Hot water cylinders and ECO4: a UK household checklist (2026)

Guide by ApplyFreeBoiler.uk (Reliant Energy Solutions Ltd), a heating and insulation installer in Bury, Greater Manchester. We are not the government, Ofgem or an energy supplier.

Many UK homes still store hot water in a cylinder, heated by a boiler, an immersion heater or both. If an ECO4 survey looks at your heating, the cylinder, its controls and where it sits all affect what could be suggested. This checklist is general information from a Bury-based heating and insulation installer and does not guarantee funding.

1. Find the cylinder and photograph it

Cylinders are often in an airing cupboard, a bedroom cupboard or the loft. Photograph the cylinder, any label or data plate, the pipework around it and any insulating jacket or factory foam. Note roughly how big it is and how full the cupboard is.

2. Work out how the water is heated

Check whether the boiler heats the cylinder, whether there is an immersion heater switch nearby, or both. Note any timer or separate switch for hot water. The surveyor needs to know which system you actually use day to day.

3. Note whether it is vented or unvented

A vented cylinder is usually fed by a cold water tank in the loft. An unvented cylinder is fed directly from the mains and has extra safety valves and a pressure vessel. If you are not sure, photograph the top of the cylinder and any tanks in the loft and ask the surveyor.

4. Write down how the hot water performs

Note whether hot water runs out quickly, takes a long time to reheat, or comes out too hot or lukewarm. Record any leaks, drips from pipes outside or noises. That everyday detail is useful context for any later recommendation.

5. Ask whether a system change would remove or keep the cylinder

Some heating changes keep a cylinder, some replace it and some remove it altogether. Ask what is being considered, why, and what it would mean for the airing cupboard, the loft tank and how many taps or showers can run at once.

6. Think about showers and water pressure

Electric showers, pumped showers and mixer showers behave differently depending on how hot water is supplied. List each shower in the home and how it is fed, so the surveyor can explain whether any of them would be affected.

7. Check the controls and timer

Note where the hot water timer or programmer is and whether it still works. Ask who would show you any new hot water controls and what settings would suit how your household uses hot water.

8. Keep the cupboard safe and accessible

Clear stored items from around the cylinder before a survey or install, and do not cover valves or pipework. If you notice a leak or a valve discharging water, deal with it as a repair straight away rather than waiting for a survey.

9. Compare local delivery data

See ECO measures by council on ApplyFreeBoiler.uk, built from DESNZ Household Energy Efficiency statistics, to see how many ECO measures have been installed in your local authority area.

10. Check eligibility

Use the ApplyFreeBoiler.uk eligibility check to see whether an ECO4 heating or insulation pathway may be available for your home in England, Scotland or Wales. ECO4 is due to close on 31 December 2026.