Unvented cylinder servicing and the G3 safety requirement
Unvented cylinders store hot water at full mains pressure rather than gravity-fed from a loft tank, which gives strong flow at every tap but relies on a chain of safety devices working correctly.
What we check first with unvented cylinder G3 servicing
Because an unvented cylinder has no open vent to atmosphere, it depends on a temperature and pressure relief valve, an expansion vessel or internal air gap, and an expansion relief valve to stop it becoming a pressure vessel under fault conditions. Building Regulations Part G3 requires these to be checked annually by someone competent to work on unvented systems, and most manufacturer warranties are void without that annual record.
What matters most with unvented cylinder G3 servicing
- G3 servicing must be carried out by a suitably qualified engineer
- Safety devices include temperature and pressure relief and expansion control
- A missing service record can invalidate both warranty and insurance cover
- Symptoms of a failing expansion vessel include weeping from the relief valve
- Unvented systems give better flow rate than gravity-fed vented alternatives
Where we deal with this
Published business details
- Based at 24 Bristol Road, Radstock, BA3 3EE
- Telephone enquiries: 07516 118198
- Opening hours: Monday to Friday, 8:30am to 5:00pm
Need help with unvented cylinder G3 servicing?
The honest position: An unvented cylinder gives excellent pressure at every outlet, but that performance comes with a genuine annual safety obligation that should not be skipped.
For gas work, use a Gas Safe registered engineer; for oil work, use an OFTEC-registered technician.
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- Retail servicingBoiler servicing for shop premises
- System cleaning comparisonPower flush vs chemical clean: clearing a sludged heating system
Services that cover this
Questions we get asked
- Is a G3 service the same as a boiler service?
- No, though they can be combined in one visit. The cylinder's safety devices are separate components from the boiler and need their own checks.
- What happens if I skip the annual service?
- Beyond the safety risk, most manufacturers will not honour a cylinder warranty claim without an unbroken annual service history.
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