Can someone offer an explanation for this problem?
>
> The hot tap over my bath does not work unless I first run the tap over the
> vanity nearby. It will run normally almost as soon as the vanity tap is
> turned on. The vanity tap need not be left running. Once the bath tap has
> started working it works fine until next time I need it.
>
> Is there an easy solution?
>
> Any help will be appreciated.
>
You didn't mention what brand or model of bath faucet you have, but I'm guessing it's a pressure balanced single handle, try changing the cartridge, or removing the pressure balancing spool if it's a separate unit. and replacing the spool.