What do I do if I cannot reach under the pan to fit a toilet seat?

Back-to-wall and wall-hung pans hide the plumbing and, with it, the underside of the fixing holes. Some pans have blind holes that never went through. In both cases a conventional bolt-and-nut seat is impossible, and the answer is a top-fix fitting that gets its grip inside the hole rather than from a nut underneath. The trade-off is that a top-fix grips over a shorter length, so it is the fitting that loosens.

What you'll need

• A toilet seat with top-fix fittings, or a top-fix conversion kit
• A cloth and bathroom cleaner
• A screwdriver

Step by step

1. Establish that you actually need top fix.Reach under the back of the pan with a torch. If you can see and touch the underside of the fixing holes, a conventional bottom-fix seat is available to you and is the more secure option. Only go top fix if you genuinely cannot.
2. Understand the two top-fix mechanisms.An expanding plug sits in the hole and is spread against the sides by a bolt drawing a tapered plug up into it — like a rawlplug in a wall. A toggle passes through the hole, drops sideways underneath and is pulled up against the underside of the ceramic. The toggle grips better where the hole goes through; the expanding plug is the only option in a blind hole.
3. Clean the holes and the surrounding ceramic.Grit, old plastic and limescale in the hole stop an expanding plug seating evenly and are the main reason one works loose. Clean the hole out with a small brush and dry it.
4. Fit the plugs before the seat.Push the expanding plug or toggle into each hole and set it as the instructions say — usually tightening the central bolt until it grips firmly. Do this with the seat off so you can see and feel what is happening, and check both are truly solid before the seat goes on.
5. Do not over-tighten an expanding plug.An expanding plug exerts outward pressure on the china around the hole. Tightening it hard puts a wedging force into the ceramic and can crack it. Firm and immovable is correct; forcing it past that is not.
6. Fit the seat and set its position before final tightening.As with any seat, position it central and square with the fittings just nipped, then tighten. Check it closes evenly into the bowl.
7. Expect to check it, and know why.A top-fix grips over the depth of the hole rather than clamping through the ceramic, so the everyday sideways loads from someone sitting down work it loose faster than a bottom-fix. Checking it every few months and nipping it up takes seconds and prevents the wear that eventually makes it impossible to tighten.
8. If it will not stay tight, look at the plug rather than the seat.A plug that has been tightened and loosened repeatedly deforms and stops gripping. Replacement top-fix plug kits are cheap and are sold separately from seats. Fitting fresh plugs solves far more loose seats than a new seat does.

Tips

• If your pan has through-holes but they are hard to reach rather than impossible, a long-reach nut spanner or a pair of long-nose pliers often makes a bottom-fix seat possible after all — and it will stay tight much longer.
• Top-fix conversion kits let you fit a bottom-fix seat you like to a pan that needs top fix. Check the kit suits your hole diameter.
• Buy a seat with metal-cored top-fix fittings rather than all plastic. The extra cost is small and they hold their grip far better.

If it doesn't work