faulty valve?

[Steve]

I have a Y plan system. I had the hot water on earlier, but noticed the upstairs radiators (closest to valve) were getting hot, downstairs rads were noticeably slightly warm too. Its was as it there was enough flow to heat upstairs rads, but not the downstairs ones (further away).

Should this happen? Or is the valve faulty?

 

[twgas]

That is a very common symptom of a motor-valve letting-by.