What is the difference between a bar valve, a concealed valve and a manual mixer?

Shower valves are usually described by how they look, which tells you nothing useful. What matters is whether there is a thermostat in there, whether the body is reachable, and whether the pipe centres are standard. The schematic drawing shows all four with their supplies, so you can match what is on your wall.

Safety

Step by step

1. Identify a thermostatic bar valve.A horizontal chrome bar on the surface of the tile, with two controls: one marked with temperature, usually with a red override button at around 38 degrees, and one for flow or for selecting outlets. Its two inlets connect to hot and cold pipes coming out of the wall. This is the most common modern arrangement and the easiest to live with.
2. Note the 150mm centres.Bar valves are made to a standard inlet spacing of 150mm between hot and cold, which is why a bar valve can generally be swapped for another bar valve without touching the pipework. The inlet elbows have some adjustment to take up small errors. This standard is genuinely useful and worth knowing before you assume a replacement means a plumber.
3. Identify a concealed valve.A plate on the tile with one or two handles and nothing else visible. The valve body is buried in the wall. It looks the best of any option and it is the hardest to service — access is through the plate if the design allows, or by opening the wall if it does not. Ask what the access arrangement is before choosing one.
4. Identify an exposed valve with a rigid riser.A valve body on the wall feeding a fixed vertical pipe up to a shower head, rather than a hose. Mechanically it is the same as a bar valve and services the same way. The riser is a rigid pipe so the head height is fixed.
5. Identify a manual mixer.One handle, one body, no thermostat. It sets a blend of hot and cold in a fixed proportion. If the pressure of either supply changes — a tap opened elsewhere, a toilet filling — the proportion changes and so does the temperature at the head. There is no maximum stop and no shut-off if the cold fails.
6. Understand what the thermostat is actually for.It is a safety device before it is a comfort one. It holds a set temperature against supply variation, it stops at a set maximum, and if the cold supply is lost entirely it shuts the hot off rather than delivering scalding water. That last behaviour is the reason a thermostatic shower sometimes appears to fail — it is protecting the person in it.
7. Work out what you can service on each.Bar valve and exposed valve: both cartridges, the inlet filters and the check valves, all from the front with the valve on the wall. Concealed valve: usually only the cartridge behind the plate, and on some designs not even that. Manual mixer: one cartridge or a pair of washers, depending on age.
8. Choose on serviceability as well as looks.A bar valve is not as elegant as a concealed one and you can fix it in twenty minutes on a Sunday. A concealed valve looks superb and, when its cartridge fails, may involve a tiler. Know which trade-off you are making before the tiles go on.

Alternatives

• Electric shower: Heats mains cold water at the point of use, so it works when the boiler does not and it is independent of the hot water system. Modest flow, and its supply is a dedicated high-current circuit — installation is an electrician's job.
• Digital or electronic shower: A processor-controlled mixing valve with a remote control panel and the mixer unit hidden in a loft or cupboard. Precise, programmable, and dependent on electronics and on manufacturer support for spares.
• Bath shower mixer: A bath tap with a diverter and a handset. The cheapest way to get a shower over a bath, and its performance is limited by the tap and the system rather than by anything you can change at the head.

Questions people ask