wrote:
Hi,

I moved into a new house 5 months ago and the downstairs rads never get
hot, whilst the upstairs ones get warmish. It's an 'open' system that's
around 15 years old and I don't know if inhibitor was used correctly.

Where's the pump, is it nearest the upstairs rads or the downstairs rads? If
the pump is nearest the upstairs rads it might be that the lock shield
valves on the upstairs rads are fully open or open too far so that they are
hogging the hot water and there is not enough pressure for hot water to
reach the downstairs rads. In that case all the rads MAY need balancing. But
that doesn't explain why the upstairs ones are only warm if their control
valves are fully open. What happens to the upstairs rads when you turn the
pump up to 3 and turn the control valves on all the downstairs rads
completely off? Do the upstairs rads get hot?