I have H98 error on my LA-MI heat pump. What does this mean?

Modified on Wed, 22 Feb, 2023 at 10:01 AM

Applicable to models:  LA6MI, LA9MI, LA12MI, LA16MI


Issue:  Error code H98 shown on the display. No heat, compressor is stopped.  


What this means: H98 means the heat pump has stopped due to a refrigerant high pressure overload protection.

Action: Engineer will need to investigate by following the information below:

Heat pump must be safely isolated from mains supply before carrying out any electrical work! 

Refrigerant High Pressure errors are most likely caused by insufficient flow of water between the heat pump and the property. If the water cannot flow correctly, the heat cannot escape the condensor inside the heat pump quickly enough, causing the refrigerant temperature & pressure to increase until the High Pressure error H98 is shown.

Note that only F-GAS qualified engineers are legally allowed to work on the system if they are leak checking, connecting to the refrigerant system or changing refrigerant components! 

When trying to diagnose the cause of the error, it may be necessary to reset the error to allow the heat pump to attempt to run each time. To do this:

1)    When the heat pump attempts to run, check that the flow rate around the system is sufficient. Check this in HEAT mode and TANK (hot water) mode. Press "MODE" on the keypad to toggle between just HEAT or just TANK mode. 

We supplied a taconova flow checker in the LA-MI heat pump kits. The red leaver on the meter is squeezed and the bottom of the float indicates the flow rate. 

The flow rate should be close to or greater than:

46.6 litres per minute for LA16MI

35 litres per minute for LA12MI

26.6 litres per minute for LA9MI

16.6 litres per minute for LA6MI

If the flow rate falls too low, the flow switch inside the heat pump activates and the controller shows H62 flow fault.

2)    Isolate the heat pump from the mains supply and close both flow & return water isolation valves on the rear of the heat pump. Check the inline strainer on the return pipe to the heat pump as per pictures below. If there is dirt or debris in this, the flow rate will be slowed down.

3)    Purge all air from the pipework. The circulation pump cannot push against air, only water. If the pump encounters an airlock, the flow rate drops off and the flow error can occur. Power flushing may be needed. Ensure the heating water system pressure is around 1.0 to 1.5 bar. If the pressure is too low, top up using the filling loop (installer supplied item). The circulation pump may struggle to circulate the water if the pressure is too low.

4)    Ensure the circulation pump speed switch is set to max (speed III). This is housed inside the heat pump unit in the garden, bottom right hand corner. Isolate the heat pump from the mains supply before removing the heat pump cover to access the pump.

LA6MI / LA9MI Pump performance:

LA12MI / LA16MI Pump performance:

5)    Ensure the 2x two-port valves are actuating correctly. If they move too slowly or not fully, then flow rates can drop at the point of changeover & cause the H62 error. This is tested by pressing the MODE button on the keypad to toggle between just HEAT or just TANK mode. If H62 occurs on changeover, one of the valves is sticking or is slow to move across.

6)    The system should be plumbed as per our hydraulic diagram. Hydraulic configurations deviating from this design may cause unforeseen flow issues. Note the sprung loaded bypass on the diagram. If thermostatic / zone valves all close on the heating circuit, the sprung loaded bypass must be set to ensure flow of water can continue. 

7) If all of these have been checked and not found to be the issue, then the root cause may be the High Pressure Sensor or Main Refrigerant PCB, or possibly a system overcharged with refrigerant if it has had recent work done to it.

When running and an external refrigerant gauge is connected to the high side of the system, if the H98 error occurs and the system is still below 40 Bar, then it either a faulty High Pressure sensor, or a Faulty Main Refrigerant PCB.

Note that only F-GAS qualified engineers are legally allowed to work on the system if they are leak checking, connecting to the refrigerant system or changing refrigerant components! 

Malfunction Decision Conditions:

During operation of heating, when pressure 4.0 MPa (40Bar) and above is detected by outdoor high pressure sensor.



Possible parts, depending on engineer diagnosis:

• Horstmann 2-port valve 

(Horstmann number F228m) no longer supplied by us but enquire with Horstmann or local plumbers merchant.

• Circulation pump
LA6MI / LA9MI part: X-2511029

LA12MI / LA16MI part: X-2511049

• High Pressure Sensor (all models) part: X-2511012

• Main Refrigerant aka "Outdoor" PCB (part number depends on model of heat pump)
LA6MI part: X-2511024
LA9MI part: X-2511038
LA12MI part: X-2511044
LA16MI part: X-2511057 

Require additional help? Please follow link below


Was this article helpful?

That’s Great!

Thank you for your feedback

Sorry! We couldn't be helpful

Thank you for your feedback

Let us know how can we improve this article!

Select at least one of the reasons
CAPTCHA verification is required.

Feedback sent

We appreciate your effort and will try to fix the article