Is there a pump in the area near the boiler? see link for example of what the pump looks like: https://www.amazon.co.uk/Grundfos-UPS2-15-50-130-98334549/dp/B00EW97ZM6/ref=asc_df_B00EW97ZM6/?tag=googshopuk-21&linkCode=df0&hvadid=225363222612&hvpos=1o5&hvnetw=g&hvrand=2837266163676148159&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9045888&hvtargid=pla-420153767986&psc=1
If there is, it might be faulty and need replacing.
We live on the 5th floor and I believe we have 2 pumps, one to get the water up to the 5th and one to get the water up a level higher. I can have a closer look tomorrow.
The pumps for the entire building are on the East side of Globe. They should all be working . as they were reset a few weeks ago after a power failure.
Is the pressure in the boiler at the right level? That’s another thing you might want to check.