An unvented cylinder service certificate is the record an engineer completes and signs after the annual service of your hot water cylinder. It comes from the person who did the work, not from a council or a scheme, and it is not the same as your installation paperwork. In England the twelve month interval comes from the manufacturer's instructions and guarantee conditions.
What is an unvented cylinder service certificate?
An unvented cylinder service certificate is the written record of the annual service on a mains pressure hot water cylinder. The engineer who carried out the work fills it in and signs it. No council, scheme or government body issues this document. In most homes it is not a separate sheet at all.
On a Megaflo, uniSTOR, Hydracyl or similar cylinder, the record sits in the Benchmark checklist at the back of the installation manual. Heatrae Sadia asks the service engineer to complete the service interval record after each visit. Vaillant asks for the Benchmark checklist to be filled in every year. Keep the manual with the cylinder, because the service history lives in that book.
- the date of the service and the address of the property
- the make, model and serial number of the cylinder
- the engineer and the business that attended
- the checks carried out and the readings taken
- any parts replaced, and any fault reported to you
Unvented cylinder service certificate or building regulations compliance certificate: which is which?
Two documents hide behind the phrase cylinder certificate, and only the service record is renewed each year. The other one is issued once, when the cylinder is installed.
| Criterion | Service certificate (annual) | Building regulations compliance certificate (one off) |
|---|---|---|
| When you get it | After every annual service, from the engineer who carried out the work | Once after installation, through the installer's self certification route |
| What it rests on | The manufacturer's service interval record and guarantee conditions | Part G of the Building Regulations 2010 and the notification rules in Schedule 3 |
| What it shows | That the safety valves, expansion vessel and temperatures were checked on that date | That the installation was notified and signed off as meeting the regulations |
| Who asks to see it | The manufacturer when you make a guarantee claim | A buyer's solicitor during conveyancing |
| If it is missing | A fresh record can be started at the next service by the engineer attending | Your solicitor or building control will ask how the work was notified |
Owners often ring about one document and mean the other, which is why the two get mixed up on a house sale. The service record says nothing about whether the cylinder was notified when it went in. The compliance paperwork says nothing about whether it has been serviced since. If you are not sure which one you are holding, our guide to the unvented hot water cylinder certificate works through each document in turn.
Is an annual unvented cylinder service a legal requirement in England?
No regulation in England sets a yearly service for an unvented cylinder in your own home. The twelve month interval comes from the manufacturer's instructions and the guarantee conditions. What the Building Regulations 2010 do govern is the installation itself.
Requirement G3 of Schedule 1 applies to any hot water storage system with no vent pipe open to atmosphere. Approved Document G, the guidance for England, says such a system may only be installed by a person competent to do so. It also requires safeguards so that stored water never exceeds 100 degrees Celsius. Water released by the safety devices has to discharge somewhere visible, without causing a danger.
For a let property, the annual duty sits in Regulation 36 of the Gas Safety (Installation and Use) Regulations 1998 as amended. In England that duty covers gas appliances, flues and pipework. A cylinder heated only by an immersion heater falls outside those gas regulations. Where a gas boiler heats the cylinder, it is the boiler that appears on the gas safety record, and our guide to landlord gas safety sets out the record and the copy deadlines.
What does the engineer check and record at an unvented cylinder service?
An unvented cylinder service covers the safety devices, the expansion vessel and the water temperatures, and the readings go on the record. Manufacturer instructions from Vaillant and Heatrae Sadia set out what the visit involves.
- all connections and joints checked for leaks
- the temperature and pressure relief valve, which opens if stored water gets too hot
- the expansion relief valve, which opens if pressure in the cylinder climbs too far
- the charge pressure of the hot water expansion vessel, reset where it has fallen
- flow rates checked, and the strainer in the pressure reducing valve cleaned
- the set temperatures, and the operation of any thermostatic mixing valve
Every item on that list is work for an engineer qualified on unvented hot water systems, because those valves and the discharge pipework are safety devices. In your own home you check boiler pressure, thermostat and programmer settings, the reset button and radiator bleeding. Water running from the tundish, the open funnel in the discharge pipe, means a valve has released, and that is a reason to call an engineer rather than wait.
The route from the valve to the tundish and out of the building has rules of its own, including the 600 mm limit and the fall on the pipe. Our guide to unvented cylinder discharge pipe regulations explains how D1, D2 and the tundish fit together.
Does a missing service record affect your cylinder guarantee?
A missed annual service can put a guarantee claim at risk, because manufacturers make servicing a condition of cover. Worcester Bosch guarantee terms require the product to be serviced each year by a competent, certified person, with the details entered in the service record. They reserve the right to ask for evidence of servicing, such as the completed record or an invoice. Vaillant treats annual maintenance by a competent person as a condition of the cylinder guarantee.
The manufacturer decides whether an individual claim is accepted, so keep the record even when the service found nothing wrong. A signed page with a date on it is worth more than a memory of a visit. Our guide on whether unvented cylinders need servicing goes further into the interval and what a skipped year means.
Lost the service record, or bought a house with no cylinder paperwork?
A fresh service record can be started at the next service, so a lost history is not the end of the matter. The engineer attending completes the service interval record in the Benchmark checklist, or issues a record sheet of their own. Nobody can write up a service that did not take place, so the history begins again from that visit. Ask the previous owner or the installing company first, because the manual often sits in the airing cupboard next to the cylinder.
A buyer's solicitor usually asks about the installation paperwork rather than the service history. That is the building regulations side of the file, and our guide on an unvented cylinder with no building regs record covers what to sort out before you sell. If your cylinder is coming up to its twelve month date, you can arrange the visit through our boiler service and repairs page.
Sources
- Approved Document G: sanitation, hot water safety and water efficiency (2015, with 2024 amendments)
- The Building Regulations 2010, Schedule 3 (self certification schemes)
- Gas Safety (Installation and Use) Regulations 1998, regulation 36
- Worcester Bosch: guarantee terms and conditions
- Heatrae Sadia: Megaflo Eco SystemReady installation manual (Benchmark service interval record)
- Vaillant: uniSTOR Pure and uniSTOR Plus installation and maintenance instructions