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I understand that flow rates are affected by lots of variables like pipe size and type, bends, elbows, joints and so on and that it is a complex calculation to work out the head size to get the correct pump to achieve a desired flow. The issue I have is a bit odd as my head was calculated at around 8 metres. pump then recommended was a Grundfos magna3 25 - 120 on its curve it’s is capable of 3m3/h on 11m head. it’s maximums are 9m3/h and 12m head. However I am only getting around 2m3/h and the pump is telling me I have a 12.9 metre head. the pump is set to constant curve at 100% running as an uncontrolled pump at its maximum. I have e tried all of the settings and on anything but Max get a low flow reading. the loop is described as follows starting heat source flow. 22KWH dream ASHP (needs 3.2m3/h flow rate) outlet to 22mm copper. up to attic 3m in 22mm copper. through the attic to the storage tank approx 30M 22mm copper, 2 engineered bends, 5 elbows. Down 2m into 1 elbow. Plus elbow on entry to the tank. Telford tempest 309L tank (this has 30m 32mm coils. this then runs back up and through the attic back to the ASHP on the return. again 2m up 2 elbows. 30 m run 2m down 5 elbows and 2 engineered bends. to the pump then to the ASHP about 2 m of pipe. So in all about 70 m 22mm copper. 30m of 32mm in the storage coil. 10 elbows plus 4 engineered bends. The heating and radiator loop has been disconnected and capped as part of my trouble shooting, however with it connected the flow rate did not change. So for the purpose of this question please forget the heating pipes and radiators. I am trying to get the flow on the main runs. Other pipe size on the system is about 2 metres of plastic pipe with speed fit coupling on the flow and return at a section of the run where it had to go out of the eves of the house near the ASHP as the roof design is a complex hip and valley so no gable end to come through. Removing roof tiles would be the only way to resolve this to get copper in place. so knowing that the section of plastic pipe has a slightly smaller bore than the 22mm copper is this working in copper at 20.6 bore. I am reading that the plastic pipe could be as narrow as 20mm due to the speed fit inserts. is the pipe work now all effectively reduced to that smaller bore thus loosing 0.6 mm across the entire system and creating drag to increase the head ? Is my 22mm to small? Would a second pump fix the flow, and where does it go on the system? should I increase to 28mm? Would increase greatly to 28mm on the long runs only work? would a low loss header help and what size? i have read and googled hundreds of pages on this topic and have come to some of my own conclusions already hence the numerous questions. Air in the system has also been an issue probably due to the long pipe runs. I have an air release bake on the flow as me return above the tank at the highest point. It take a long time for the air to work out of the system and the pump flow is very variable eg. From low flow to 1.6 until the due is out. Then the pump hits 2 and run silently. many advice on the air problem is also appreciated. Thank you in advance for any advice you have.