Brand: DAIKIN
Category: Air Conditioning
Document Type: Manual
Language: EN
Manual for EGSQH10S18AA9W
Uploaded: April 20, 2026, 7:49 p.m.
The ground source heat pump system consists of three loops: brine, refrigerant, and water. Heat is transferred via two plate heat exchangers from the brine to the refrigerant, and then from the refrigerant to water, which is used for space heating or domestic hot water.
A brine pump and a water pump ensure flow in their respective circuits. The compressor in the refrigerant circuit increases pressure and temperature before heat exchange with water.
When the unit starts operation:
- The brine pump starts at a continuous speed.
- The inverter water pump gradually adjusts its speed to maintain the required temperature difference.
- The inverter compressor adjusts its speed to maintain the required water temperature after pressure equalization.
When domestic hot water is activated, the 3-way valve switches to the domestic hot water tank, closing the space heating side. Simultaneous operation of domestic hot water and space heating is not possible. The 3-way valve returns to space heating when the domestic hot water setpoint is reached or timers finish.
When a thermo off signal is received:
- The compressor stops.
- The brine pump operates for 45 seconds for pressure equalization before stopping.
- The water pump operates for some minutes before stopping or starting sampling.
Troubleshooting and error codes
| Trigger | Effect | Reset |
|---|---|---|
| Thermal protector Q1L is activated (temp > 92°C). | Unit will stop operating. | Power reset + reset via user interface + pressing the button on the Q1L (if activated). |
| Possible cause | Check | Corrective action |
|---|---|---|
| Air in water circuit / backup heater. | Check if all air purge valves are open. Check if air purge valves are installed on all highest points of the field installed water circuit. | Purge air out of unit and field supplied water system and BUH. Refer to the Installer Reference Guide. |
| Increased water temperature by external heat source. | Check if another heat source is installed on the same water circuit. | Correct hydraulic field circuit. Refer to the Installer Reference Guide. |
| Faulty thermal protector Q1L / hydro PCB A1P. | Check thermal protector backup heater Q1L (see page 73). | Replace thermal protector backup heater Q1L (see page 109) or hydro PCB A1P (see page 93). |
| Faulty thermistor R2T (after backup heater) / hydro PCB A1P. | Check thermistor R2T (see page 58). | Replace thermistor R2T (see page 143) or hydro PCB A1P (see page 93). |
| Faulty thermistor R1T (leaving water) / hydro PCB A1P. | Check thermistor R1T (see page 58). | Replace thermistor R1T (see page 143) or hydro PCB A1P (see page 93). |
| Faulty backup heater assy / hydro PCB A1P. | Check backup heater (see page 54). | Replace the faulty components (backup heater (see page 106) or hydro PCB A1P (see page 93). |
| Water pressure is too low | Check the water pressure on the pressure gauge. | Increase water pressure till ~2bar. Refer to the "Installer Reference Guide". Check for possible water leaks. |
| Water flow is too low. | Check the minimum water flow required for the system. Refer to "Installer Reference Guide". | Adjust system to meet the water flow requirements. |