Unvented Hot Water Cylinder Maintenance Checklist
Keep unvented hot water safe and compliant — expansion vessel, pressure and temperature relief valve, tundish, and discharge checks under Building Regs Part G3.
What is an unvented cylinder maintenance checklist?
A unvented hot water cylinder maintenance checklist is a structured list of the 10 preventive maintenance tasks — covering visual, functional and record-keeping checks — that keep an unvented hot water cylinder running safely and reliably. It groups routine checks by frequency, from daily inspections to annual servicing, so FM teams and building engineers can plan and evidence preventive maintenance.
Core unvented cylinder checks
- Inspect the tundish and discharge pipe route to a safe, visible termination
- Check the expansion vessel charge pressure or re-pressurise the bubble-top
- Record the service, valve tests, and vessel pressure in the log
What is an unvented hot water cylinder?
An unvented hot water cylinder stores mains-pressure hot water without a feed-and-expansion tank, delivering strong, balanced hot water to outlets. Because it is sealed and pressurised, it carries safety devices — an expansion vessel or bubble-top, an expansion (pressure) relief valve, and a temperature and pressure (T&P) relief valve discharging through a tundish to a safe location. Installation and work on unvented systems above 15 litres is notifiable under Building Regulations Part G3 and must be done by a competent (G3-qualified) person. Annual servicing of the safety devices is essential — a failed relief path on a sealed hot water vessel is a serious hazard.
This checklist is one of 25 in our plumbing and water system maintenance checklists, covering pressurisation units, booster sets, storage tanks, TMVs and water treatment — pressure, hygiene and legionella control.
Typical Unvented Cylinder maintenance checklist
A practical starting point for planned preventive maintenance. Always refer to the manufacturer's O&M manual and site-specific requirements.
Visual Checks
- Inspect the tundish and discharge pipe route to a safe, visible termination
- Inspect for leaks at the cylinder, valves, and connections
- Confirm there is no continuous discharge from the tundish (a fault sign)
Functional Checks
- Check the expansion vessel charge pressure or re-pressurise the bubble-top
- Test the expansion (pressure) relief valve discharges and reseats cleanly
- Test the temperature & pressure (T&P) relief valve operation
- Confirm stored water temperature is set safely (typically ~60–65°C)
- Check the immersion/indirect heat source and thermostat operation
- Verify the strainer and any inlet control group (PRV) are clear and set correctly
Record Keeping
- Record the service, valve tests, and vessel pressure in the log
Download the free Unvented Cylinder maintenance checklist PDF
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Typical maintenance frequency
Suggested intervals for unvented hot water cylinder maintenance. Actual frequencies should follow manufacturer guidance and site-specific risk assessments.
Annually
- •Service safety valves and check expansion vessel
- •Test T&P and expansion relief valves
- •Inspect tundish and discharge
- •Verify temperatures and thermostat
Common faults and issues
Issues to be aware of when maintaining unvented hot water cylinder equipment.
Safety and compliance notes
Key safety considerations for unvented hot water cylinder maintenance. This is general guidance only — always follow OEM instructions, statutory requirements, and your organisation's safe systems of work.
Reference standards and frameworks
- United Kingdom
- HSE ACoP L8 and HSG274 for water hygiene
- North America
- ASHRAE Standard 188 (legionellosis risk management)
Frameworks commonly referenced when planning unvented cylinder maintenance programmes. Always confirm the requirements that apply to your site and jurisdiction.
Managing Unvented Cylinder documentation with PM Assist
PM Assist helps FM and building operations teams search their O&M manuals and building drawings in seconds. Upload your unvented hot water cylinder documentation and ask questions like “What is the cylinder's stored temperature setting?” or “When was the last G3 service?” — and get source-cited answers instantly.
See PM Assist answer questions about a real unvented cylinder manual — try the live demo, no signup needed.
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Further reading on unvented cylinder maintenance
Compliance topics for unvented cylinder maintenance
Frequently asked questions
How often should an unvented cylinder be serviced?
Why is my tundish dripping or discharging?
Who can work on an unvented hot water system?
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