Bosch IDS Heat Pump Error Codes: E5, P1, H5 and AtL

By Ray Bennett · Updated 2 October 2026 · 6 min read · Checked against the maker’s manual

Bosch IDS Heat Pump Error Codes: E5, P1, H5 and AtL

Short answer

On a Bosch IDS 2.0 heat pump, AtL, dF and a letter followed by two numbers are not faults: the unit is outside its temperature range, defrosting, or running in a limited way. E5 is the power supply, E6 and P8 the outdoor fan, H5 a lockout that needs the power switched off and on, and the P codes are pressure and temperature protections for a technician.

The Bosch IDS 2.0 is an inverter heat pump. Its outdoor unit, the BOVA, speeds its compressor up and down instead of just switching on and off. It shows codes on a small display on the control board inside the outdoor unit, and some of what appears there is not a fault at all.

Everything on this page comes from Bosch’s own installation, operation and maintenance manual for the IDS 2.0 BOVA. Bosch says any maintenance and repair of the outdoor unit is for qualified service people. So most of this page is about knowing what a code means, and which few things are yours to check.

Before you start

What to carry: a torch, and your phone to photograph the code. Five minutes.

Gas or electric? Electric. The outdoor unit runs on a 208 or 230 volt supply.

Where the code shows. On the display of the main control board in the outdoor unit. The board sits behind a service panel, so leave opening it to the technician.

What normal looks like. Bosch says that with no fault, the display shows the outdoor temperature while the unit waits, and the compressor speed while it runs.

What Bosch says to leave alone. 380 volts inside. Bosch warns that parts in the outdoor unit can hold a charge of 380 volts DC after the power is off. Its technicians wait three minutes and measure before touching anything.

Power off for any check. Bosch says to turn the heat pump off and disconnect the power before cleaning or maintenance.

After a long cold shutdown. Bosch recommends powering the unit with the thermostat off for at least 12 hours before the compressor runs. That lets the crankcase heater warm the compressor.

Readings that are not faults

Four things Bosch's display shows that need no repair: AtL, dF, a status letter with the compressor speed, and E4 in deep cold.

Check 1Free, two minutes

Read it before you worry

AtL: outside its temperature range. Bosch’s range is 15 to 125°F for cooling and -4 to 86°F for heating. Outside it, Bosch’s chart says no service is required: wait for the temperature to come back.

Below -4°F. Bosch says the heat pump then sends the call to the indoor unit’s electric heat, if it has any.

dF: defrost. Bosch says the display shows dF alone while the unit defrosts its outdoor coil: why a heat pump ices up in winter.

A letter, then two numbers. Bosch says the unit keeps running in a limited way, and the two numbers are the compressor speed. L, D, F and C mean it is holding back for coil temperature, discharge temperature, module temperature or current. U is low voltage, P is the compressor ratio and A is oil return.

E4 in deep cold. Bosch’s E4 chart says no service is required when it is below -4°F outside.

A minute of cooling. Bosch says that on first time operation, a heat call runs about a minute in cooling to build pressure for the reversing valve.

Codes with an owner check

Check 2Free, fifteen minutes

Work the owner checks

E5: high or low voltage. Bosch’s chart checks the supply for 270 volts or more, or 172 volts or less. The fix is the supply, and Bosch names the utility company.

E6 and P8: the outdoor fan. Bosch’s charts ask whether the weather is stopping the fan. If so, power the unit off until the severe weather passes. Bosch calls P8 its hurricane or typhoon protection.

E6 and a blocked fan. Bosch’s chart also asks whether something is blocking the fan or the blade is damaged: power off, then clear it.

H5: a lockout. Bosch says low pressure protection tripped five times in 100 minutes, and H5 needs a hard restart, meaning the power off and on. If it comes back, the low pressure needs a technician.

Air in and out. Bosch’s check at the start of each season: power off, look for damaged wires and leaks, and make sure nothing blocks the air inlets and outlets. It asks for at least 12 inches to shrubs.

Snow and ice

Bosch's cold climate advice: raise the unit 3 to 12 inches, keep the drain holes open, and keep drifts and roof drips off it.

Check 3

Keep it clear in winter

Raised. Bosch says to raise the unit 3 to 12 inches above the pad, so the water from defrost drains away before it can refreeze.

Drain holes. Bosch says the drain holes in the base pan must not be blocked.

Drifts and drips. Bosch says to avoid spots prone to snow drifts, or to fit a snow barrier, and to keep water, snow or ice from a roof or overhang from falling on the unit.

Every code in Bosch’s table

Code	What Bosch calls it
C3	Outdoor coil sensor not seated right, in cooling
E4	Temperature sensor fault
E5	High or low voltage protection
E6	Outdoor fan motor fault
E7	Discharge sensor not seated right
E9	EEPROM fault
H0	Communication fault in the main control chip
H5	Low pressure five times in 100 minutes, lockout
H8	Pressure transducer fault
P0	Control board module too hot
P1, F1	High pressure switch protection
P2	Low pressure protection
P3	Compressor over current
P4	Compressor discharge too hot
P5	Outdoor coil too hot in cooling
P8	Fan protection in hurricane or typhoon winds
PH	Low discharge superheat
L0 to L9	Inverter module protection
AtL	Outside temperature beyond its range

When it needs a technician

Check 4A service call

Know when to stop

P1, P3, P4, P5 and PH. Bosch’s charts check the service valves, the refrigerant charge, the airflow and whether it is over 120°F outside. Refrigerant work needs a licensed technician: the signs of a refrigerant leak.

Sensor and board codes. C3, E7, E9, H0 and H8, and E4 in normal weather, point to wiring, a sensor or the control board.

L0 to L9. Bosch’s chart starts with whether the power supply is stable, then moves to the refrigerant circuit and the compressor.

Heating stopped altogether. The wider checks for a heat pump that blows cold are here: why a heat pump is not heating.

Questions people ask

What does AtL mean on a Bosch heat pump?

Ambient temperature limited: it is too hot or too cold outside for the heat pump to run. Bosch says no service is required, so wait for the temperature to come back into range.

What does dF mean?

Defrost. The unit is melting ice off its outdoor coil, and the display shows dF alone until it finishes.

What does E5 mean on a Bosch IDS?

High or low voltage. Bosch’s chart checks for 270 volts or more, or 172 volts or less, and the fix is the power supply.

What does H5 mean?

A lockout after five low pressure trips in 100 minutes. It needs the power switched off and on, and a technician if it returns.

Why does the display show a letter and a number?

The unit is running in a limited way, for example holding back for coil temperature or low voltage. The number is the compressor speed. It is not a fault.

Can I clean the outdoor unit myself?

Bosch says maintenance and cleaning of the outdoor unit are for qualified service people. What you can do is keep snow, leaves and plants clear of it.

Sources: Bosch IDS 2.0 BOVA installation, operation and maintenance manual (04.2021), from bosch-homecomfort.com