Unvented cylinder servicing: what's required

Yes. Unvented cylinder manufacturers require a service every 12 months by a competent person, and their guarantees can be void without proof of it. The Building Regulations don't set a service interval, but they do require installation by a competent person and two independent safety devices. The annual service checks those devices still work, and is recorded on the Benchmark service record.

Is servicing an unvented cylinder a legal requirement?

Not as a fixed interval in law. Approved Document G, which covers hot water safety in England, deals with design, installation and commissioning. It doesn't set a servicing period. The annual requirement comes from the manufacturers, and it is written into their guarantees.

Kingspan's Albion manual says "This product requires servicing every 12 months" and warns the guarantee may be void without proof of annual servicing. Megaflo's manual says the checks should be done by a competent person on an annual basis, and lists regular maintenance and a completed Benchmark service record as guarantee conditions. Both say the manufacturer isn't liable for faults caused by lack of maintenance.

Landlords and commercial clients may have their own duties to keep equipment safe, which is a good reason to keep the service record even where the guarantee has run out.

What does the law say about installing one?

In England, Approved Document G says an unvented hot water storage system needs a minimum of two independent safety devices to stop the stored water exceeding 100°C: a non-self-resetting energy cut-out, and a temperature relief valve or combined temperature and pressure relief valve. Discharge must be visible at a tundish, which sits vertically in the same space as the cylinder, with at least 300 mm of vertical pipe below it.

Installing one is notifiable building work. If you're registered with a competent person scheme, you don't need to notify building control in advance; your scheme handles it. Otherwise you notify building control before you start. Small water heaters of 15 litres or less with the right safety devices are generally exempt from notification, unless the electrical work is notifiable.

Scotland, Wales and Northern Ireland have their own building regulations. Megaflo's manual names Technical Standard P3 for Scotland and Building Regulation P5 for Northern Ireland alongside G3 for England and Wales.

What does an annual service include?

The checks in both manuals cover the same ground: prove each safety device still works, keep the inlet clean, and confirm the expansion arrangement is right. Use the specific manufacturer's procedure for the cylinder in front of you; values such as expansion vessel pressure vary by model.

Megaflo suggests lining the cylinder service up with the boiler service, which saves the customer a second visit and saves you a second trip.

Who can service an unvented cylinder?

A competent person, in the manufacturers' words. In practice that means someone trained in unvented hot water systems, often called a G3 qualification after the Building Regulations part. One council's building control guidance says competent installers should hold a current registered operative identity card for unvented systems. Electrical checks on the immersion heater need someone competent in electrical work too.

If the cylinder is heated by a gas boiler, the boiler service needs a Gas Safe registered engineer. The cylinder service doesn't, unless gas work is involved.

What should you record and leave with the customer?

The Benchmark service record, filled in after every service. Benchmark is the industry scheme covering how heating and hot water products, including hot water storage cylinders, are installed, commissioned and serviced. The commissioning checklist and service record sit at the back of the manufacturer's manual. Kingspan says they will be needed for any guarantee claim.

Keep your own copy as well: date, cylinder make, model and serial number, the valve checks, the expansion vessel pressure, and anything you advised. A photo of the completed Benchmark page on your phone is better than nothing.

How do you keep customers coming back every year?

Remind them before the anniversary, and tell them why it matters: the guarantee. A plumbing, heating and air conditioning firm in Swindon with about six engineers raised exactly this with us: unvented cylinder servicing and service reminder intervals sat on the same list as its gas safety records. Reminders that live in an old database go stale; the gas engineers we spoke to described the same problem with gas safety reminders.

Hi customer first name,

Your hot water cylinder at address is due its annual service on due date.

The manufacturer, make, asks for a service every 12 months by a competent engineer to keep the guarantee valid. We'll check the safety valves, clean the inlet filter, check the expansion vessel and fill in the service record in your cylinder manual.

It takes about time and costs price incl. VAT. If your boiler is due too, we can do both on the same visit.

Reply with a day that suits, or call phone.

your name
company name

Send it four weeks before the due date and again a week before. If you have landlord customers, the same rhythm works for their gas safety records and the electrical reports they need every five years.

This is a summary of the rules and manufacturer guidance. For a specific cylinder, the manufacturer's manual takes priority. If you find a fault with a safety device, make it safe and follow the manufacturer's procedure.

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