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Over the last few years we have had odds and sods changed on our aged CH system - IIRC both motorised valves.
The CH & HW loops work as they should but the rads upstairs get hot a lot quicker than those downstairs.
Also when the HW is called off and is reheated again the downstairs rads suffer as they cool down whilst the HW heats up.
All rads have been bled, pump is working ...... What else to check?
Lots to check but one common thing could be a bypass fitted that is either poorly set or just a manual one wide open.
Do a Google on central heating balancing. If someone has been meddling with the lockshield valves this could a fix.
Spooky it could be balancing but unusual to have balancing split like that between floors, usually ends up as the rads furthest from the pump.
Should the bypass valve be open/closed/half & half?
From recollection it's closed or very close to close.
No over run facility on the system if that makes any difference?
Rads downstairs take 40min to an hour to get warm - about the same time it takes for the HW cylinder to get up to temperature.
We've never touched the non TRV ends of the rads.
Lower floor rads possibly starting to sludge up, when they do get warm are they warm all over or are they a lot cooler at the bottom?Have you got a towel rail on the ground floor?
Shut off all rads upstairs and see how quick ground floor then heats up?