Bypass valve location

Regarding the Tacosetter, I understand this is a fixed valve that sets the flow rate in the bypass, but with a visual display of the flow rate value. In effect I do have the same arrangement today with a fixed valve (but with no display) + ABV in series; so currently I am setting the fixed rate 'blind'.

Also, from what I understand, the problem of my permanently open ABV (no matter what its setting), is that there is too much pressure all the time, and this is forcing the ABV open.

Are you suggesting that:
- an almost closed fixed valve will reduce the pressure on the ABV, allowing the ABV to be set within its normal range?
- using CP1 will also reduce the pressure on the ABV?

Is this pressure made worse by the bypass pipework which Tee's off from the Flow after the motorised valves (see picture), and in such a way that it presents the lowest resistance of all the 4 paths (3 MVs & 1 bypass)?
 
IF your pump is set to fixed speed 3, 6.4M head, then then your ABV will always bypass water as the max bypass settings is 0.6 or 6m, if the ABV is still bypassing if its index setting is higher than whatever pump/mode you have selected then you have a ABV problem, either a faulty ABV or some debris is trapped underneath its seat.

A ABV must be installed before any motorized valve, ie between the flow and return otherwise it prevents it from performing one of its primary functions, providing a bypass to cool the boiler Hx when the the M.valves shut.

And yes, using CP1 will of course reduce the pressure at which the ABV opens, it will have to be set slightly lower than index 3, 3m.
Having a Tachosetter or just a manual throttling valve will not affect the opening pressure of the ABV but probably will reduce the flowrate as the Pump head increases.
 

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Thank you very much for all this insightful feedback.
It seems my first step needs to be to find out why the ABV never closes - either a faulty ABV or debris inside.
 
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