate.

   Expect: Aux request present only when it should be.

2. 2 Sequencer and each element

   24 VAC at each sequencer coil, then line through each element. Open element vs a dead sequencer are different parts. Limit on a strip is airflow or a failed limit. W at the AHU calling strips because HP failed (RV, sensors, ATL) — fix the HP before you upsize strips.

   Expect: Each element comes on in sequence. Limits closed.

3. 3 Airflow across the strips

   Strips without enough CFM open limits immediately. Confirm blower heat/aux tap or communicating electric-heat CFM before you change sequencers. No Carrier 33 and no Daikin E3 on this limit string.

   Expect: Blower on before or with the first element. Limits stay closed.