Bathroom sink runs when toilet is flushed

[CAJ]

Flush upstairs toilet and sink either drips or runs til toilet is filled.
Have tried to get air out of lines by shutting off water to house to no avail.
TIA, Craig

 

[joecaption]

I'd start by checking the incoming water pressure, there's no need for it to be above 60 PSI.
If the pressure is OK then it's time for a new cartridge in your faucet.

 

[CAJ]

Check gauge coming into house?

 

[Jeff Handy]

Many modern faucets rely on water pressure to maintain their seal.

When the toilet flushes, bathroom water pressure drops a little, but that should not be enough to make the sink faucet start running.

Yes, change the faucet cartridge, that should fix it.

If it still drips, try partially closing the supply valve for the toilet, so it fills up slower.

And I think this problem would be more likely due to low incoming house water pressure, rather than too high of pressure.