Answer first
The everyday target should be high enough to provide the agreed usable hot water after mixing at outlets, but unnecessarily high storage temperatures can reduce efficiency.
The design must also include a safe legionella-control strategy, often using periodic higher-temperature operation with an immersion heater or supported heat-pump cycle. Do not disable it without technical advice.
MCS design requires suitable cylinder capability at design conditions
View sourceHomes in the demonstration project needing a new thermal store
View sourceHot water and hygiene operation should be explained at handover
View sourceAsk FLO about hot-water design or settings
Share the property, current heating and the question holding up your decision. FLO will explain what to check next without pushing you into a survey.
Stored hot water changes the routine
A heat-pump cylinder stores energy for showers, baths and taps. The usable quantity depends on cylinder volume, storage temperature, incoming mains temperature and mixing at the outlet.
Tell the designer about high-flow showers, large baths and simultaneous use. A generic cylinder size may not match the household.
Higher temperature has an efficiency cost
The compressor works across a larger temperature lift when producing hotter water. That can reduce COP compared with low-temperature space heating.
Use planned water-heating windows and avoid repeated manual boosts unless demand requires them. The installer should explain normal recovery time.
Keep the hygiene strategy intact
Stored-water systems need a documented approach to hygiene. This can involve a periodic high-temperature cycle and the immersion heater.
The controller should show when that occurs. Frequent unexplained immersion operation is different from a deliberate scheduled cycle and deserves checking.
If hot water runs out
Record the timing, number of uses, cylinder temperature and whether a boost was requested. Check normal user settings before changing safety parameters.
The issue may be demand, schedule, sensor position, cylinder sizing, recovery or a fault. Give the installer evidence rather than simply raising every setpoint.
What to read next
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Questions people also ask
Should I set the cylinder to 60°C every day?+
Not automatically. Follow the commissioned everyday target and hygiene schedule for the specific system.
Why does the immersion heater run?+
It may support a scheduled hygiene cycle, emergency backup or a manual boost; the controller and handover should explain which.
Will a heat pump fill a bath?+
Yes when the cylinder and recovery are sized for the household’s demand.
Evidence used for this answer
Figures are explained in context and links go to the independent source. Prices, tariffs, scheme rules and standards can change, so check the source again before making a financial or technical decision.
- MCS heat-pump design standardTechnical requirements for heat loss, equipment selection, domestic hot water and system design.
- MCS domestic heat-pump guideConsumer guidance covering design, installation, controls, handover and maintenance.
- Energy Systems Catapult: home surveys and installation reportEvidence from 742 installations, including radiators, cylinders, survey constraints and typical installation duration.
- Energy Saving Trust: the most efficient way to run a heat pumpGuidance on weather compensation, longer run periods, setbacks, radiators, hot water and smart energy use.