Applicable to models: LA6MI, LA9MI, LA12MI, LA16MI
Issue: Error code H99 shown on the display.
What this means: H99 means there is poor flow of water between the house and the heat pump during the heat pump defrost cycle, so it is stopping to protect itself.
Action: Engineer will need to investigate by following the flow diagram below.
Heat pump must be safely isolated from mains supply before carrying out any work!
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.
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!
7) If all the above checks have been made, then the refrigerant should be weighed out to check the refrigerant charge is correct. If the system is correctly charged, then the liquid temperature sensor on the condensor plate heat exchanger may be misreading, triggering the fault, or the Main Water PCB (aka Indoor PCB) is misreading the sensor.
Temperature probe connection (Pins 3 & 4) on CN-TH1 to check resistance of probe
Malfunction Decision Conditions:
During anti-freezing control in defrost operation, when the refrigerant liquid temperature < 0°C.
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
• Refrigerant Liquid temperature sensor (one of three sensors on one loom)
LA6MI / LA9MI part: X-2517001
LA12MI / LA16MI part: X-2511054
• Main Water PCB aka "Indoor" PCB (part number depends on model of heat pump)
LA6MI part: X-2511031
LA9MI part: X-2511039
LA12MI part: X-2511051
LA16MI part: X-2511058
Require additional help? Please follow link below
https://glendimplexservice.freshdesk.com/a/solutions/articles/79000136321
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