Gravity fed pipework query

Been in my house two months now and thought to update my 3 way valve gravity fed pumped system. The fitting has it stands consists of a manual 3 way valve, no cylinder stat, no room stat and an old two position clock timer. going to fit mot 3way, room stat, cy stat, room sat, digital timer. Anyway my query is the manual 3 way valve is on the return lines from the heating (B) and cylinder (A) returns through boiler return (AB) so the water is pumped directly to the tank lower connector and radiators first. Is this ok? can't find anything with regards to fitting the 3 way on the return lines? hope that makes sense

From the way you haved decsribed your set up it is in fact flowing the wrong way.

The pipe into AB should be the flow from the boiler (pump goes in the flow on modern systems) with the A port being the flow to the rads and the B port being the flow to the coil in the HW cylinder. (top pipe half way up the side of the cylinder.)

That's exactly it is it ok to leave like that or should i reconfigure as i am updating, seems to work ok just not logically correct
oh and sorry just had a quick look got my A and B mixed up so
A to rads
B to coil return
AB to boiler return

I would definately advise to swap it to be on the flow and have the pump on the flow before the 3 port valve. That way it is under positive pressure and will then be plumbed as the standard industry method.

You will also have to alter the cold fill and heating expansion pipe set up as well.

The vent will T off the flow from the boiler, then the cold fill will T into the flow from the boiler (within 150mm) then the pump in the flow from the boiler, then the 3 way valve, or you could add a aerjec into the pipe work. Full instructions are included with this.

Thanks Dave, sounds good to me, will get my pipework head on