Answer first
A cylinder can stay if its coil, capacity, insulation, controls, condition and pressure arrangement suit the selected heat pump. Pipework can stay where its circuit flow and pressure drop are acceptable and its condition supports reliable operation.
Ask the quote to identify what is retained, the evidence used and any remaining uncertainty. “Existing system reused” without model data or hydraulic checks transfers design risk to the homeowner.
Cylinder heat transfer is checked at proposed temperatures
View sourcePipework is assessed as a circuit, not by diameter alone
View sourceThe Catapult installation study documented varied existing-home constraints
View sourceHave FLO assess the cylinder and pipework you already own
Tell FLO about the property, current heating and the point you need resolved. A £0 home survey can turn the general answer into a room-by-room design and written quote.
Check the cylinder data plate and arrangement
Record make, model, volume, coil specification, age and standing-loss information. The designer also needs available space, access, discharge route, immersion, sensors and controls.
A large vessel is not automatically suitable. A small coil can lengthen recovery or force higher temperatures, while an oversized vessel can add standing loss and occupy unnecessary space.
Map the heating circuits
Visible pipe size is only part of the hydraulic story. Length, fittings, branches, valves, radiator load and target temperature difference determine the required pump head and flow.
Microbore can sometimes remain on lightly loaded short branches; larger distribution work may be needed elsewhere. The calculation should guide targeted changes.
Assess cleanliness and condition
Old water systems may contain sludge, corrosion products, leaking valves or mixed materials. Cleaning, filtration and inhibitor are planned around actual condition and manufacturer requirements.
Reusing poor components to save capital can create noise, blocked strainers or service calls. Replacing sound components without evidence wastes budget and embodied material.
Put retained items under the design responsibility
The written proposal should state that retained items are part of the intended system, not customer-supplied unknowns excluded from performance. Any warranty boundary must be clear.
At commissioning, verify flow, temperature difference, cylinder recovery and control operation. The handover pack should record model details and final settings.
What to read next
Related answers and services
Questions people also ask
Can a boiler cylinder always be reused?+
No. Many require checks on coil performance, insulation, controls, capacity and pressure arrangement; some will not suit the proposed system.
Does 10mm pipe always need replacement?+
No. Circuit length, load, fittings, pressure drop and required flow decide—not diameter in isolation.
Can the answer be confirmed from photos?+
Photos and model labels help triage, but a property survey and design calculation are normally needed for a firm commitment.
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.
- Home Energy Scotland Grant and Loan: terms and eligible costsCurrent Scottish grant and loan limits, eligible heat-pump costs, application conditions and rural uplift rules.