Octopus Energy’s Cosy manual does not describe a low pressure alarm or numeric codes. It says the system should sit between 1 and 1.5 bar when cold, and that pressure often drops after warmer months, after bleeding radiators, or after the heating has been off for a while. If your gauge is low, top up carefully if you are competent. If the Hub shows a flashing red light or the pressure keeps falling, get an engineer in.
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 Octopus Cosy 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 Octopus Cosy manual for your model. Do not attempt anything dangerous or anything that could void your warranty.
What does low pressure mean on an Octopus Cosy heat pump?
Your Cosy heating circuit is sealed and full of water. Low pressure means there is less water in it than there should be, so heat does not travel round the house as it should. Octopus says low system pressure can cause the heat pump to shut down, and that a cylinder gauge reading around 1 bar or lower may mean a top-up is needed.
Here is what the Cosy user manual (version 26-1) says on the subject:
- The recommended level is between 1 and 1.5 bar when the system is cold.
- If the pressure needs topping up, the manual says to bring it back to 1.5 bar.
- Pressure most often falls after warmer months, after bleeding radiators, or after long periods without heating.
- Low pressure may stop the system spreading heat evenly, which can affect comfort and performance.
- If a room is not heating enough, check that system pressure is correct.
What the manual does not do is list a low pressure fault code, a pressure fault light or a specific app alert. It does describe the Hub: a flashing red light means a heat pump fault, and the manual says to call the helpline or email aftercare. We would not read a flashing red Hub as “low pressure” specifically, only as a fault that needs finding.
Why does low water pressure happen on an Octopus Cosy?
- A slow leak at a radiator valve, pipe joint, underfloor manifold or connection near the cylinder.
- A tired expansion vessel that has lost its air charge, making pressure rise and fall sharply.
- Air in the system, especially after drain-down or work on the pipes.
- An automatic air vent that is weeping or stuck.
- Pressure relief valve discharge, where water leaves through the drain pipe.
- Bleeding radiators without topping up afterwards.
- A faulty gauge or sensor, which can show a pressure that does not match reality.
- Radiator or TRV changes that alter how water flows.
Patterns matter. A slow, steady fall over weeks usually points to a tiny leak or a weeping air vent. A gauge that jumps up when the heating runs and drops back when it cools often points to the expansion vessel. A sudden drop after plumbing or radiator work is usually air or a disturbed joint. Whatever you find, write it down with dates, because it tells an engineer where to start looking.
What can you safely check yourself?
- Read the pressure gauge when the system is cold and note the figure and date.
- Look for leaks: drips, damp patches, stained ceilings, wet floors, and water near the cylinder and relief valve pipe.
- Check radiators and TRVs. The manual points out that a primary Pod in a room with a TRV can affect heating, so make sure it is not being starved.
- Check the Hub light. Take a photo of any red light and note whether it is solid or flashing.
- If you are competent and the gauge is low, use the filling loop as the manual describes. It is usually a small silver hose with one or two valves. Open the valve or valves slowly, watch the gauge rise, stop at the manual’s figure and close them fully. Our guide to a heat pump losing pressure explains why repeated drops matter.
- After bleeding any radiator, check the gauge and top up if needed.
What not to do:
- Do not do any refrigerant work. F-Gas certified engineers only.
- Never remove panels from the heat pump or the cylinder.
- Do not keep over-pressurising.
- Do not ignore repeated top-ups.
- Do not leave filling loop valves open once you have finished.
Remember that the manual treats a top-up as an occasional task, such as after the warmer months or after bleeding. If you find yourself reaching for the filling loop every few weeks, that is the moment to stop and have the system checked, not to keep going.
When should you call an engineer?
- The gauge falls again within days of topping up.
- The Hub is flashing red.
- Water is dripping from the relief valve pipe.
- You can see or smell dampness near pipes or the cylinder.
- Heating or hot water has stopped.
- You are not confident about the filling loop.
- The system is under warranty. Contact Octopus first so cover is not affected.
Book early. A small leak found early is much cheaper to repair than a damaged floor or ceiling, and winter appointments go quickly.
If your Cosy was installed in the last year, mention the pressure history to your installer too. They will have the commissioning figures, which are the best baseline for deciding whether your current reading is normal for your house.
How can you stop it happening again?
- Arrange a yearly check. Our annual service checklist covers pressure, the expansion vessel, the air vent and a leak check.
- Check the gauge monthly and every time you bleed a radiator. The manual says pressure often drops after the warmer months.
- Fix drips quickly. See our heat pump leaking water guide.
- If heating is poor despite normal pressure, our heat pump not heating guide covers other causes.
- Keep TRVs and valves as your installer left them.
- Keep the Octopus app up to date and note any alerts.
Other Octopus Cosy symptoms you might see with low pressure
The manual uses lights, not codes. This table covers the lights it lists plus pressure symptoms.
| What you see | Meaning per the manual | First step |
|---|---|---|
| Hub flashing red | Heat pump fault | Call Octopus or book an engineer; check the gauge |
| Hub solid red | No primary Pod found | Check Pod battery and move it within 5 m of the Hub (not a pressure fault) |
| Hub solid yellow | Lost WiFi connection | Wait for reconnection (not a pressure fault) |
| Gauge around 1 bar or lower | Octopus says a top-up may be needed | Top up carefully if competent, then monitor |
| Rooms not heating evenly | Manual links this to low pressure and TRV or Pod placement | Check pressure and radiators |
| Heat pump shuts down | Octopus says low system pressure can cause this | Check gauge and leaks; book an engineer |
Need help with low pressure on an Octopus Cosy heat pump?
UK Heat Pump Servicing engineers find the leak, check the expansion vessel and air vent and carry out heat pump repairs with a 12-month guarantee. We also offer an annual heat pump service and cover plans, so pressure problems are found early. Contact us or call 0333 041 5130.
Frequently asked questions
Does the Octopus app warn me about low pressure?
The Cosy manual says you can check for fault indications on the Hub and monitor Pod batteries in the app. It does not describe a pressure alert. Octopus’s help pages advise keeping an eye on pressure and app alerts, so watch both.
Why is my Cosy pressure lower after summer?
The manual says pressure most often drops after the warmer months. Even so, a big or repeated drop is a sign of a leak, so do not simply top up every autumn without looking.
Is a flashing red Hub light always a pressure fault?
No. The manual lists it as a heat pump fault, without naming a cause. Check the gauge, then call for help.
Can I top up straight after bleeding a radiator?
Yes, and the manual says to check the pressure after bleeding and top up if needed. Let any air settle first, then read the gauge with the system cold so the figure is accurate.
What should I do if the pressure is fine but the Hub is flashing red?
Take a photo of the Hub and note the time, then contact Octopus aftercare or book an engineer. A flashing red Hub means a heat pump fault, and pressure is only one of many possible causes.
