Hot at the top, cold at the bottom
Sludge sits in the bottom of a radiator. Bleeding only fixes air, which collects at the top. Different symptom, different job.
Air makes a radiator cold across the top and sometimes noisy. Magnetite — black sludge — makes it cold along the bottom. Bleeding will not stir that up. A chemical cleaner might, a power flush often will, and sometimes the honest fix is a new radiator plus a magnetic filter so it does not happen again.
If only one radiator is cold and the lockshield is barely open, it may never have been balanced. We check that before we talk about flushing a whole house. Balancing is a shorter visit and a smaller bill.
A flush on a 1930s terrace with microbore and no drain point is a different price to a 1990s semi with 15mm copper. The guide price on this site is the second of those. We will tell you which building you have before we book the machine.
After any flush we dose inhibitor and show you the filter. If nobody can explain where the sludge went, you have paid for theatre.
