Some reassurance please. I have replaced my fifteen 40 year old radiators, am still in the long and tedious process of balancing them as described in the uk.d-i-y FAQs, and will soon be in the process of upgrading the control side of things (using Honeywell S Plan). I've bought a couple of 2 port motorised valves to put on the HW and CH outlets on my standard oil boiler, but looking at them see that in spite of being 28 mm fittings, the flow aperture of the valve looks more like 15 mm. Are all these motorised valves designed the same way, and are they likely to impede the flow significantly given that I have so many radiators to heat?
TIA
Keith