If you feed the hot supply in to the top of a matrix & the return cooler water out of the lower level, you will aid circulation by the thermo-syphonic effect
Unfortunately Inlet and Outlet are exactly the same level.
Oh dear, not well designed, this makes you totally reliant on the efficiency of the water pump and the frictional losses of the hoses and matrix core, you may have a partial air lock in the heater - try a bit of a power flush with a hosepipe via the feed pipework
