Problem: Intermittent Running

When a flush valve in a gravity-flow toilet leaks, it causes the toilet to run intermittently. To remove a defective tank ball, a traditional flush-valve design, shut off the water and unthread the ball from the lift wire. Run a finger around the valve seat to check for mineral buildup or pitting. If the valve seat is not pitted but feels rough, scuff it with a scouring pad, then install a new tank ball.

Watch the tank ball fall onto the valve seat during several flushes. If it lands off-centre, adjust the lift-wire guide to the right or left.

A flapper valve is an inexpensive fix for a leaky tank-ball flush valve. Buy a conversion kit and remove the old lift wire and guide. Slide the mounting collar down the overflow tube. Hook the flapper wings over the collar pegs and make sure the flapper is centred over the valve seat. Then, attach the flapper chain or ribbon to the flush lever.

A pitted valve seat cannot be repaired, so you'll need to replace the valve or install a replacement seat.

To replace a flush valve or leaking spud (tank-to-bowl) gasket, you'll need to remove the tank. Drain the tank and use a long screwdriver and adjustable wrench to remove the brass bolts at the bottom of the tank. Lift the tank off, turn it upside down on the floor and use large pliers to remove the jamb nut that holds the valve in place. Then, clean the area around the tank hole. Install the new flush valve with the valve offset oriented away from the fill valve. Coat the new gasket with before mounting the tank on the bowl.

Problem: Continuous Running

If the toilet runs continuously in a faint trickle, look to the fill valve - in this case, it's a ball cock, a common valve that uses a float mounted on an arm to shut the valve when the tank water has reached the correct level. Remove the diaphragm screws and look for sand or mineral grit around the diaphragm seat. Remove this sediment with tweezers. If the rubber diaphragm seal is worn, replace it.

In many cases it's wiser to replace the fill valve than to search for old, discontinued parts. Inexpensive plastic models are reliable and easy to install. Shut off the water, drain the tank completely and loosen the supply riser coupling nut. Next, loosen the ball cock's jamb nut. Lift the old ball cock from the tank and clean the area around the tank opening. Coat the new fill valve rubber gasket and feed its threaded shank through the tank opening. Tighten the new valve in place and connect the fill line to the top of the overflow tube. Finish by installing a new supply riser between the shutoff valve and the fill valve.

Problem: Sluggish Flush

If your gravity-flow toilet flushes sluggishly, use a stiff wire to clean mineral buildup from the siphon hole in the bowl. Ream the holes under the rim, as well.

If your pressure-assist toilet flushes sluggishly, remove the tank lid and look for water around the top of the flush-valve cartridge. If you find water, replace the cartridge. First, release internal pressure by turning off the water supply and holding the flush lever down for 1 minute. Insert plier handles into the top of the valve and back the cartridge out.

Check your owner's manual to see if lubrication is required on the O-rings of the new cartridge.

If you don't find water atop the flush-valve cartridge, assume that you have a fouled air inducer. Undo the inducer's large nut and remove the spring and poppet. Soak the poppet in vinegar a few minutes, then roll it between your fingers to remove any mineral grit. Replace the parts and turn on the water.