Heat Pump Error Codes

Common UK Heat Pump Error Codes Explained: Causes & Fixes

Heat pumps are becoming increasingly popular across the UK as an energy-efficient way to heat homes. However, like any heating system, they can occasionally display error codes that indicate a problem.

Understanding what these codes mean can help you identify simple fixes—or know when it’s time to call in a professional.

First Step: Try a Reset

Before investigating any error code:

👉 Turn the system off at the isolator for 5–10 minutes, then switch it back on.

This can often clear temporary faults and restore normal operation.

Most Common Heat Pump Error Codes

Flow Errors (F20 / Hp / Lp / Various Codes)

This is one of the most common heat pump issues and usually relates to poor water circulation.

Common causes:

• Blocked or dirty filters

• Airlocks in the system

• Circulation pump failure

What to do:

• Check and clean filters/strainers

• Ensure valves are open

• Bleed air from the system if needed

Low Pressure Errors (E911 / tP / F22)

This indicates that the system pressure has dropped too low for safe operation.

What to do:👉 Re-pressurise the system to between 1.5 and 2 bar

If pressure keeps dropping, there may be a leak that needs professional attention.

Outdoor Sensor Fault (E3 / E04 / F11)

The system cannot read the outdoor temperature, which affects efficiency and performance.

Possible causes:

• Faulty sensor

• Damaged wiring

• Loose connections

👉 This typically requires inspection and repair by an engineer.

High / Low Pressure Circuit Fault (E1 / E02)

This relates to the refrigerant circuit, which is critical to how your heat pump operates.

Possible issues:

• Refrigerant leaks

• Blockages

• Ice build-up

• Compressor problems

⚠️ These faults should always be handled by a qualified professional.

Communication Fault (E7 / E8)

This means the indoor unit and outdoor unit are not communicating properly.

Common causes:

• Wiring faults

• Power supply issues

• PCB/control board problems

Overcurrent / Defrost Failure (F1 / F2 / E6 / U6)

These errors are often linked to electrical or defrost cycle issues.

What can happen:

• Ice builds up on the outdoor unit

• System struggles to maintain efficiency

• Electrical surges trigger shutdown

👉 If this persists, it will need professional diagnosis.

Simple Checks You Can Do

Before calling an engineer, try the following:

• ✅ Check system pressure (should be 1.5–2 bar)

• ✅ Clean filters and strainers

• ✅ Reset the system

• ✅ Check for obvious leaks or ice build-up

When to Call a Professional

You should contact a qualified engineer if:

• Error codes keep returning

• You suspect a refrigerant issue (E1, E02)

• Electrical faults appear (U6, E6)

• The system loses pressure repeatedly

• You’re unsure how to proceed

Heat pumps are complex systems, and attempting advanced repairs without the right qualifications can cause further damage.

Heat Pump Repairs in Bexhill, Hastings & Eastbourne

At Forward Thermal and Flow, we provide expert fault finding, servicing, and repairs for heat pump systems across:

• Bexhill-on-Sea

• Hastings

• Battle

• Eastbourne

• Surrounding areas

Whether it’s a flow issue, pressure fault, or system error, our experienced team is here to help keep your heating running efficiently.

Need Help With Your Heat Pump?

If your heat pump is showing an error code or not performing as it should:

👉 Contact Forward Thermal and Flow today for reliable, professional support.