A bath shower mixer tap looks like the easy swap: one fitting that fills the bath and runs a handset. Then the first shower runs at a trickle, or a combi cuts out, and the tap gets the blame. Most of the time the tap is fine. The pressure behind it, or the heat output of the boiler, is the real limit.
Quick answerYes, a bath shower mixer tap can work with a combi boiler, but check pressure and flow first. The Aqualisa Central, Uptown and Downtown list a 0.2 bar minimum, so they suit tank-fed and mains-fed homes. On a combi, boiler output limits flow, not the tap. Whatever you fit, the handset must keep a gap above the bath water.
Does a bath shower mixer tap work with a combi boiler?
Usually yes. A combi delivers hot water at mains pressure, which is far above the 0.2 bar these taps need. The catch is volume, not pressure. Browse the bath and shower mixer tap range with that in mind: a tap can open and pass water at low pressure and still feel poor if the system cannot supply enough flow.
A 0.2 to 5 bar rating tells you the tap will flow at low pressure and cope with high. It does not tell you the shower will feel good. That depends on flow.
Pressure, not boiler type, decides what you can fit
Plumbers sort supplies into two groups. Low pressure is gravity fed: a loft tank feeds a hot cylinder, and pressure comes only from the height of the water. High pressure is mains fed: a combi or unvented cylinder takes water straight from the street.
Many shower valves list a higher minimum and will not run properly on a tank. The Aqualisa Central, Uptown and Downtown list 0.2 bar, and Aqualisa calls the Central suitable for both low and high pressure systems.
How much head does 0.2 bar actually need?
Every metre of water height gives about 0.098 bar. So 0.2 bar needs about 2 m between the water level in the cold cistern and the tap outlet. A cistern 2.4 m above the bath rim gives roughly 0.235 bar before pipe friction, a thin margin.
- Measure from the water level in the cistern, not the cistern base, down to the tap outlet.
- Multiply the height in metres by 0.098 to get bar.
- Allow for long runs and tight elbows. Aim comfortably above 0.2 bar, not just on it.
- Below 0.2 bar, a mixer tap is the wrong tool. Look at a pumped or electric shower.
Trade tipShort on height? Measure the real pressure at the tap first, because hidden pipework takes pressure off the figure on paper.
On a combi, the boiler is the limit
A combi heats water as it flows, so heat output caps the flow. Take a 24 kW boiler heating cold water from 10°C to 45°C, a 35°C rise. Divide the power by 4.186 kJ per litre per degree and by 35°C. The answer is about 9.8 litres a minute.
Compare that with the listings. The chrome Central, Uptown and Downtown pages quote 70.5 to 78.85 litres a minute, which is what the tap can pass, not what a boiler can heat.
Worked example: an 80 litre bath at 9.8 litres a minute takes about 8 minutes, and only if the boiler holds full output.
Watch outDo not size a combi bath fill by the tap's headline flow rate. The tap passes far more water than the boiler can heat.
The taps in stock and what their listings say
Prices and stock below were checked on 4 November 2026. Every Aqualisa tap in the table showed low stock, not sold out. The Aqualisa bath shower tap range also has a Central deck filler.
| Tap | Pressure range | WRAS on listing | Price (inc VAT) |
|---|---|---|---|
| Aqualisa Uptown Chrome, CB.BSMT.20 | 0.2 to 5.0 bar | Yes | £190.77 |
| Aqualisa Central Chrome, CT.BSMT.CH | 0.2 to 5.0 bar | Yes | £199.40 |
| Aqualisa Downtown Chrome, DT.BSMT.CH | 0.2 to 5.0 bar | No | £208.97 |
| Aqualisa Downtown Matt Black, DT.BSMT.MB | 0.2 to 5.0 bar | Pending | £245.71 |
| Aqualisa Midas 110 HP/Combi, MD110BSM | Not stated | Not stated | £439.60 |
Uptown, Central and Downtown are two-hole, deck-mounted taps with dual levers. The Midas 110 is the one to look at for a combi, because its listing says high pressure and combination boiler systems. Pressure figures come from the product pages and from Aqualisa.
Watch outThe Downtown Chrome listing says WRAS approved: No, the Matt Black says Pending, and Uptown and Central say Yes. If the job needs a WRAS approved fitting, confirm the exact model before ordering.
The hose rule: keep a gap above the bath water
In a home, a bath is typically a fluid category 3 risk. If the handset can drop below the water line and the supply dips, bath water can be drawn back into the clean supply. Schedule 2 of the Water Supply (Water Fittings) Regulations 1999 requires backflow protection that is appropriate to the highest fluid category.
RuleThe handset must keep a tap gap above the bath spill-over level, or the supply needs a double check valve.
Water Regs UK sets the gap for fluid category 3 at 20 mm for connections up to 15 mm. It says a double check valve is typically used in a home when that gap cannot be kept or the outlet can be submerged. A single-flow mixer, where hot and cold meet inside the tap, also needs single check valves on its supplies.
Watch the toilet too. A handset hose that can reach a toilet or bidet is treated as a higher risk, fluid category 5, so the hose has to be restrained or shortened.
Where bath shower mixer installs go wrong
- Unbalanced supplies. Hot from a tank and cold from the mains will not match in pressure, so the mix swings.
- No scald protection. The Uptown, Central and Downtown listings do not say they are thermostatic. That matters if children or guests use the bath.
- Forgetting the waste. Waste is not supplied with the Uptown, Central or Downtown.
- Wrong hole count. They need two tap holes, so a one-hole bath needs a different fitting.
- Hose length assumed. The Central and Downtown Chrome listings give the hose as 1.25mm, which looks like a typo for 1.25m. Confirm the real length before you plan the holder.
Buyer's checklist
- Measure head or pressure before choosing a valve, and write it down.
- Confirm the model is WRAS approved if the project needs it.
- Check whether it is thermostatic if children or guests use the bath.
- Plan the tap gap or a double check valve so the handset stays clear of the water.
- Order a waste and check the tap hole spacing.
If the numbers say a mixer tap will not work, an electric shower heats its own water from a cold feed and ignores the boiler altogether.
Related reading
FAQs
Yes, if the pressure at the tap reaches the listed minimum. The Aqualisa Central, Uptown and Downtown list 0.2 bar, which needs about 2 m of head from the cistern water level, before pipe losses. Measure on site first, because short heights and narrow pipes cut the real figure.
Yes. A combi supplies mains pressure, comfortably above 0.2 bar. The real limit is heat output, since a 24 kW combi heats about 9.8 litres a minute through a 35°C rise. The Midas 110 listing specifically mentions high pressure and combination boiler systems.
You need adequate backflow protection. If the handset cannot keep the tap gap above the spill-over level, or can be submerged, a double check valve is typically used in a home. A single-flow mixer also needs single check valves on its supplies. Check the installation manual.
The KT listings for the Uptown, Central and Downtown do not say they are thermostatic; they describe dual lever control. If scald protection matters, ask before ordering or choose a thermostatic valve. The Midas 110 listing mentions safe touch controls and a temperature override button.
No. The Uptown, Central and Downtown listings, including the Matt Black, show waste supplied: No, so you need to buy one separately. They are deck-mounted taps that need two tap holes in the bath, so check the hole spacing against the tap before you order.
On the KT listings, the Uptown and Central say WRAS approved: Yes, the Downtown Chrome says No, and the Downtown Matt Black says Pending. The Midas 110 does not state it. If the job needs approved fittings, confirm the exact model with us before ordering.
Find the right bath shower mixer tap
Compare in-stock Aqualisa, Grohe and Ideal Standard bath shower mixer taps, or apply for a trade account.
Shop bath shower mixer tapsApply for a trade account
