Error codes are designed to help users identify and troubleshoot any issues that may arise with their refrigeration unit.
Here is a comprehensive list of the most commonly encountered error codes and their corresponding descriptions.
| Error code/ indication | Probable Cause |
| dEF | Defrost in progress |
| oFF | Controller in stand-by |
| cL | Condenser clean warning |
| do | Door open alarm |
| hc | Condenser high temperature alarm |
| t1 | Instant probe 1 temperature |
| t2 | Instant probe 2 temperature |
| t3 | Instant probe 3 temperature |
| th1 | Maximum probe 1 temperature recorded |
| hP | Condenser high pressure alarm |
| h1 | Room high temperature alarm |
| Lo | Room low temperature alarm |
| E1 | Probe T1 failure |
| E2 | Probe T2 failure |
| tLo | Minimum probe 1 temperature recorded |
| cnd | Compressor working weeks |
| Loc | Keypad state lock |
What to Do When You See a Foster Error Code
Before calling an engineer, there are a few steps you can safely try yourself:
- Note the code down - Write down the exact error code displayed. If the code is flashing or alternating, note the full sequence.
- Power cycle the unit - Switch the refrigeration unit off at the isolator, wait 60 seconds, then switch it back on. This can clear temporary sensor glitches.
- Check the basics - Make sure the door seals properly, the condenser coils are clear of dust, and airflow around the unit is not blocked.
- Check the temperature - Verify the setpoint has not been accidentally changed.
If the error code returns after a power cycle, or if you see codes related to high pressure, compressor failure, or refrigerant issues, do not attempt a DIY fix. These require a qualified engineer with the right tools and certifications.
When to Call a Professional
Some faults need immediate professional attention to avoid further damage or safety risks:
- Refrigerant-related codes - Any error pointing to pressure problems or gas leaks must be handled by an F-Gas certified engineer. Under UK law, only qualified personnel can handle refrigerants.
- Electrical faults - PCB errors, overcurrent warnings, or voltage issues can be dangerous. Switch the unit off at the isolator and call a qualified technician.
- Repeated alarms - If the same error code keeps coming back after a reset, there is an underlying issue that needs proper diagnosis.
- Food safety concerns - If your unit stores perishable goods and the temperature has risen above safe levels, you may need to assess stock safety. The Food Standards Agency recommends keeping chilled food below 8°C and frozen food at -18°C or below.
UK Regulations for Commercial Refrigeration Maintenance
If you operate commercial refrigeration in the UK, you should be aware of these key regulations:
- F-Gas Regulation - Equipment containing fluorinated greenhouse gases must be regularly inspected for leaks. Systems with 5 tonnes CO2 equivalent or more require leak checks at set intervals. See the UK Government F-Gas guidance for full details.
- Food Hygiene Regulations 2006 - Businesses storing food must maintain correct temperatures and keep records. The Food Standards Agency temperature control guidance covers the legal requirements.
- HACCP Compliance - Your Hazard Analysis and Critical Control Points plan should include refrigeration monitoring. Temperature logs and alarm response procedures are key parts of any HACCP system.
Regular maintenance is not just good practice, it is a legal requirement for many businesses. At Be Cool Refrigeration, all our engineers are F-Gas certified and can help you stay compliant.
Written by
Ali Elm
Ali is the Head of Operations at Be Cool Refrigeration with over a decade of hands-on experience in HVAC and commercial refrigeration. He oversees every installation, repair, and maintenance project, making sure the work meets the highest standards. Ali holds full F-Gas certification and has worked across residential, commercial, and industrial refrigeration systems throughout London and the South East. When he is not on site, he writes these guides to help business owners and homeowners understand their cooling systems better.