I have a 6 ton, water to water GeoExcel branded, Bosch manufactured HP. A few weeks ago I had a circ pump go out. I replaced it and having minor issues every since. Of course air was introduced into the system when I replaced it. I did my best to purge it but from past experience I have learned no matter how well or long you do it, there is always some left. My system is tied into the existing oil fueled furnace with baseboard heat. It has various expansion tanks, air releases, etc. in the system. So for the first few weeks I was in cooling mode. If I set the HP for say 44 or lower I would find that HP would freeze up. As the HP hit 44 degrees with no load on it, it would cycle off, then the temp would continue to plunge to say 37. I would not get a warning that anything was wrong. It would just say 37. I would know things were amiss when the house temp started to rise. I would then reverse the HP to heat, add water to the intake and bleed the output. I could hear ice breaking up and air being purged and it would run great. As I continued to try bleeding it, and hearing air escape it would turn off at 44 and only get down to 40 or so and not freeze up. Now I am in heating mode. I see the same issue when it turns off at 110 degrees. If there is no load on the HP and it hits 110 it will turn off and quickly rise to 115 or 117. So it exhibits the same behavior but of course freezing isn't an issue. But now twice this week I have seen my HP have a HP1 fault. These are what the manual says are possible causes. With my description of the events do you think it is still air in the system? If not what sounds likely? Discharge pressure too high. In “COOLING” mode: SOURCE COIL - Lack of or inadequate water flow. Entering water temperature too warm. Scaled or plugged condenser. In “HEATING” mode: LOAD COIL - Lack of or inadequate water flow. Entering water temperature too warm. Scaled or plugged load coil. Refrigerant charge. The unit is overcharged with refrigerant. Reclaim refrigerant, evacuate and recharge with factory recommended charge. High pressure switch. Check for defective or improperly calibrated high pressure switch.