The complete guide
How to Choose and Fit a 47mm Pop Up Bath Waste Plug
The problem with a bath that will not hold water
There is a particular kind of annoyance that comes from running a bath and watching it slowly empty underneath you. You top it up with hot water, the level holds for a few minutes, then it starts creeping down again. By the time you have properly relaxed, your shoulders are cold.
Almost always, the pipework is fine. The trap is fine. The thing that has failed is the plug, and specifically the point where the plug meets the waste seat. Over years of hot water, shampoo, bath oils and the occasional scrub with something abrasive, that contact surface stops being a clean seal. Plastic plugs deform. Seals harden. Threads loosen so the plug no longer sits at the height it was set to.
That is good news, because the plug is the cheapest and easiest part of the whole assembly to change. A replacement bath pop up plug is a ten minute job for most people, and you never have to get underneath the bath.
What a pop up plug actually does
A pop up waste is different from the old chain and rubber plug arrangement. Instead of a loose stopper you drop in, the plug is permanently attached to the waste by a threaded stem. You press it, twist it or operate a lever, and it lifts off the seat to let water out. Press again and it drops back down.
The seal is made by the underside of the plug pressing against a circular seat in the waste body. For that to work, two things have to be true. The plug has to be the right diameter for the waste, and it has to sit at the right height so it makes even contact all the way round.
Diameter is fixed. A 47mm bath plug fits a 47mm waste and that is that. Height is where most of the trouble happens, because wastes vary in depth depending on the bath, the assembly and how carefully the original installer set it up. A plug that is two millimetres too high will leak. One that is too low will bottom out before it seats and leak just as badly.
This is why an adjustable chrome bath plug is worth having. The 5 to 6.5cm adjustment range on this one gives you a decent window to work with, so you can dial in the exact height your bath wants rather than hoping an off the shelf part happens to land right.
Measuring your waste before you order
Take a tape measure or a steel rule and measure straight across the circular opening in the bottom of the bath, edge to edge, through the middle. You are measuring the hole, not the plug currently sitting in it.
If you get something around 47mm, this plug is your size. UK and European bath wastes commonly land there, which is why it is the most widely stocked size. If you get something noticeably smaller, you may be looking at a basin waste rather than a bath waste. If it is much larger, you have a non standard assembly and should take the old plug with you when you shop.
One tip. Measure before you remove the old plug if you can, because once it is out it is easy to measure the plug rather than the opening and end up a few millimetres out.
Why the material matters more than you think
A bath plug lives a hard life. It is wet almost every day, it goes from cold to hot and back, it gets stood on, and it collects soap residue that is mildly corrosive over time. That is a lot to ask of a moulded plastic part with a sprayed finish.
Brass is the traditional answer. It is heavy enough to feel solid, it does not go brittle, and crucially the threads hold their shape. That last point is what keeps an adjustable plug adjustable. If the stem thread wears or deforms, your carefully set height slowly drifts and you are back to a leaking bath six months later.
The chrome plating on top does two jobs. It gives you the bright finish that matches most bathroom taps and overflow plates, and it adds a hard surface that resists the general wear of daily use. Look after it (mild cleaners, soft cloths, no scouring powder) and it will keep looking right for a long time.
Fitting it without drama
Start by removing the old plug. Most unscrew anticlockwise from the waste. If it has been in for years it may be stiff, in which case a bit of patience and a cloth for grip usually beats force. Avoid pliers directly on a chrome surface unless you have padded the jaws.
With the old plug out, clean the waste seat properly. This is the step people skip and then wonder why the new plug leaks. A build up of soap film and hair on the seat will hold the new plug just off the surface. A cloth and a little washing up liquid is enough. Run a finger round the seat afterwards to check it feels smooth.
Thread the new plug in and set it roughly in the middle of its adjustment range to start. Then run water. Fill the bath a few inches, leave it ten minutes, and see whether the level holds. If it drops, make a small adjustment (a quarter turn is often plenty) and test again. Going in small steps is faster than big guesses, because it is easy to overshoot in the other direction.
Once it holds for ten minutes, fill it properly and leave it longer. A slow seep that is invisible over ten minutes will show up over an hour.
Who this suits
If your bath has a 47mm pop up waste and the plug has stopped sealing, this is the straightforward fix. It is also a sensible thing to keep as a spare if you manage rental properties, run a holiday let, or look after a building with several bathrooms. A bath that will not hold water generates complaints quickly, and having the part on a shelf means you solve it the same day.
It suits people who are comfortable with a simple hand job and do not want to pay a call out charge for a part that threads in by hand. It is less suitable if your problem turns out to be the waste assembly itself, the overflow connection, or a joint under the bath. Those need a different part and, usually, a different set of tools.
Keeping it working
Maintenance is barely worth the word. Wipe it over when you clean the bath. Every few weeks, lift it out and clear whatever has collected on the underside and on the seat. In a household with long hair, that is where most sealing problems start.
Stay away from scouring pads, cream cleaners with grit in them, and strong bleach or acid based products. Chrome plating is hard but it is also thin, and once it is scratched through, the damage spreads. A mild washing up liquid solution does everything you actually need.
If the plug starts to leak again after a year or two, check the height adjustment before assuming the plug has failed. Thermal cycling and general use can nudge a setting out by a fraction, and a quarter turn often puts it right.
The short version
Measure across your bath waste opening. If it is around 47mm, this plug fits. It is brass with a chrome plated finish, it adjusts between 5 and 6.5cm so you can set it to seal properly in your particular bath, and it replaces only the plug rather than the whole waste.
Clean the waste seat before you fit it, set the height in small steps, and test with real water rather than assuming. Do that and you have fixed a genuinely irritating problem in about the time it takes to make a cup of tea.