A CTC heat pump error code is an alarm, written as an E followed by numbers such as E135 or E035, that tells you which part of the system has stopped working as it should. On most recent CTC air source models you will not see it on the outdoor unit. It appears on the controller the heat pump is paired with, such as a CTC EcoZenith, EcoLogic or EcoVent display, while older EcoAir 105 to 111 units show shorter codes like E01 on their own built-in screen.
This guide explains the CTC codes homeowners see most, what usually causes them and what you can safely check. For codes from other makes, our heat pump error codes hub covers the wider picture.
One safety point before you start: never open the casing of the indoor or outdoor unit, because both contain mains voltage and pressurised refrigerant. If a code keeps coming back, or you are not sure what it means, book a heat pump repair and one of our F-Gas certified engineers will diagnose it properly.
Is it safe to fix a CTC heat pump fault yourself?
Only up to a point: you can safely make basic outside checks, but anything inside the units is a job for a qualified engineer. That means looking at the pressure gauge, checking valves are open, clearing leaves or loose snow from around the outdoor unit and checking your consumer unit for a tripped breaker.
Do not remove panels or touch wiring, fuses or circuit boards. Several CTC alarms point to the refrigerant circuit, and in the UK only F-Gas certified engineers are legally allowed to work on it.
There is also your warranty to think about. Unqualified work on the unit can affect manufacturer or installer cover, so if in doubt, stop and call someone.
Please read first: this guide is here to help you understand what your CTC heat pump is telling you. Every effort has been made to keep the information accurate, but manufacturers update their manuals and codes can differ between models and software versions, so always check the official CTC manual for changes before acting on anything here. Do not attempt anything that could be dangerous, and avoid any work that could void your warranty. If in doubt, call a qualified heat pump engineer.
If your CTC heat pump is not showing a code, or you want to rule out the basics first, our guide to heat pump not working walks through the general checks and matches common faults to error codes across every major brand.
Which CTC error codes can you check yourself?
A handful of CTC codes have a realistic first check you can do from outside the unit. The rest need an engineer, so if your code is not in this table, skip straight to booking one.
| Code | What it means | Safe homeowner check | Stop and call an engineer if |
|---|---|---|---|
| E135 | Risk of freezing during defrost | Check the pressure gauge is in the range your installer set, radiator and isolation valves are open, and the outdoor unit is not blocked by snow or leaves | It returns after a reset, or the controller shows it as a critical alarm |
| E211 | Water flow too low during defrost (EcoAir 600M with flow sensor, 700M) | Same as E135: pressure, open valves, clear airflow | It comes back at all, as low flow in defrost risks freezing the heat exchanger |
| E163 | Defrost took too long to finish | Look at the outdoor coil from outside. Brush away loose snow or leaves by hand, but never chip or scrape ice | The coil stays iced over or the code returns |
| E216, E217 | Flow temperature gap too wide, or charge pump working too hard | Check system pressure and that radiator valves are open | It recurs, as the dirt filter or pump speed needs checking |
| E01, E02 (older EcoAir 105 to 111) | High or low pressure switch tripped | Check heating valves are open and the fan is not blocked by ice or debris | It trips again after the reset described below |
| E052, E053, E054 | One of the three supply phases is missing | Check your consumer unit for a tripped breaker and whether there is a local power problem | Power is fine but the code stays |
| E026 | The heat pump itself is in alarm | Read the controller for the heat pump's own alarm and write it down | Always: the underlying alarm needs diagnosing |
| E074, E075 | Room sensor 1 or 2 fault | Check the wall-mounted room sensor is still in place and not damaged | It does not clear once the sensor is back in place |
If you want to know what normal ice looks like before you worry, our guide to a heat pump frozen outside unit explains the difference.
What are the most common CTC heat pump error codes?
The most common CTC codes relate to freezing risk in defrost, poor water flow and high pressure. Where we add causes the CTC manuals do not mention, we label them as general engineering knowledge.
E135 and E211: risk of freezing
E135 means the water leaving the heat pump fell below 15 °C during defrost, or the in and out temperatures were more than 15 °C apart for 20 seconds. E211 means flow stayed under 10 litres a minute during defrost (15 on the 622 model). CTC points to low circuit temperature, low flow, or faulty HP in and HP out sensors.
From general engineering knowledge, low flow often comes from sludge in radiators, a blocked strainer, an air lock or a pump set too low. A small system with no buffer tank may also hold too little water to defrost safely. Make the pressure and valve checks above, then call us; our guide to the heat pump defrost cycle explains why defrost needs warm water to work.
E163: defrost not completed
E163 shows when defrost runs past its maximum time without clearing the evaporator. CTC says to check the evaporator is free of ice. General engineering knowledge adds that a blocked or frozen condensate route can stop the coil clearing, so if ice keeps building, an engineer should check the drain and defrost control.
E216 and E217: flow temperature difference
E216 means the inlet and outlet temperatures were more than 12 °C apart for 15 minutes while heating (EcoAir 500, 600M and 700M). E217 means the charge pump ran above 70% for 15 minutes on an EcoAir 400. CTC's advice is to check the dirt filter, pipework and pump speed, and after four alarms these become E218 to E221 and the heat pump locks.
If radiators are also cooler than usual, see our article on a heat pump not heating.
E035 and E01: high pressure switch
The high pressure switch trips when the refrigerant side cannot shed its heat into the water. CTC lists low or stopped flow, a weak or undersized pump, air in the pipes, a clogged condenser and closed valves. General engineering knowledge adds limescale or magnetite sludge in the condenser; a heat pump powerflush may be part of the fix. Check valves are open, then leave the rest to an engineer.
E152: four-way valve
E152 points to a reversing valve fault or pipes wrongly connected to the EcoAir. It is an installer check, especially after recent pipework changes.
E040 and E041: brine alarms (ground source)
E040 is low brine flow, often air in the ground collector soon after installation. E041 means the incoming brine is too cold, so the loop sizing needs checking. Both need an engineer.
E052 to E055: phase faults
E052, E053 and E054 mean one of the three supply phases is missing, and E055 means the compressor is turning the wrong way, usually because two phases are swapped. You can check for a tripped breaker, but swapping phases is electrical work for a qualified electrician or engineer only.
E057 and E058: motor protection
These report high or low compressor current. CTC says to reset once and call the installer if it returns, and on older units the matching E03 is most often a lost phase or supply fault. Repeated trips can point to the issues in our heat pump compressor problems guide.
Sensor alarms
A sensor alarm means a sensor is disconnected, short-circuited or reading out of range; the full list below shows which sensor each code covers. Most clear on their own once the sensor is fixed, which is an engineer's job.
Communication and electrical alarms
E027, E063, E021 and E086 report lost communication between the circuit boards, E024 is a blown internal fuse and E087 is a driver fault. General engineering knowledge says a loose or damaged cable is a common cause of the comms codes. Reset once, and if it returns, quote the exact code when you call us.
Which error code might you see in common situations?
The situation often narrows down the code, and the first check is usually simple. CTC has no dedicated water pressure code in the lists we used, so low pressure tends to show up as a flow alarm.
| Scenario | CTC codes you may see | First check |
|---|---|---|
| Cold snap, iced outdoor unit | E135, E211, E163, then E218 or E219 if they repeat | Clear loose snow from around the unit; read our tips on heat pumps in cold weather |
| Losing pressure or low pressure | E211, E216, E217, E035 | Read the gauge; see heat pump losing pressure |
| Radiators lukewarm | E216, E217, E035 | Radiator valves open, pressure normal |
| No hot water | E137, E138, E139 (EcoTank sensors), E026 | Note the exact code shown |
| After a power cut | E052 to E055; info messages I012, I013, I030, I031 | Check breakers, then wait: info messages are not faults |
| Unit noisy or fan not spinning | No code for a rasping noise (air in the system); E163 if ice is not clearing; E01 on older units | Look for ice or debris round the fan |
| After a service or filter clean | E216, E217, E211, E035, E152 | Check valves were reopened and pressure restored |
How do you reset a CTC heat pump?
On an EcoZenith or EcoLogic controller, press the Reset Alarm button on the display. Some alarms clear by themselves once the fault has gone, and sensor alarms reset automatically when the sensor is fixed.
On older EcoAir 105 to 111 units with their own display, press OK and the down arrow together. The phase sequence alarm E09 cannot be cleared from the display. On an EcoPart i600M, E002, E007 and E015 are cleared by changing the system definition in the Installer menu, which is best left to your installer.
Critical freezing and flow alarms are different. They need an acknowledgement in the installer's coded settings, and after the fourth critical alarm the heat pump locks until an installer attends. Resetting again and again without fixing the cause can lead to exactly that lock-out, so one reset is enough before you call for help.
CTC error code list
This list covers the codes in CTC's EcoZenith i255 controller manual, the EcoPart i600M start guide and the older EcoAir 105 to 111 manuals. Code meanings can differ between controllers and software versions, so check your own manual too.
| Code | Meaning | Who should fix |
|---|---|---|
| E002, E007, E015 | EcoPart i600M sensors: external boiler (B9), buffer tank (B6), boiler (B10) | Engineer or installer |
| E003, E005 | Brine in and brine out sensors | Engineer |
| E010 | Compressor type unknown | Engineer |
| E013 | Expansion valve control fault (EVO off) | F-Gas engineer |
| E021, E027, E063, E086 | Communication errors between circuit boards | Engineer |
| E024 | Internal fuse blown (F1 or F2) | Engineer |
| E026 | Heat pump in alarm mode | Homeowner check, then engineer |
| E028 to E032 | Sensors: HP in, HP out, outdoor, primary flow 1 and 2 | Engineer |
| E035 | High pressure switch tripped | Homeowner check, then F-Gas engineer |
| E036, E037, E043, E080 | Sensors: high pressure, discharge, low pressure, suction gas | F-Gas engineer |
| E040, E041 | Low brine flow, low brine temperature (ground source) | Engineer |
| E044 to E050 | Compressor stops: high temperature, evaporation and expansion valve faults | F-Gas engineer |
| E052 to E054 | Supply phase 1, 2 or 3 missing | Homeowner check, then electrician or engineer |
| E055 | Incorrect phase sequence | Electrician or engineer |
| E057, E058 | Motor protection, high or low current | Engineer |
| E061 | Max thermostat (F10) tripped | Engineer |
| E074, E075 | Room sensors 1 and 2 | Homeowner check, then engineer |
| E087 | Driver fault | Engineer |
| E088, E109, E117 | Driver variants, including Driver: Offline (source text unclear, check your manual) | Engineer |
| E135, E211 | Risk of freezing, low flow in defrost | Homeowner check, then engineer |
| E137 to E139 | Sensors: differential thermostat, EcoTank lower and upper | Engineer |
| E152 | Four-way valve fault or wrong pipe connections | F-Gas engineer |
| E163 | Defrost maximum time exceeded | Homeowner check, then engineer |
| E216, E217 | Flow temperature difference, charge pump flow | Homeowner check, then engineer |
| E218 to E221 | Repeat of E135, E211, E216, E217 after four alarms (heat pump locked) | Engineer |
| E01, E02 (older EcoAir) | High and low pressure switch | Homeowner check, then F-Gas engineer |
| E03 (older EcoAir) | Motor protection | Engineer |
| E04 to E06, E08, E10, E11 (older EcoAir) | Hot gas, return, outdoor, primary flow and defrost sensors | Engineer |
| E07 (older EcoAir) | High compressor temperature | F-Gas engineer |
| E09 (older EcoAir) | Incorrect phase position | Electrician or engineer |
Where can you find the official CTC manual?
CTC publishes its manuals as PDFs on its own website, and alarm lists sit in the controller manual rather than the outdoor unit manual. These are the documents this guide draws on.
- CTC EcoZenith i255 installation and maintenance manual (alarm messages)
- CTC EcoAir 400 installation and maintenance manual
- CTC EcoAir 600M installation and maintenance manual
- CTC EcoPart i600M startup guide
- CTC EcoAir 105 to 111 installation and maintenance manual (older units)
Need help with a CTC heat pump fault?
Yes, we can help: we repair CTC heat pumps across the UK, from first diagnosis to the finished fix. Our engineers are F-Gas certified, so they can handle refrigerant faults as well as flow, sensor and electrical problems, and we offer same-day visits where we can. Every repair comes with our 12-month guarantee.
If a code has left you without heating, our emergency heat pump repair team can prioritise your call. For anything less urgent, arrange a heat pump repair at a time that suits you.
Many of the codes in this guide, especially the flow and freezing alarms, come down to dirty filters, low pressure or sludge. Regular heat pump servicing catches these early, and our cover plans are worth a look if you want ongoing support. You can also read more about the heat pumps we work on.
Call us on 0333 041 5130 or get in touch online.
Frequently asked questions
Does a CTC error code void my warranty?
No, a code on its own does not affect your warranty. What can affect it is unqualified work on the unit or missed servicing, depending on the terms your installer gave you. Check those terms before booking anyone, and keep records of every repair.
What is the difference between an E-code and an I-code on a CTC controller?
E-codes are alarms that point to a fault. I-codes are information messages, such as I013 for a compressor start delay or I012 when electric heating is limited for two hours after power returns. Most I-codes need no action and clear on their own.
Can I see CTC error codes on my phone?
The codes always show on the controller display, which is the most reliable place to read them. Whether you can also see them remotely depends on your controller model and how it was set up. Your installer or the controller manual will confirm this.
Does a motor protection or high temperature code mean the compressor has failed?
Not usually. Codes such as E057, E058 and E044 often come from a supply problem, a lost phase or poor water flow that makes the compressor work too hard. An engineer will test the supply and flow before looking at the compressor itself.
How long does a CTC heat pump repair take?
Many faults, such as a sensor, a blocked filter or a flow problem, can be fixed on the first visit. Repairs needing CTC parts or refrigerant work can take longer if a part has to be ordered. We will tell you what to expect once the fault is diagnosed.
