My bunglow has had a loft conversion (bedroom) but no heating installed. Existing boiler is in ktchen (rear of property) and flow/return are routed up into what remains of loft space, descending into airing cupboard in centre of property. From there a pump/3 port valve provide hw and ground floor heating to 7 rads.
I have fitted one rad in upstairs bedroom plus small towel rail rad in ensuite, both with TRV and bypass for when both shut off.
Question is where to tap into heating system? My logic says down stream of the pump and then back into the return, both in airing cupboard. This would mean that I will have tee'ed off in effect before all the groundfloor rads. Is this OK?
My first thoughts are to ask how much higher the header tank base is above the top of your new radiators as filling them may be a problem?
There is no requirement for the tap off to be at any particular position in a circuit providing the rad is connected between flow and return. Of course, you must ensure it is actually in the heating circuit after the pump and 3PV not in the boiler feed side.
My last point is to ask why you believe a radiator bypass is required??? A "Y" plan heating system with a 3PV does not require any extra bypass as the cylinder coil and hall radiator are quite sufficient. Fitting others may reduce the whole system efficiency and depending how you have plumbed it, may stop some rads getting hot at all. Is it fitted with an extra lockshield valve?