How do I tighten a wobbly toilet seat?

A seat gets more use than almost anything else in the house. Bemis, a toilet seat manufacturer, says seats loosen because of "the repetitive motion of raising and lowering the seat and cover, plus the fact that it's one of the most-used places in the house." The bolts that hold the hinges slowly work loose. Bemis also calls a loose seat "a safety concern," so it is worth fixing rather than living with.

First, make sure it is the seat that moves. Sit down and rock. If the seat slides on the bowl while the porcelain stays put, this page is for you. If the whole toilet shifts against the floor, that is a different repair. See why a toilet rocks or leans and how to fix it, and why a toilet leaks at the base if you see water around the bottom.

A quick way to sort it out takes a minute:

• Grab the back of the seat and try to slide it side to side. Movement here means loose hinge bolts or a missing washer.
• Press down on the rim of the bowl itself with the seat out of the way. If the porcelain shifts on the floor, the seat is not your problem.
• Look at the floor around the base. Cracked caulk, a stain, or a damp spot points to the toilet's seal, not the seat.
• Notice any sewer smell at the base. That also points below the seat.

Gather a screwdriver, an adjustable wrench, and pliers. Bemis cautions to use them carefully because "metal can easily scratch porcelain."

1. 1Open the hinge covers. The two plastic caps at the back of the seat snap open. Under each one you will see a bolt head.
2. 2Center the seat. Bemis says "If your seat is out of alignment, now is the time to center it on the bowl." Kohler gives the same advice: "Keep the seat straight and centered as you tighten the bolts."
3. 3Hold the nut and turn the bolt. Kohler says "It is best to tighten the bolts from the top, like a screw, holding on to the bolts if necessary." Bemis adds that if the bolts are attached by wing nuts under the bowl, you should "use your screwdriver to hold the bolt in place while manually tightening the wing nuts."
4. 4Watch the pressure. Bemis warns against overtightening because it could strip or break the bolt. Its troubleshooting guide adds that overtightening "can damage the seat or bowl."
5. 5Close the covers and test the seat.

If a bolt just spins, Bemis says "you'll need to grip the wing nut with the pliers while tightening the top of the bolt with the screwdriver." For a seat with metal bolts and nuts, Bemis says to "hold the nut in place with the wrench and then tighten the bolt with a screwdriver."

Two things are usually going on. The first is a missing or worn washer. Bemis says "if the seat still wiggles after you've tightened it, you may need to insert washers on the nut between the bolt and the underside of the toilet." Kohler's instructions for a standard seat say "If your seat comes with a metal washer and rubber washer, the rubber washer goes in-between the hinge and china." That rubber layer is what gives the seat grip on the porcelain, so check that it is still there and in the right place.

The second is the hardware itself. Bemis says its Stay-Tite fastening system works like this: "The lower portion of the nut is designed to snap off during installation, indicating that perfect tightness has been achieved." Some seats also allow adjustment. In its troubleshooting guide, Bemis says many Bemis hinges "allow for front-to-back or side-to-side adjustments," so check the instructions that came with the seat if it will not sit square.

If bolts are stripped, cracked or corroded, replace the seat or the hardware rather than forcing them. Forcing a bolt risks damaging the seat or the bowl.

Quick-attach seats. Some seats use a different system. Kohler's Quick Attach hardware works this way: "Insert the bolt through the top side of the toilet seat hinge and push the wing nut from the underside until it meets the bowl." To tighten it, Kohler says "Tighten with a screwdriver from the top. The wing nut does not need to be held while tightening." If you have this style, you can do the whole job from above, with no reaching under the bowl.

A few habits keep the seat from working loose again.

• Recheck now and then. Bemis suggests you "Regularly check the tightness of your seat to prevent future issues."
• Avoid abrasive cleaners. Bemis recommends "mild soap and water" and says to avoid "harsh chemicals or abrasive cleaners."
• Match the seat to the bowl. A seat that does not fit the bowl shape will always feel off. If you are shopping, the comfort height versus standard toilet page covers bowl height, and skirted toilets have their own considerations.

If the hardware is worn. Sometimes the bolts strip or the plastic nuts crack, and a new seat is simpler than patching the old one. Match the shape first. Standard bowls are round or elongated, and a seat cut for the wrong one will overhang or leave gaps. Check the hinge spacing, too. The two bolt holes in the back of the bowl are where the hinges anchor, and the new seat has to line up with them.

Once the new seat is on the bowl, follow the same order as above. Set it square, hold the nut, snug the bolt, and only then close the hinge covers. Manufacturer sheets are short, so read the one in the box. Kohler's, for example, spells out which washer goes where.

The seat is a DIY job. The toilet is where a plumber comes in. Call if the bowl rocks on the floor, if there is water at the base, if the toilet leaks from the tank, or if you notice a sewer smell. Those point to the wax ring, the closet bolts or the flange, and how to fix a broken toilet flange explains what that repair involves. If you are replacing the whole toilet, how to know when it is time to replace a toilet helps you decide.

Here's the short version. Center the seat, hold the nut, snug the bolt, and add a washer if it still moves. Done. Most loose seats take one pass with a screwdriver, and a seat that keeps loosening every few weeks usually has a worn washer or a stripped bolt behind it.

If the toilet itself is the problem, HQ Plumbing & Air handles toilet repair and toilet replacement across the Valley. You get a free estimate and the price up front before work starts.