Heater Flow Restriction?

So my goal it to to run my pump at the most efficient setting while keeping the pool heated and chemically balanced.  I recently replaced/upgraded my pool heater.  As the directions recommended, installed it with a bypass valve (3 Port Diverter Valve).  I noticed that when I bypass the heater, my IC40 cell will register flow with my pump set as low as 750 rpm. However, when my heater is active (not bypassed), I have to run my pump at 1550 rpm for the IC40 cell to register flow.  Is this normal operation or is there a blockage in the heater???

Automation: Pentair EasyTouch 8SC-IC40 with ScreenLogic Interface and Wireless Connection

Pump: Pentair Intelliflo VS Ultra Energy Efficient Pump

Filter: Pentair Clean and Clear Plus Cartridge Filter - 420 sq ft

Heater: Pentair MasterTemp 400K – Gas

Salt Chlorine Generator: Pentair IC40 Cell

A blockage in the heater would be there regardless if it was running or not It sounds like you are only seeing reduced flow when the heater is running. It is normal for there to be added resistance when the heater kicks on.

So your response is confusing me.  There is a blockage in the heater, or the restrictive flow is normal operation?

If there was a blockage, there would be an issue when the heater is running and when it wasn’t running. You are only having an issue when the heater is running. That means there is no blockage.