Range from the cheapest replacement of a toilet float valve £50 (Plumbforce Direct Ltd based in W1U) to the dearest replacement of a float valve £100 (London Emergency Plumbing Ltd based in W10).
Comparing plumbers estimates for replacing a toilet float valve in the cistern tank gives you an idea of who will be better value but the best way to compare costs is to get actual quotes.
What to do - Get rates and quotes to replace a toilet float valve in NW8 by posting a job with HaMuch and we will send it to plumbers in NW8.

"My toilet makes a horn noise after flushing. I have the valve, but I was unable to replace it myself, because flushing only empties half of the cistern. So that may also need looked into. "
NW6
"Toilet in basement no longer refills, so won't flush. I believe the issue to be an internal fill valve issue or blockage. The pipe goes behind drywall so hard to identify the exact fault. Just looking for quote at this stage. "
W1S