My heat pump recently (while in heating mode) experienced a high pressure error. I have had this happen before (but it has been quite awhile), generally because my system is an air magnet and I have to bleed it a ton if the system is opened for repairs. Usually a flip of the breaker resets it, this time it didn't. Repairman just gave the high pressure switch a tap and it reset itself. My oil furnace (backup heat) feeds into the accumulator which is just a run of the mill hot water heater with no electricity connected. This then feeds into the heat pump. The repairman said he thought the superhot water from furnace is causing the pressure to rise to high. That would of course be true if the compressor is running. But this is the same setup I have had for seven years and it rarely trips (can't remember last time) while in heating mode. It is usually in the summer, and like I said, after the system was opened for work. Second thought, the heat pump is set to 110. It can be set as high 120. As soon as the furnace water is introduced it will turn off the compressor well before it gets to even 130 degrees. I know my system has design errors but I don't think this is what is causing the problem. Any thoughts?