Taps go in near the end of a bathroom fit-out, but they are often the first thing that generates a callback. A few minutes of checks before the job starts will save you a return visit. Here is a practical rundown of the issues that catch installers out most often and how to stay ahead of them.
1. Confirm the Water System First
Mismatched tap and water system is the single most common cause of a tap-related callback. Before you look at the tap, know what you are working with.
Combi boiler (mains pressure, unvented): Hot and cold run at roughly equal pressure. Most modern mixer taps are designed for this setup. Flow rates are generally strong and you have full flexibility on tap selection.
Gravity-fed (vented, tank-fed): Cold mains pressure is typically much higher than the hot supply from the header tank. That pressure imbalance will cause mixing problems with many monobloc mixers. You will likely need a pressure-equalising valve, or a tap rated for low and unequal pressures.
Combi with low flow rate: Combination boilers vary widely. A struggling combi in an older property may not hit the minimum flow rate that thermostatic or more complex taps require, typically 1 to 2 litres per minute. Check the boiler's output spec if there is any doubt.
The fix: Check the tap manufacturer's minimum pressure and flow rate requirements before ordering. If the customer's system does not meet them, either the system needs attention or the tap specification needs to change.
2. Check Tap Hole Diameter and Spread
Basin taps are mostly designed around a standard 35mm tap hole, but not every basin follows that. Some ceramic basins, particularly imported or budget units, come with holes slightly out of spec or positioned in a way that conflicts with the tap body width.
Single-hole monobloc: Most contemporary basin mixers use a single 35mm hole. Confirm the basin spec before ordering.
Three-hole basins: Less common in modern bathrooms but still out there in traditional-style fit-outs. These need either a three-hole mixer or two separate pillar taps with a separate filler. A monobloc will not cover all three holes without a deck plate.
Deck plates: If the customer is replacing old three-hole taps with a monobloc, a deck plate is the clean solution. Worth having in the van or flagging in the quote.
Countertop basins: The tap hole position relative to the basin rim matters here. Too close to the rim and the spout will hit the side of the vessel rather than directing water into the bowl. Measure spout reach against the basin's internal diameter before the order goes in.
3. Match Tap Height to Basin Depth
The height of the tap body relative to the basin depth and rim height determines whether water actually lands where it should.
Mini basin taps have a short spout designed for shallow cloakroom basins. Fit one on a deeper basin and water hits the front wall or splashes out.
Standard basin taps are proportioned for the majority of wall-hung and inset basins at typical counter heights. The most versatile option for a standard bathroom or en suite.
Tall basin taps are designed for countertop vessel basins that sit proud of the surface. The extra height is functional, not decorative. Without it, the spout will not clear the basin rim.
If the basin and tap are being specified together, get both dimensions in front of you before the order is placed. Returning a tap because it does not clear the rim is a wasted day.
4. Pipe Centres and Flexi Lengths
Most basin mixer taps connect to hot and cold supplies via flexible hoses. Standard pipe centres on basin taps sit between 150mm and 200mm, with supply pipes usually rising through the floor or out of the wall.
Flexi hose length: Taps are often supplied with 300mm flexis. If the supply pipes terminate a long way from the tap tails, particularly on freestanding vanity units or where pipework comes from an awkward angle, you will need longer hoses. Keep a selection in the van to avoid a second trip.
Isolation valves: Every tap installation should have isolation valves on the supply pipes. If they are not there, fit them. Whoever services the installation in ten years' time will appreciate it, and so will you when something needs sorting quickly.
Bath taps: Bath fillers and bath shower mixers typically mount on the bath deck or the floor, depending on the design. Confirm whether the bath has pre-drilled holes and where they sit. Some freestanding baths come with no holes at all and need a separate floor-standing tap, which is a different product entirely.
5. Click-Clack and Pop-Up Wastes
Many basin taps come with a click-clack or pop-up waste included. It is worth checking a few things before you assume it is ready to install.
If the basin already has a waste fitted, you may have a conflict. A slotted waste is for basins with an overflow; an unslotted waste is for basins without one. They are not interchangeable.
If the basin has no overflow, you must fit an unslotted waste. A slotted waste on an overflow-free basin will not seal correctly.
Some countertop vessel basins are sold without any waste at all. Confirm what is and is not included before site day.
6. Finish Consistency Across the Bathroom
This is less a technical issue and more a professional one, but it matters to customers and it is easy to get wrong when fittings are sourced from separate orders.
Chrome from one manufacturer does not always match chrome from another. Polished chrome, brushed chrome, and satin chrome are three different things and they will not look consistent next to each other. If towel rails, shower hardware, and accessories are already specified, confirm the tap finish against those before ordering.
Matt black and brushed brass are particularly variable between manufacturers. Where everything is coming from the same range, you are fine. Where you are mixing sources, get a sample or a written confirmation from the supplier before the job goes in.
7. Bath Shower Mixers: Pressure Is Not Optional
A bath shower mixer with an integrated handheld shower needs adequate water pressure to work properly. The diverter and extra hose length create more resistance than a simple bath filler. On a gravity-fed system with a low header tank, flow through the shower head can be frustratingly poor.
Most bath shower mixers state 0.2 bar as the minimum, but in practice anything under 0.5 bar will produce a weak, unsatisfying shower. If the system is gravity-fed and the tank sits low relative to the bathroom, a pump is the right conversation to have with the customer before the tap goes in, not after the complaint comes in.
Common Callbacks and How to Avoid Them
| Issue | Cause | Prevention |
|---|---|---|
| Poor flow or no mix | Pressure mismatch between tap spec and system | Check system type and tap pressure rating before ordering |
| Spout misses the basin | Wrong tap height for basin type | Confirm body height against basin depth and rim height |
| Monobloc does not cover all tap holes | Monobloc fitted to three-hole basin | Check basin hole configuration before ordering |
| Dripping tap | Incorrect torque on ceramic cartridge | Follow the manufacturer's torque spec; overtightening cracks the disc |
| Finish mismatch across the bathroom | Chrome variation between manufacturers | Source from the same range where possible; confirm finish in writing otherwise |
| Weak shower flow on bath shower mixer | Low system pressure | Check static pressure; discuss a pump with the customer if needed |
UK Brassware is a trade-only supplier stocking a full range of bathroom taps including basin mixers, bath fillers, and bath shower mixers across modern and traditional styles. Free 48-hour delivery and 60-day returns on trade accounts. Browse the bathroom tap range at ukbrassware.co.uk.