On a Hitachi Yutaki, alarm 70 is the hydraulic alarm: the unit has not detected water pressure or water flow in the hydraulic circuit. Check the system pressure gauge first, and if it is low or the alarm keeps returning, book an engineer to find the leak or flow restriction.
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 Hitachi Yutaki heat pump error codes guide covers every other code.
Please read first: this is a guide only. We make every effort to keep it accurate, but manufacturers update manuals and codes differ between models and software versions, so always check the official Hitachi Yutaki manual for your unit. Do not attempt anything dangerous or anything that could void your warranty.
What does alarm 70 mean on a Hitachi Yutaki heat pump?
In the Yutaki S80 technical catalogue, alarm 70 appears in the first cycle alarm list as a hydraulic alarm, with the main factor given as water pressure or water flow not being detected in the hydraulic cycle. In plain terms, the heat pump has looked for pressure or movement in the water side of the system and found none, so it stops to protect itself.
That wording covers two situations. One is genuinely low pressure, where the system has lost water or air has collected. The other is a circulation problem, where the pressure is fine but water is not moving because of a blocked filter, a closed valve or a pump that is not running. A French installer guide describing the same code lists low flow in the water circuit, a clogged water filter and a faulty pump as causes, with the advice to check pump flow, clean the filter and confirm all valves are open.
Hitachi alarm lists are not identical across the Yutaki range, and older units used different display formats, so do not assume code 70 means the same on every model. Always confirm in the manual for your own unit. The hydraulic alarms are shown on the indoor unit and the LCD controller, while outdoor unit alarms show on the outdoor display.
On pressure figures, the Yutaki S manual we could read confirms the expansion vessel is supplied with 0.1 MPa (about 1 bar) of internal air pressure, but the preview did not show the minimum and maximum water pressure values. An installer guide from Nu-Heat says the system needs a minimum of 1 bar. We take the cautious reading and treat less than 1 bar as low until your engineer confirms the figure for your model.
Why does a Hitachi Yutaki heat pump lose water pressure?
A sealed Yutaki circuit should keep a steady pressure. When it does not, or when alarm 70 appears with normal pressure, the usual reasons are:
- A leak from radiators, valves, pipe joints, underfloor pipework or connections around the hydraulic unit.
- An expansion vessel that has lost air, so the pressure swings and the gauge sinks when cold.
- Air in the water circuit, which can stop the pump from moving water and trigger a flow alarm.
- A pressure relief valve discharging after over-pressurising, often outside where it goes unnoticed.
- Recent bleeding or radiator work that took water out of the system.
- A leaking or stuck automatic air vent.
- A blocked Y strainer or filter on the return, which Nu-Heat flags as a common cause of low flow alarms on Hitachi units.
- A closed valve or faulty circulation pump that stops water moving even though the gauge looks fine.
If the gauge is healthy but alarm 70 keeps coming back, the problem is much more likely to be flow than pressure, and that is where an engineer’s flow measurements come in.
What can you safely check yourself?
These checks need no tools and no panels removed. If you are not comfortable with any step, stop and call an engineer.
- Read the pressure gauge with the system cold. If it is below 1 bar, treat it as low and look for the cause rather than just refilling.
- Note the alarm number on the controller and whether the heating, hot water or both have stopped.
- Look for visible drips and damp patches at the hydraulic unit, radiators, valves and relief valve outlet.
- Check radiators, zone valves and isolation valves are open. A closed circuit is a classic reason for a flow alarm.
- Top up through the filling loop only if the manual allows it and you are competent, taking it up slowly and fully closing the loop afterwards.
- Check the gauge again after 24 hours. A fall tells you the loss is real.
Our guide to why a heat pump keeps losing pressure goes into the repressurising process and what a normal rate of loss looks like.
What not to do:
- Do not attempt any refrigerant work. Refrigerant handling is for F-Gas certified engineers only, and a low water pressure fault is not a refrigerant fault.
- Do not remove the outdoor unit or indoor unit panels. Live electrics, moving parts and pressurised components sit behind them.
- Do not keep over-pressurising to be safe. Pushing the gauge towards the maximum can lift the pressure relief valve and stress joints.
- Do not ignore repeated top-ups. If you need to refill the system more than once or twice a year, water is escaping somewhere and it needs finding.
- Do not open the Y strainer on a pressurised system without isolating it first. Dirty water will come out quickly.
When should you call an engineer?
- Alarm 70 returns after a reset.
- The gauge keeps falling after top-ups, or the relief valve is dripping.
- The pressure is normal but the alarm persists, which suggests a flow or pump problem.
- Heating or hot water has stopped.
- You see water leaking anywhere on the system.
Booking early matters here. A small leak caught in week one is usually a cheap fix, while months of topping up can let air and fresh oxygen into the circuit and cause sludge and corrosion.
How can you stop it happening again?
- Arrange a yearly service. The annual service checklist shows what an engineer should check, including strainer, vessel charge and gauge pressure.
- Deal with drips early. See our guide to a heat pump leaking water.
- If the water is dirty or the strainer clogs often, ask about a heat pump powerflush and a filter.
- If the system has stopped working, our guides on a heat pump not working and not heating help narrow it down.
- Check the gauge monthly and log the reading.
Other Hitachi Yutaki codes you might see with low pressure
Only the alarms we could confirm in Hitachi’s Yutaki S80 documentation that relate to the water circuit are listed here.
| Code | Meaning | First step |
|---|---|---|
| 70 | Hydraulic alarm: water pressure or water flow not detected in the hydraulic cycle. | Check the gauge and valves, then book an engineer to look for leaks, air, the strainer and the pump. |
| 75 | Freeze protection on the cold water inlet. Listed trigger: inlet water temperature below 2 °C. | Not a pressure fault, but it can appear in cold weather alongside flow problems. Leave it on and call an engineer. |
Older Yutaki units show different codes, and Nu-Heat describes a “FAUL 9” display on some Hitachi controllers as air or a blocked filter. If your display does not match this table, check the manual for your exact model.
Need help with low pressure on a Hitachi Yutaki 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 repair Hitachi Yutaki heat pumps, tracing leaks, clearing blocked strainers and checking the pump and expansion vessel so the system holds its pressure again. Our annual heat pump service catches pressure problems before they stop your heating, and we also offer cover plans if you would rather spread the cost of looking after the system. If your gauge is low or a code is showing, contact us or call 0333 041 5130.
Frequently asked questions
Does Hitachi alarm 70 mean the heat pump is broken?
Not usually. It means the unit cannot detect pressure or flow in the water circuit, which is far more often a leak, air or a blocked filter than a failed heat pump.
Why does the Yutaki stop when the pressure is low?
It protects itself because running without enough water can overheat the heat exchanger or damage the pump. Once water and flow are restored, an engineer can clear the alarm.
Can I add antifreeze or inhibitor to a Hitachi Yutaki circuit?
Ask your engineer first. The right product depends on your system and warranty, and the wrong additive can cause problems with flow and seals.
How quickly should I get it fixed?
As soon as practical. A pump running dry or with trapped air can wear faster, and a small leak turns into a bigger repair if left.
Is the Yutaki gauge on the heat pump itself?
Position varies by installation. Many are on the filling loop area or the pipework near the hydraulic unit, and your installer should be able to point it out.
