On an Ideal Logic Air heat pump, error 370 with sub-code F27 means “no water flow”, and Ideal’s own user guide tells you to check the system pressure first. If the gauge reads below 1 bar, top it up with the filling loop (only if you are confident doing so), then see whether the code clears. If it comes back, the cause is usually a blocked filter, air in the pipework or a leak, and it needs an engineer. On the outdoor unit, a flashing AE code is the matching “low water flow” error.
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 Ideal 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 Ideal Logic Air manual for your unit. Do not attempt anything dangerous or anything that could void your warranty.
What does 370 F27 mean on an Ideal heat pump?
The 370 code is a general fault with the outdoor heat pump unit, and the letter and number after it narrow it down. F27 is the one for no water flow. In plain terms, the heat pump has tried to move water around the heating circuit and the flow sensor is not seeing enough of it. The unit then stops the compressor to protect itself.
It is easy to assume F27 is purely a pressure fault, but pressure is only one possible cause. Low system pressure, a blocked strainer, trapped air, a closed valve and a failing pump can all produce the same message. That is why the user guide asks you to check the pressure first, since it is the quickest thing to rule out.
The guide gives a normal reading of 1 to 1.5 bar on the pressure gauge, and says to top up with the filling loop if it has dropped below 1 bar. If the code persists after that, it points you to your installer, because the system filter may be blocked or there may be air in the primary pipework.
On the outdoor unit itself, the maintenance manual lists AE as the “low water flow error”. The unit flags it when flow stays below the minimum for 10 seconds after the pump starts, and the compressor stops. The same manual lists 9B as a circulation pump error. Neither of these is a dedicated “low pressure” code, and Ideal does not publish a separate hydraulic low-pressure alarm for the Logic Air that we could find. The manual gives a maximum water circuit pressure of 3 bar but no minimum figure, so rely on the 1 to 1.5 bar guidance in the user guide.
One more point to keep straight: the Logic Air also has refrigerant-side pressure codes, such as A5, which is a low suction pressure error. That is a gas circuit problem and has nothing to do with the water in your radiators. It is F-Gas engineer territory.
Why does an Ideal heat pump lose water pressure?
A sealed heating circuit should hold its pressure for months. When it does not, the usual causes are:
- A small leak at a radiator valve, pipe joint, pump connection or the pressure relief valve.
- A failed or badly charged expansion vessel, which lets pressure swing and then drop.
- Air in the system that has been released through the automatic air vent, taking pressure with it.
- The pressure relief valve discharging after pressure spiked, then not reseating properly.
- Recent bleeding or radiator work, where water was released and not replaced.
- A blocked magnetic filter or Y-strainer, which causes the same F27 flow message even though pressure is fine.
- A faulty flow sensor or pump, which can report no flow when there is plenty.
- A pressure sensor or gauge fault, so the reading on screen does not match the real pressure.
Homeowners are often surprised that a blocked filter is such a common cause. Installers report that the filter mesh next to the unit is the first place to look when low flow errors appear, particularly in the first year after installation when debris is still working its way out of the pipes.
What can you safely check yourself?
- Look at the pressure gauge on the system. Note the reading, and whether it is cold or hot, as pressure rises a little when the water warms up.
- Look for visible drips or damp patches around the unit, the cylinder, pipework, radiator valves and under floors.
- Check the radiator valves and any zone valves are open, so water can circulate.
- Make sure the outdoor unit has power and is not showing any other fault on the controller’s info screen. Write down the full code, for example 370 F27.
- Only if you are competent and the manual allows it, top up slowly through the filling loop to the pressure shown in the user guide, then close it fully and disconnect it. Never leave the loop connected.
- Read our guide on a heat pump losing pressure for more on what is normal and what is not.
What not to do:
- Do not touch any refrigerant pipework or connections. Refrigerant work is for F-Gas certified engineers only.
- Do not remove panels or covers on the outdoor unit or cylinder.
- Do not keep over-pressurising the system to make the error go away. High pressure can lift the relief valve and damage components.
- Do not ignore repeated top-ups. If you are adding water more than once, something is wrong.
- Do not remove or clean the filter unless you know how to isolate it, as water will escape.
When should you call an engineer?
- The pressure drops again within days or weeks of a top-up.
- 370 F27 returns after you have restored the pressure to the right range.
- You can see water on the floor, around the unit or from the relief valve discharge pipe.
- The filter or strainer needs cleaning and you are not sure how to isolate it safely.
- The pressure gauge reads normal but the code persists, which suggests a sensor, pump or flow switch fault.
- Any refrigerant-side code, such as A5, appears.
- You have no heating or hot water.
Book early. A slow leak is much cheaper to find than a flooded floor, and a heat pump that keeps tripping on low flow is working harder than it should.
How can you stop it happening again?
- Have the system serviced every year. Our annual service checklist shows what a proper visit covers, including filters, pressure and the expansion vessel.
- Get small drips looked at straight away. Our guide to a heat pump leaking water explains where to look first.
- Have the filter or strainer cleaned at service time, particularly in a new installation, and ask whether the system would benefit from a heat pump powerflush if it is older or sludgy.
- Check the gauge monthly and note the reading, so you spot a slow decline early.
- Ask your installer to confirm the expansion vessel pre-charge and the automatic air vent were checked at commissioning. Our commissioning checklist lists what should have been done.
Other Ideal codes you might see with low pressure
These are the water-side and related codes we could verify from Ideal’s user guide and maintenance manual. Code meanings can differ between models and software, so check your own manual.
| Code | Meaning | First step |
|---|---|---|
| 370 F27 | No water flow (low flow fault) | Check the gauge reads 1 to 1.5 bar, top up if below 1 bar, then call an engineer if it returns |
| AE | Low water flow error on the outdoor unit; flow below minimum for 10 seconds after pump start | Check pressure and valves, then book an engineer to check the filter and flow sensor |
| 9B | Circulation pump error | Do not keep restarting. Book an engineer to check the pump and filter |
| A5 | Low pressure error on the refrigerant side | Switch off if advised and call an F-Gas engineer. Not a water pressure fault |
Need help with low pressure on an Ideal heat pump?
UK Heat Pump Servicing engineers find the leak, check the expansion vessel and air vent, clear blocked filters and carry out heat pump repairs with a 12-month guarantee. We also offer an annual heat pump service and cover plans, so small faults get caught before they stop your heating. Contact us or call 0333 041 5130.
Frequently asked questions
Can low water pressure damage an Ideal heat pump?
Running with too little water can stress the circulation pump and cause the unit to lock out repeatedly. The compressor is protected by the flow check, which is why you see the fault, but repeated trips are not good for any heat pump. Get it looked at rather than resetting it.
Will the heat pump restart by itself after F27?
Sometimes the unit retries once the flow returns, but if the cause is still there it will fault again. Constant restarting just hides the problem. If it has locked out more than once, book an engineer.
Is it normal for pressure to go up when the heating is on?
Yes, a small rise as the water warms is normal, because the expansion vessel absorbs it. A big jump, or water coming from the discharge pipe, points to a vessel or relief valve problem.
Does the Ideal warranty cover a pressure fault?
That depends on the cause and the terms of your warranty. Faults caused by poor installation or lack of servicing may not be covered, so keep your service records and check the paperwork that came with the unit.
How long does an engineer take to fix low pressure?
A filter clean or top-up and re-pressurise can be done in one visit. Finding a slow leak can take longer, as the engineer may need to pressure test sections of pipework.
