Map the control system
Start by identifying every device that can request, stop or alter heating. A hydronic system may have:
- heat-pump controller
- outdoor temperature sensor
- room sensor or thermostat
- weather-compensation curve
- zone valves and wiring centre
- TRVs
- DHW cylinder sensor
- immersion or supplementary-heater control
- manufacturer app or internet gateway
- electricity-tariff automation
- solar or home-energy-management control
Write down which device has authority over space heating, room temperature, DHW, schedules and backup heat. A thermostat display can look like the main controller while only opening a zone valve. An app may change a target but still depend on a separate physical sensor and controller.
Keep the installer’s hydraulic and control schematic with the settings record. The control arrangement must preserve minimum water flow, active volume and any pump overrun required by the heat pump.
If the owner account depends on an installer login, transfer or add owner administration during handover. Record how the system operates without internet access.
Weather compensation
Weather compensation maps outdoor temperature to a requested heating flow temperature. Colder weather produces a higher requested temperature and milder weather a lower one.
The curve is intended to match the building’s changing heat loss while avoiding unnecessarily hot water. Lower water temperature can improve heat-pump performance, provided the emitters still deliver enough heat for every room.
Different manufacturers expose the curve in different forms:
- two outdoor and flow-temperature points
- slope and offset
- a numbered curve
- a design temperature plus room target
- an adaptive or learned curve
Do not copy a curve number from another brand or property. The same displayed number may represent a different relationship and the homes may have different emitters, heat loss and design conditions.
The commissioned record should show the selected design outdoor temperature, design flow temperature, warm-weather behaviour and any minimum or maximum limits. The design flow temperature is the cold-weather endpoint. It should not normally be forced as a fixed year-round setting.
Checking and adjusting the heating curve
First check that the system is operating in the intended weather-compensated mode. A fixed flow-temperature setting, aggressive third-party thermostat or permanent manual override can prevent the curve from governing normal operation.
If the home is consistently too warm or cool across a range of outdoor conditions, an owner adjustment to the curve or room target may be appropriate under the manufacturer’s instructions. Record:
- date and outdoor conditions
- old value
- new value
- rooms affected
- reason for the change
Leave enough time for the building fabric and emitters to respond. A heavy building or underfloor-heating system can take much longer to settle than the air around the room sensor.
Where rooms behave differently, inspect the room-by-room issue before raising the whole curve. A cold room may have an undersized or unbalanced emitter, restricted flow, trapped air, a closed valve or a heat-loss input that differs from the property. Raising the curve for one room can overheat the rest of the house.
Do not change installer safety limits, compressor envelopes, pump minimums, defrost settings or electrical protections as though they were comfort controls.
Room influence and thermostat modes
Weather compensation uses outdoor temperature. Room influence also uses an indoor sensor to adjust the requested water temperature or curve. A conventional thermostat may instead stop heating when its room reaches the setpoint.
These behaviours are not equivalent:
- pure weather compensation follows the outdoor relationship without direct room correction
- room influence or load compensation adjusts the request according to indoor temperature
- on/off room control enables or disables a heating demand
- adaptive control may alter the curve or schedule from observed response
Product terminology varies. Check the manufacturer description for the installed controller.
The room sensor needs a representative position. Direct sun, a stove, kitchen gains, a draught or a nearby radiator can cause it to govern the whole system from an unrepresentative temperature.
If an on/off thermostat frequently stops the heat pump, review the weather curve, emitter balance and control mode with the installer. Frequent cycling can also result from low system volume, closed zones or the unit’s minimum output, so the thermostat should not be assumed to be the only cause.
Schedules and setback
A setback lowers the room-temperature target during selected periods. It is different from switching the heating off completely.
The best schedule depends on:
- building heat loss and thermal mass
- emitter size and water temperature
- heat-pump capacity at the outdoor condition
- available recovery time
- occupancy and comfort
- tariff periods
- supplementary-heater behaviour
Steady operation at a low flow temperature can suit a regularly occupied home and a modulating heat pump. A modest setback may suit a property that is empty or where a lower sleeping temperature is preferred. A tariff-led schedule may deliberately move some heating into a cheaper period.
Deep setback can require the heat pump to recover at high output, possibly during colder outdoor conditions. A system selected close to the design heat load has limited spare capacity on the coldest days. Recovery may therefore take longer than a former boiler schedule.
There is no universal setback temperature or recovery time. Start from the commissioned schedule, make a small recorded change and observe whether the home reaches the required temperature without persistent high flow, supplementary heat or loss of comfort.
An “off” period in one controller may mean frost protection only, while another controller continues at a reduced target. Confirm the installed definition before using it for a long absence.
Zones, TRVs and water flow
Closing zone valves or TRVs reduces the emitter area connected to the system and can also reduce water flow or active system volume.
Use the hydraulic schematic and the heat-pump manufacturer’s requirements to check how minimum flow and water volume are maintained in every permitted zone state. The exact arrangement is specific to the installed unit, emitters and pipework.
After changing an owner-accessible valve or zone schedule, watch for low-flow warnings, increased cycling, uneven room temperatures or unexpected pump and valve noise. Restore the recorded setting and contact the installer if the change affects normal operation.
Do not force valves or alter bypass, pump or buffer settings without a competent review of their commissioned hydraulic function.
DHW settings
DHW normally runs as a separate cycle at a higher water temperature than space heating. The heat pump may pause space heating while it reheats the cylinder.
Record:
- normal cylinder target
- sensor location and displayed temperature
- DHW schedule
- heat-pump cut-off or maximum for the cycle
- immersion or supplementary-heater role
- hygiene programme
- priority over space heating
- manual boost method
The displayed cylinder temperature can differ from water at the outlet because the sensor measures one position and stored water stratifies. A higher stored temperature also changes scalding risk, usable mixed-water volume and standing loss.
Do not disable a hygiene programme or safety control to save energy without a competent review of the cylinder and building’s water-hygiene strategy. Equally, unexplained frequent immersion operation should be investigated rather than accepted as normal.
Schedule DHW around actual use and recovery. A tariff may make one period cheaper, while an ASHP (air source heat pump) may operate more efficiently during warmer outdoor conditions. The financially best time is specific to the tariff, system and household.
Immersion and supplementary electric heat
An immersion heater can heat the cylinder directly. A separate supplementary heater may support space heating, frost protection, commissioning or emergency operation. Each has a control purpose and electrical cost.
Identify:
- installed heater ratings
- automatic enable conditions
- manual boost
- emergency mode
- hygiene use
- meter or controller reporting
An immersion can usefully provide hot water when the heat pump is unavailable. Leaving a manual boost permanently enabled can also bypass the intended heat-pump operation.
For space heating, repeated supplementary-heater use may indicate an intentional design condition, a restrictive control setting, a fault or inadequate heat-pump output. Check the design and event history before disabling it. Frost and defrost protections are not discretionary tariff controls.
Tariffs, solar and batteries
A time-of-use tariff may reward preheating the building or cylinder during selected periods. This can reduce cost even if the heat pump uses more electricity than it would under a purely efficiency-led schedule.
Keep the objectives separate:
- lowest electricity use
- lowest bill
- lowest grid carbon
- highest use of on-site PV
- comfort and hot-water availability
The cheapest schedule can change when tariff terms change. Do not embed an old rate window in several controllers and assume it remains correct.
A home battery can supply some heat-pump demand or charge from the grid. Check its maximum power, usable energy, reserve and conversion loss. If the battery cannot support the heat pump, immersion and other loads together, its controller may import or limit output.
PV output varies. Solar can still contribute to DHW or daytime heating, but an annual PV total does not prove that energy is available during a particular heating period.
Monitoring the result
Useful monitoring distinguishes:
- heat-pump electrical input
- supplementary or immersion input
- delivered space-heating and DHW heat where metered
- flow and return temperatures
- outdoor and room temperatures
- compressor run time and starts
- DHW cycles
- tariff periods
An app’s estimated heat output or COP (coefficient of performance) may be useful for trends. Check its measurement boundary and method before comparing it with calibrated heat and electricity meters, a bill or another system.
SCOP covers a defined seasonal method. A short period COP can move substantially with outdoor temperature, flow temperature, DHW, defrost and measurement timing.
Look for consistent relationships rather than judging the installation from one mild day. Relevant patterns include rising flow temperature without improved comfort, high electricity use from a backup heater, repeated short runs, rooms that remain cool and DHW cycles much more frequent than actual use suggests.
Changing owner-accessible settings
Before changing a setting:
- Save the current value and control mode.
- State the problem being addressed.
- Check for faults, closed valves or a schedule override.
- Change one owner-accessible parameter.
- Allow the building to respond under relevant conditions.
- Record comfort, flow temperature and energy behaviour.
- Keep or reverse the change.
Avoid changing the weather curve, zone schedule and room target together. If the result improves, it will be unclear which change caused it.
Use the installer or manufacturer where the required change enters a protected menu or alters hydraulics, refrigerant operation, electrical protection or safety. Provide them with dates, weather, settings and observed symptoms rather than only a monthly bill total.
Settings and records to keep
Maintain a settings sheet with:
- controller and firmware versions
- weather-compensation mode and curve
- flow-temperature limits
- room influence or thermostat mode
- room targets and schedules
- zone and TRV arrangement
- DHW target and schedule
- immersion and supplementary-heater settings
- pump and valve configuration
- tariff or external-control link
- app ownership and service contacts
Add dated changes underneath rather than overwriting the commissioned baseline. If a software update or service visit changes the behaviour, the record will show which settings should be checked.
Keep the heat-loss report, emitter schedule and hydraulic schematic beside it. Control changes can improve operation only within the capacity of the installed unit, emitters and pipework.