Dirty water in underfloor heating loops - how big a job to drain/clean them?

[bozor]

Hi, I have been noticing my underfloor heating taking longer than usual to heat up. Decided to take a look at the manifold and noticed the water in all the loops looking a bit worse for wear:

View attachment Screenshot 2020-05-01 at 10.32.32.png

While not super urgent right now, I think I should get that sorted out in the near future. How big a job would this be for someone, an hour, half a day, a day?

Thanks in advance!