Regrinding a tap seat to prevent a dripping tap

A dripping tap cannot always be cured by just fitting a new washer, sometimes the valve seat has become damaged. The valve seat is what the washer closes onto when the tap is closed. The pressure of the water under the washer tries to force itself between the seat and washer and over time the water erodes the brass seat. Little channels are formed in the seat (as indicated right) which allows the water to pass between the washer and seat causing the tap to drip. This can be worse in areas with hard water.

Here we detail how to regrind a tap valve seat.

Pillar tap diagram

The small channels in a tap seat can be removed by grinding the rest of the seat down. This produces a flat, smooth seat for the washer to sit on and seal the flow of water. A seat grinder is a simple tool, they are normally supplied with different sized serrated cutters and screwed location bushes ( to position the cutter central on the tap seat).

The correct size serrated cutter for your tap will be the one that just fits through the opening, and the correct size bush is tightened in the threads which held the tap valve.

See the page dealing with changing a tap washer for the procedure to gain access to the tap seat.

1. Insert the grinder in the top of the tap, fit the thread of the bush in the screw thread and tighten it.
2. While pushing down on the handle, twist the grinder against the tap seat. Twist clockwise so that the cutter tightens on the shaft.
3. Remove the grinder periodically and look at the seat, any imperfections in the seat will stand out as dark areas. Keep grinding until the complete circle of the seat is a bright brass colour.
4. Finish with a few, full revolutions of light pressure give the seat a final polish.
5. Replace the valve (with a new washer) in the base of the tap and fit the handle - DO NOT CLOSE THE TAP.
6. Turn off all other taps which were opened.
7. Turn on the water supply to the tap and allow water to flush through it - this will remove any debris remaining in the tap after grinding the seat.