CTC does not list a dedicated “low water pressure” alarm in the manuals we checked. Loss of heating system pressure usually shows up as a low gauge reading, or as a flow-related alarm such as E211, E216 or E135 on EcoAir models. If your pressure gauge reads low, do not keep restarting the heat pump. Check for leaks and call an engineer if you have to top up more than once.
If it keeps coming back, book an engineer rather than topping up or restarting repeatedly. You can book a heat pump repair online or call 0333 041 5130, and our full CTC heat pump error codes guide covers every other code.
Please read first: this article is a guide only. We make every effort to keep it accurate, but manufacturers update manuals, and codes can differ between models and software versions, so always check the official CTC EcoLogic S manual for your model. Do not attempt anything dangerous or anything that could void your warranty.
Is there a CTC error code for low water pressure?
No, and we want to be plain about that. The CTC EcoLogic S installation manual, which covers the controller used with EcoAir and EcoPart heat pumps, lists no bar figures for water pressure and no alarm for low heating system pressure. The CTC EcoZenith i360 overview says only that system pressure will normally be around 1 bar and that the system must be refilled if the pressure is too low. It also tells you to ask your installer for the correct value.
What CTC does list are flow alarms on air-to-water models, which can be triggered when low water or air in the system reduces circulation:
- E001, Risk of freezing (EcoAir): outgoing heat pump water is too cold for defrosting. The manual says the water volume in the system may be too low, and the flow may be too low.
- E135, Risk of freezing (critical alarm): the heat pump out temperature falls below 15 °C during defrost, or the difference between in and out is more than 15 °C for over 20 seconds. The manual points to the circulation pump, dirt filter, piping and the heat pump sensors.
- E211, Risk of freezing low flow (critical, EcoAir 600 with a flow sensor): flow below 10 l/min on EcoAir 610 and 614, or 15 l/min on EcoAir 622, for over 30 seconds during defrost. The manual says to check the circulation pump, dirt filter, pipe system, pipe size and flow sensor.
- E216, HP flow temp diff (critical, EcoAir 500 and 600): a temperature difference between heat pump in and out of more than 12 °C in heat mode for over 15 minutes. The manual says to check the dirt filter, piping and circulation pump speed.
- E217, HP charge pump flow (critical, EcoAir 400): charge pump speed above 70 percent in heat mode for over 15 minutes, with the same flow checks.
Critical alarms need care. The manual says they can be acknowledged only three times, and after four alarms the heat pump is blocked until the installer is contacted. That is a good reason not to keep resetting.
CTC also has alarms named “low pressure”, and again these are not about your heating water. E043 “Sensor low pressure” is a fault with the refrigerant low-pressure sensor, either disconnected or short-circuited. E040 “Low brine flow” is for ground source units, where air in the collector is the usual cause. If the display says low pressure, check which circuit it is talking about. Any refrigerant-side fault is for an F-Gas engineer only.
Codes and wording vary between CTC products, such as the EcoAir, EcoPart and EcoZenith ranges, and between software versions. Your installation manual is the final word.
Why does a CTC heat pump lose water pressure?
- A leak at a joint, valve, pump connection or radiator.
- A failed expansion vessel that lets pressure swing.
- Air in the system, released by the automatic air vent. CTC’s manual warns that air in the system causes poor circulation.
- The safety valve discharging and not reseating. CTC suggests operating the safety valve about four times a year to keep it working.
- Recent bleeding or radiator work without a proper top-up.
- A blocked dirt filter, which cuts flow and can trigger the flow alarms above.
- A circulation or charge pump fault, with the same symptoms.
- A gauge or sensor fault, so the reading is wrong.
Low pressure and low flow are closely linked, which is why we have covered both here. A system that has lost water has less to circulate, and air that replaces it makes pumps struggle. CTC’s own wording on E001 reminds you that a water volume that is too low is a possible cause. In practice, an engineer will check the pressure first, then the dirt filter, then the pump, and only then move on to sensors.
If you have an EcoZenith or EcoLogic controller, the info message at the bottom of the touchscreen gives more detail than the flashing light on its own. A red or yellow flashing LED indicates an alarm. Take a photo of the screen before you do anything, because the engineer will want the exact wording, plus the 12-digit serial number found behind the magnetic strip on the EcoZenith.
What can you safely check yourself?
- Read the pressure gauge (manometer) and note the figure. CTC says a system will normally be around 1 bar, but ask your installer for your own value.
- Look for visible drips, wet floors and damp patches around the unit, cylinder and pipework.
- Check radiator and zone valves are open.
- Write down any alarm text and code from the display or the info message at the bottom of the screen.
- Bleed radiators only if you are confident. CTC advises bleeding the radiator system about a month after installation and at least once a year. Recheck the gauge afterwards.
- Top up through the filling valve only if the manual allows and you are competent. See our heat pump losing pressure guide first.
What not to do:
- Do not touch refrigerant circuits. Refrigerant work is for F-Gas certified engineers only.
- Do not remove panels or covers.
- Do not keep over-pressurising the system.
- Do not ignore repeated top-ups.
- Do not use the installer codes to acknowledge critical alarms repeatedly, as the heat pump will eventually block.
When should you call an engineer?
- You have had to top up more than once.
- Any critical flow alarm (E135, E211, E216 or E217) appears.
- The safety valve is dripping or you can see a leak.
- The display shows a low pressure sensor alarm such as E043.
- Radiators stay cold after bleeding.
- You have lost heating or hot water.
Book early. Four critical alarms and the heat pump blocks itself, so a delay can turn a small fault into a no-heating call-out.
How can you stop it happening again?
- Book an annual service. Our annual service checklist covers pressure, filters, the expansion vessel and pumps.
- Clean the dirt filters regularly. CTC notes that poor water flow can increase the electricity used by the circulation pump.
- Treat small drips quickly. See heat pump leaking water.
- If the heating is slow to warm up, our heat pump not working guide covers the next checks.
- Check the gauge monthly and note the reading.
Other CTC codes you might see with low pressure
These are the verified flow-related alarms from the CTC EcoLogic S manual. None is a direct low water pressure code.
| Code | Meaning | First step |
|---|---|---|
| E001 | Risk of freezing; water volume or flow may be too low | Check pressure and valves, then book an engineer |
| E135 | Risk of freezing (critical); check pump, dirt filter and piping | Do not keep resetting. Book an engineer |
| E211 | Low flow during defrost (critical, EcoAir 600) | Book an engineer to check pump, filter and flow sensor |
| E216 | Large temperature difference between heat pump in and out (critical) | Book an engineer to check filter, piping and pump speed |
| E217 | Charge pump flow (critical, EcoAir 400) | Book an engineer to check filter, piping and pump settings |
| E043 | Sensor low pressure; refrigerant-side sensor fault | Call an F-Gas engineer. Not a water pressure fault |
Need help with low pressure on a CTC heat pump?
UK Heat Pump Servicing engineers find the leak, check the expansion vessel and air vent, clean filters and carry out heat pump repairs with a 12-month guarantee. We also offer an annual heat pump service and cover plans. Contact us or call 0333 041 5130.
Frequently asked questions
What pressure should a CTC heating system be at?
CTC says around 1 bar is normal for the EcoZenith i360, but also tells you to ask your installer for the right value. We cannot give a figure that applies to every CTC model.
How often should I bleed the radiators?
CTC suggests about a month after installation and at least once a year. Bleeding lowers pressure, so check the gauge afterwards.
What does “critical alarm” mean on a CTC?
It is an alarm the heat pump treats as serious. After a set number of acknowledgements it blocks the heat pump until the installer clears it.
Should I operate the safety valve myself?
CTC says it should be turned about four times a year to check it works. If no water runs, or it keeps dripping afterwards, get an engineer to look at it.
Does poor flow raise my electricity bill?
CTC says deteriorating water flow can increase the electricity used by the circulation pump. Clean filters and correct pressure help keep running costs down.
