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Unvented cylinder service checklist
An annual service record for an unvented hot water cylinder. Scan the data label and record the capacity and heat source, then the incoming pressure, pressure reducing valve setting, expansion vessel pre-charge and stored temperature. Check the temperature and pressure relief valve, expansion relief valve, energy cut-out, tundish and discharge, strainer and leaks, with a detail box for each defect. Record the result, parts needed, whether the service record was completed and the next service. Every question is listed below, and you can fill the live form in on this page.
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What is checked in an unvented cylinder service?
An unvented cylinder service checks the incoming mains pressure and pressure reducing valve, the expansion vessel pre-charge, that the temperature and pressure relief valve and expansion relief valve open and reseat, that the energy cut-out works, that the tundish is visible and the discharge pipe safe, and cleans the line strainer. Approved Document G says unvented systems should have at least two independent safety devices as well as the thermostat, and the Building Regulations require precautions so that the stored water can never exceed 100°C.
Last updated . Facts checked by the SiteSurvey team on 17 October 2026 against requirement G3 in Schedule 1 to the Building Regulations 2010 (hot water supply and systems), Approved Document G (2015 edition with 2024 amendments): unvented hot water storage systems and Hot Water Association: unvented hot water storage cylinder servicing guide.
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Every question in the unvented cylinder service template
An unvented hot water cylinder (G3) annual service: cylinder and heat source, inlet pressure, expansion vessel charge, relief valves, energy cut-out, tundish and discharge, temperature setting and the next service. 3 sections and 46 questions. Follow-up questions and guidance appear only when an answer calls for them, so the person on site never sees the ones that do not apply.
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Details you only enter once
Add this form to a project in SiteSurvey and it fills in what the project already knows, so nobody on site retypes it and every form on the job uses the same names. Anything filled in can still be changed.
- Project: the project name
- Client: the project's customer
- Site: the site, when the form is opened for a space or a product
- Site address: the site address, from the space or the project
Cylinder
- ProjectShort answerFills in from the project name
- ClientShort answerFills in from the project's customer
- Site*Short answerFills in from the site, when the form is opened for a space or a product
- Site addressShort answerFills in from the site address, from the space or the project
- Service date*Date
- TimeTime
- Engineer and G3 qualification*Short answer
- Cylinder make and model*Short answer
- Scan the data labelScan a label: serial number, model number
Optional. Scan the label or tag to capture its numbers.
- Capacity (litres)Number
- Heat sourceChoose one
- Boiler (indirect)
- Immersion heater (direct)
- Heat pump
- Solar and boiler
- GuidanceBuilding Regulations requirement G3(3): a hot water system with a storage vessel must stop the stored water ever exceeding 100°C, and any discharge from safety devices must be safely conveyed to where it is visible. Approved Document G says an unvented system should have at least two independent safety devices as well as the thermostat, and advises choosing an installer with the right skills, for example one registered with a competent person scheme. The Hot Water Association's servicing guide recommends a service every 12 months, and regular servicing is usually a condition of the manufacturer's warranty.
Checks
- Incoming mains pressure (bar)Number
- Pressure reducing valve setting (bar)Number
- Expansion vessel pre-charge (bar)Number
- Pre-charge the manufacturer specifies (bar)Number
From the cylinder's installation and servicing instructions or the vessel label.
- Pre-charge against the specification (bar)Worked out by the formShown when “Expansion vessel pre-charge (bar)” is answered and “Pre-charge the manufacturer specifies (bar)” is answered
- Pre-charge correct for the system?Yes or No
- Stored water temperature (°C)Number
- Stored temperature against 60 °CWorked out by the formShown when “Stored water temperature (°C)” is answered
- CheckStored below 60 °C. HSE's HSG274 Part 2 says hot water should be stored at least at 60 °C to control legionella. Record the reason and how the risk is controlled, for example a scheduled high-temperature cycle on a heat pump.Shown only when the answers above make it relevant
- Temperature and pressure relief valve operated and reseatsChoose one
- OK
- Defect
- What is wrong?Short answerShown when “Temperature and pressure relief valve operated and reseats” is “Defect”
- Expansion relief valve operated and reseatsChoose one
- OK
- Defect
- What is wrong?Short answerShown when “Expansion relief valve operated and reseats” is “Defect”
- Energy cut-out (non self-resetting) testedChoose one
- OK
- Defect
- What is wrong?Short answerShown when “Energy cut-out (non self-resetting) tested” is “Defect”
- Tundish visible, discharge pipe and termination safeChoose one
- OK
- Defect
- What is wrong?Short answerShown when “Tundish visible, discharge pipe and termination safe” is “Defect”
- Pipe from the valve outlet to the tundish (mm)Number
Discharge pipe D1, measured with a tape.
- Vertical drop below the tundish before the first bend (mm)Number
Discharge pipe D2, measured with a tape.
- D1 against 600 mmWorked out by the formShown when “Pipe from the valve outlet to the tundish (mm)” is answered
- D2 drop against 300 mmWorked out by the formShown when “Vertical drop below the tundish before the first bend (mm)” is answered
- CheckApproved Document G (paragraphs 3.54 and 3.56) says there should be no more than 600 mm of pipe between the valve outlet and the tundish, and the D2 pipe should have a vertical section at least 300 mm long below the tundish before any elbow or bend. Record what was found and the fix.Shown only when the answers above make it relevant
- Line strainer cleanedChoose one
- OK
- Defect
- What is wrong?Short answerShown when “Line strainer cleaned” is “Defect”
- No leaks or signs of dischargeChoose one
- OK
- Defect
- What is wrong?Short answerShown when “No leaks or signs of discharge” is “Defect”
- Checks with a defectWorked out by the form
- Safety device defectsWorked out by the form
- WarningA safety device has a defect. Never bypass the energy cut-out or relief valves: replace the faulty device before the cylinder is used.Shown only when the answers above make it relevant
- Photos of the cylinder, valves and tundishPhotos
Result
- Result*Choose one
- Safe and serviced
- Serviced, parts needed
- Unsafe: left off
- Parts and work neededNotesShown only when the answers above make it relevant
- Benchmark or manufacturer's service record completed?Yes or No
- Next service dueDate
- Customer nameShort answer
- Customer signatureSignature
- Completed by*Short answer
- SignatureSignature
See it filled in
A completed unvented cylinder service report, made by SiteSurvey from a fictional site visit: every answer, the photos, the guidance that applied and the sign-off, ready to send as a PDF.
Unvented cylinder service FAQs
Is an annual service required?
The Hot Water Association's servicing guide recommends a service every 12 months by a suitably qualified engineer, and in most cases regular servicing is a condition of the manufacturer's warranty. The form records whether the Benchmark or manufacturer's service record was completed, and the next service date.
What does G3 require?
Requirement G3(3) says a hot water system with a storage vessel must prevent the stored water exceeding 100°C, and convey any discharge from safety devices safely to where it is visible. Approved Document G says an unvented system should have at least two independent safety devices as well as the thermostat, such as a non self-resetting energy cut-out and a temperature relief valve.
What if a safety device fails?
The form warns never to bypass the energy cut-out or relief valves, and to replace a faulty device before the cylinder is used. Record the result as unsafe and left off if needed.
Why does the tundish need to be visible?
Approved Document G says any discharge should be visible at the tundish, which should be in the same space as the cylinder. If it is hidden, a fault can go unnoticed. The form records it as a defect with the fix.
Can I scan the cylinder label?
Yes. Scan the data label on the SiteSurvey app to capture the serial and model numbers.
Who uses this?
Plumbing and heating engineers with unvented (G3) qualifications, landlords and housing maintenance teams.
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A legionella monthly temperature log: hot and cold sentinel outlet readings, cylinder flow and return temperatures and TMV inlets, with warnings when a reading misses the HSE target.
A thermostatic mixing valve (TMV) service record: each valve with its location, outlet and type, set and measured mixed temperatures, fail-safe test, strainers and result, with a warning above 44°C.
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