How to replace a toilet, from measuring up to first flush

Measure before you buy the new toilet

Most failed toilet swaps go wrong at the shop, not in the bathroom. The new pan has to meet your soil pipe where the old one did, so measure the existing toilet and check the new one's technical drawing against these figures. Our guide to choosing a toilet that fits the soil connection goes into the connector options in more detail. If you have not chosen a style yet, our guide to the types of toilets explains what each one needs behind the wall.

Under the Water Supply (Water Fittings) Regulations, a new toilet must not use more than 6 litres for a full flush. Any toilet sold new in the UK should already meet this, but check before buying from abroad or reusing an old cistern.

Tools and parts

Buy the pan connector at the same time as the toilet, once you know the outlet type, and have a spare flexible connector for the supply in case the old one will not reach.

• New toilet pan, cistern, seat and fitting kit
• Pan connector to suit the outlet and soil pipe
• Flexible tap connector or compression fittings for the supply
• Adjustable spanner, screwdrivers, spirit level and drill
• Sponge, bucket, old towels and rubber gloves
• Sanitary silicone sealant, if the pan is to be sealed to the floor
• A rag or bung to block the soil pipe while it is open

Step 1: isolate and empty the cistern

Turn off the isolation valve on the pipe feeding the cistern. It usually has a slot that you turn a quarter turn with a flat screwdriver, so the slot sits across the pipe. If there is no isolation valve, or it does not stop the water, turn off the stopcock for the house and plan to fit an isolation valve as part of the job.

Flush the toilet and hold the handle or button down so the cistern empties as far as it will. Sponge out what is left in the cistern and bail out the water in the pan. Lay towels around the base, because there is always more water than you expect.

Step 2: remove the old toilet

Undo the supply connection at the cistern inlet. On a close-coupled toilet, undo the two bolts that hold the cistern to the pan from underneath and lift the cistern off. On a low-level toilet, the cistern is fixed to the wall and connected by a flush pipe. Unscrew the pan from the floor, then rock it gently side to side to free the outlet from the connector or soil pipe.

As soon as the pan is out, stuff a rag or bung into the soil pipe to stop sewer gas and anything falling in, and remember to take it out before fitting the new pan. Clean the floor and check it is sound. A soft or rotten floor under an old toilet is a common find and needs fixing before a new pan goes down.

If the old pan outlet is cemented into a cast-iron or clay soil pipe, do not smash or chisel it out without care. Cracking the collar of an old cast-iron stack can turn a toilet swap into a soil pipe repair. This is the point where many people call a plumber.

Step 3: fit the connector and the new pan

Push the new pan connector firmly into the soil pipe, or onto the pan outlet first, depending on the connector's instructions. Offer the pan into position, making sure the outlet goes fully into the connector without being bent or stretched. Check the pan is level in both directions with a spirit level, and mark the floor fixing holes.

Move the pan aside, drill and plug the floor, then set the pan back and screw it down with the fixing kit. Tighten gradually and evenly. Ceramic cracks easily, and a pan that is overtightened onto an uneven floor may crack weeks later. A pan that moves after fitting will eventually leak at the connector, so if it is not firm, stop and deal with the floor first; our guide on a toilet pan rocking on the floor explains the causes.

Step 4: fit the cistern and reconnect the water

Fit the flush valve and fill valve to the cistern if they are not already assembled, then place the rubber doughnut washer over the flush valve outlet. Lower the cistern onto the pan and fit the bolts with their rubber and metal washers. Tighten each side a little at a time until the cistern is firm and level. Overtightening these bolts cracks cisterns and is the most common cause of water leaking between the cistern and toilet pan on a new installation.

Connect the supply to the fill valve with a flexible connector or compression fitting, and make sure the pipe is not pulling the valve sideways. Open the isolation valve slowly and let the cistern fill.

If you are keeping the old cistern but its inlet is slow or noisy, see how to replace a toilet fill valve and set the float at the same time.

Step 5: test before you seal

Check the water level in the cistern stops at the mark on the overflow, and adjust the fill valve if not. Flush several times, then look at every joint with a dry tissue: the supply connection, the cistern bolts, the doughnut washer and the pan connector. Check again after an hour and the next morning. Small drips often only show once the washers have settled.

If you seal the base of the pan with silicone, many plumbers leave a small gap at the back. That way a slow leak from the connector shows on the floor instead of soaking into the boards unnoticed. Fit the seat last.

When to get a plumber to replace the toilet

A straight swap of a close-coupled toilet onto a plastic soil pipe is a fairly contained job. It becomes more involved when the new toilet is a different shape or the pipework is old. Call a plumber if any of these apply:

• The soil pipe is cast iron, clay or lead, or the old pan is cemented in
• The new toilet's outlet does not line up with the existing soil pipe
• You are changing to a back-to-wall, wall-hung or concealed-cistern toilet
• There is no working isolation valve and the stopcock is stiff
• The floor under the old toilet is soft or rotten
• The toilet is a macerator unit or pumps to the drain
• You are moving the toilet to a new position

Book a toilet replacement

Loyal Plumbers replaces toilets, cisterns and soil connections across London and everywhere inside the M25, as a single job or as part of a bathroom refit. We run 10 vans, 24 hours a day. Call 020 4652 8585 or send an enquiry with a photo of the old toilet from the side, showing where the outlet goes, and the make and model of the new one if you have bought it. The engineer confirms what the job involves before starting.

If you are weighing up a different style of toilet, our guides to hidden toilet cisterns and macerator toilets explain what each needs behind the wall and under the floor.