THE SHORT ANSWER
What does the control do?
First note whether the tap continues to flow while the handle moves normally, or whether flow stops at one side. Check any visible maker/model information and compare other taps already used normally. Some named models intentionally use a different centre position; that does not apply to every mixer. Do not force the control, dismantle the tap or adjust hot-water equipment.
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Does the water stay one temperature, or does flow stop?
Use what you already know from ordinary use. A mixer that keeps running but remains hot or cold is different from a tap that has no water, weak flow, or a handle that cannot move normally. Note whether the control changes the temperature at all, whether the stream stops near one side, and whether this is one tap or several.
| What you notice | What it may mean | Useful next step |
|---|---|---|
| Water runs, but stays cold with the handle centred; turning left adds hot; the tap is identified as Hansgrohe CoolStart | This matches the maker’s described CoolStart operation. The centre position is intentionally cold for that feature. | Check the exact product information. Do not assume this control convention applies to another mixer. |
| The temperature will not change through the normal handle range on one mixer | This is a temperature-selection symptom, but does not identify a cartridge, connection or other failed part. | Note the usual handle response, model markings and any recent installation or pipework work; ask the installer, maker or plumber to identify it. |
| Flow reduces or stops as the handle moves toward one side | There may also be a flow/control issue; the observation alone does not identify the part. | Do not force the lever or dismantle the tap. Record where the change occurs and arrange assessment if it persists. |
| Several hot taps are cold but cold outlets still work | Different systems and hot-water arrangements exist. This pattern does not prove a cylinder, tank, valve or pipe fault. | Record the affected hot outlets and contact the landlord/building hot-water operator or a plumber/heating engineer as appropriate. |
| Several outlets, including cold taps, have lost water | This is a wider supply-loss pattern rather than a hot-only mixer symptom. | Check your own water supplier’s service information and use the no-water guide. |
| The water is unexpectedly very hot | Excessively hot tap water can be a warning sign in some specific hot-water systems; the tap symptom alone does not diagnose one. | Stop using that outlet, keep at-risk people away and seek prompt competent advice. Do not test it again or adjust stored-water equipment. |
| Only a weak stream or no water is present | That is a flow-volume problem rather than a temperature-selection symptom. | Use the low-flow or no-water guide for the matching check. |
Do not turn a clue into a diagnosis
The same hot-only or cold-only symptom can have different explanations depending on the exact mixer and home system. A handle position or one outlet comparison does not identify a failed internal part.
Sources
- Hansgrohe UK - Basin taps: more than just taps
- Hansgrohe UK - Spare parts & repairs - FAQ
- Drinking Water Inspectorate - Water Storage Tanks and Cisterns
- Health and Safety Executive - Scalding risk from domestic hot water systems - safety alert
- Water UK - What to do if you lose your water supply
- Thames Water - No water or low pressure
Why a mixer may seem to give only hot or cold
A single-lever mixer changes both flow and temperature through its normal control movement, but the exact design varies. A product feature can make the centred position intentionally cold; a problem beginning after fitting or pipework work is useful context for the installer or maker, not proof that pipes have been connected incorrectly.
MODEL FEATURE
A named cold-start design
Hansgrohe describes its CoolStart basin taps as supplying cold water with the handle centred, with hot water added by turning left. Use that explanation only when the exact model information confirms CoolStart.
AFTER INSTALLATION
Behaviour changed after fitting or plumbing work
For its taps where hot and cold pipelines may have been switched, Hansgrohe asks for the product number or a photo to check whether the flow can be corrected. That is a maker-support route, not a general repair instruction or a diagnosis.
OTHER POSSIBILITIES
A persistent one-tap temperature problem
If the exact model’s control design does not explain the symptom, an installer or plumber can identify the fitting and check the installation. The symptom alone is not enough to name a cartridge, pipe connection or branch fault.
MORE THAN ONE OUTLET
Several hot outlets are affected
Homes differ in how hot and cold supplies are arranged. If cold taps still work while several hot taps are cold, contact whoever manages the home’s hot-water system or a plumbing/heating professional rather than treating it as a water-company cold-supply issue.
Make a useful note without taking the mixer apart
A short, accurate description helps the person identifying the fitting. Do not repeat a test that produces unexpectedly hot water, force a stiff control, remove trim or alter a boiler, cylinder, storage tank or valve.
Note the normal control response
If the lever moves freely, note whether water continues, changes temperature or stops as the handle moves through its usual range. Do not deliberately test unexpectedly hot water.
Identify the tap if possible
Check visible maker/model markings or existing product paperwork. Compare the control pattern only with the exact product information; Hansgrohe CoolStart is one named example.
Compare ordinary outlets
If more than one tap may be affected, record which outlets and temperatures already differ in normal use. A hot-only pattern with cold outlets working belongs with the person responsible for the home hot-water system or a plumbing/heating professional.
Note timing and close the tap
Record when the change began and any known fitting or pipework work. Close the tap normally after observing it; give the model number or a clear photo to the installer, maker, landlord or plumber.
If the water is unexpectedly very hot
Do not continue checking the temperature. Stop using that outlet, keep children and anyone at risk away, and ask the landlord or a competent hot-water professional for prompt advice. The HSE warning concerns a specific rare stored-water/immersion-heater hazard; this mixer symptom alone does not show that it is present.
Sources
- Hansgrohe UK - Basin taps: more than just taps
- Hansgrohe UK - Spare parts & repairs - FAQ
- Drinking Water Inspectorate - Water Storage Tanks and Cisterns
- Health and Safety Executive - Scalding risk from domestic hot water systems - safety alert
- Water UK - What to do if you lose your water supply
- Thames Water - No water or low pressure
Who should assess the problem?
PRODUCT IDENTIFIED
The control may be normal for this model
Compare only with the exact maker documentation. If it is a Hansgrohe CoolStart model and the observed pattern matches the manufacturer description, the centred-cold behaviour may be intentional.
AFTER A RECENT FITTING
Contact the installer or maker
Give the exact product/article number or a clear photo and explain which position gives hot or cold. Hansgrohe uses those details to check its own switched-pipeline question; do not alter pipework yourself.
ONE MIXER
Ask a plumber or landlord to identify it
If a single tap still will not provide the expected temperature, provide the model, normal handle response and recent work. Request an assessment before buying a cartridge or other part.
SEVERAL HOT OUTLETS
Contact the hot-water system operator
For a rented or managed home, contact the landlord/building operator. Otherwise ask a plumber or heating engineer to identify the system and affected hot-water side.
WIDER WATER LOSS
Check your water supplier
Use this route when cold supply is also absent across several outlets or there is a wider interruption notice; a hot-only symptom is different.
Different symptoms have different guides
Use the guide that matches what the tap is doing: weak flow, no water, or a control that is stiff or will not stop the flow.
What should a quote explain?
The next step depends on whether the fitting’s normal design explains the control, whether the issue began after installation, or whether one mixer or several hot outlets need assessment. Ask for a quote that identifies the proposed work before authorising a part replacement.
ASSESSMENT
Ask what the visit covers
Confirm whether the charge includes identifying the exact mixer and checking its control/installation, or whether diagnostic time is separate.
REPAIR QUOTE
Ask what is included
Ask which compatible part or correction is proposed, whether labour and VAT are included, whether a return visit may cost extra, and whether the issue falls under recent installation/landlord responsibility. Do not buy a cartridge from the symptom alone.
SEVERAL HOT OUTLETS
Clarify who manages the system
In a rented or managed property, ask the landlord or building operator to route the hot-water issue. A hot-only pattern does not by itself establish that the water company is responsible.
Common questions about mixer taps giving one temperature
Why does my mixer tap only run cold?
First note whether water continues to flow while the handle moves normally, and whether other hot outlets work. If one mixer is affected, identify the exact model and report its control behaviour; the symptom alone does not identify a part.
Why does it only run hot?
Do not keep testing unexpectedly very hot water. Stop using the outlet, keep at-risk people away and seek prompt competent advice. If several hot taps are affected while cold outlets work, contact the landlord or hot-water system operator/plumbing professional.
Should a mixer lever in the centre give warm water?
Not always. Hansgrohe describes CoolStart as cold at the centre with hot added by turning left. Check the exact fitting documentation; this does not establish the control convention on other mixers.
Could the hot and cold pipes be switched?
That is one installation question a maker may check for its own tap after fitting or pipework work. Hansgrohe asks for its product number or a photo; the symptom does not prove that connections are reversed, and this guide does not provide a pipework adjustment.
Is a cartridge definitely faulty?
No. A temperature-selection symptom alone does not identify a cartridge or any other failed part. The exact model and installation need to be identified first.
Who do I call if several hot taps are cold?
In a rented or managed property, contact the landlord/building hot-water operator. Otherwise ask a plumber or heating engineer to identify the system. A water-company status check is relevant when cold water is also absent at several outlets or a wider interruption is reported.
Sources
- Hansgrohe UK - Basin taps: more than just taps
- Hansgrohe UK - Spare parts & repairs - FAQ
- Drinking Water Inspectorate - Water Storage Tanks and Cisterns
- Health and Safety Executive - Scalding risk from domestic hot water systems - safety alert
- Water UK - What to do if you lose your water supply
- Thames Water - No water or low pressure
EVIDENCE & ACCOUNTABILITY
Sources and review
Prepared by Plumber.org.uk with AI assistance, using the sources listed below. These sources support the explanations; they do not endorse this website.
Source-checked guide with independent editorial review and AI-assisted research. No professional plumbing review is claimed. Initial research: 2026-09-28. Updated: 2026-09-30. This is general information, not an assessment of your installation. Prices can change; confirm compatibility and the full repair quote before buying or booking.
How we research and update guides. Spotted an error? Contact us with the page address and the detail to check. This form is for general enquiries and editorial feedback, not emergency assistance.
- Hansgrohe UK - Basin taps: more than just taps
Accessed 2026-09-28. CoolStart feature text, lines 468 - 471: identified Hansgrohe CoolStart basin taps deliver cold water with the handle centred; turning the handle left brings hot water into the mix.
- Hansgrohe UK - Spare parts & repairs - FAQ
Accessed 2026-09-28. FAQ on switched hot and cold pipelines, lines 124 - 126: Hansgrohe requests the product/article number or a photo to check whether flow can be corrected in that tap.
- Drinking Water Inspectorate - Water Storage Tanks and Cisterns
Accessed 2026-09-28. “Do I have a water storage tank?” lines 34 - 38: some older properties have tank-fed cold taps; in newer homes, especially with unvented heating systems, hot and cold taps are likely supplied directly under mains pressure. Used only to establish household supply variation where multiple outlets share a symptom.
- Health and Safety Executive - Scalding risk from domestic hot water systems - safety alert
Accessed 2026-09-28. Safety alert warns that excessively hot water from taps is a warning sign on certain stored-water/immersion-heater systems and recommends seeking competent advice. Used only to support keeping clear of unexpectedly excessive hot water and not adjusting stored-water equipment.
- Water UK - What to do if you lose your water supply
“What to do if you lose your water supply”: cold kitchen tap, inside stop valve, neighbour and water-company live issue checks.
- Thames Water - No water or low pressure
Sections “Try your cold kitchen tap”, “Check your stop valves”, “Ask your neighbours”, “Check issues in your area”.