No law in England sets a service interval for an unvented hot water cylinder. The yearly service comes from the manufacturer's instructions and warranty conditions. Heatrae Sadia calls the annual service an important requirement on its unvented cylinders, and says the work must follow the maintenance section of the installation manual. An unvented cylinder holds water at mains pressure, so the safety valves, the strainer and the expansion provision are the parts an engineer looks at. This page sets out what is checked, why manufacturers ask for it and who is allowed to carry it out.
Is an annual unvented cylinder service required by law in England?
No statute in England sets a service interval for an unvented hot water cylinder. Part G3 of Schedule 1 to the Building Regulations 2010 covers hot water supply and systems. It requires stored hot water to be held safely and discharge water to be carried away safely. It names no annual service.
What the regulations do control is the installation itself. Fitting or replacing an unvented cylinder in England is notifiable work. You either give notice to a building control body before the job, or use an installer registered with a competent person scheme who self-certifies the work. Approved Document G is the official guidance to Part G and is published by government.
So the yearly service is a manufacturer's requirement, not a legal one. That distinction matters when a warranty claim is made, because the manufacturer sets the terms.
Why do manufacturers ask for a yearly service on a Megaflo or unvented cylinder?
Manufacturers ask for a yearly cylinder service because they tie the warranty to it. Heatrae Sadia describes the annual service as an important requirement on direct and indirect unvented cylinders. The same manufacturer states that an annual service is increasingly a condition of the manufacturer's warranty.
The Megaflo range carries 30 years on the inner vessel and 2 years on the remaining components. The warranty has to be registered with proof of purchase, and servicing follows the installation manual. Glow-worm takes the same line on its Hydracyl unvented cylinders: the guarantee can fall away without evidence of annual maintenance.
Keep every service record with the cylinder paperwork. That evidence is what a manufacturer asks for if a valve, thermostat or vessel fails years later.
What does an annual unvented cylinder service check?
An unvented cylinder service is built around the safety devices and the parts that silt up. The items below follow the maintenance sections of manufacturers' manuals for Megaflo and other unvented cylinders. Every one of them is engineer work.
- Safety valves operated by hand. The temperature and pressure relief valve and the expansion relief valve are opened briefly. Water must run freely through the tundish and discharge pipe, and each valve must reseat cleanly.
- Strainer cleaned. Megaflo cylinders have a strainer that collects debris, housed in the pressure reducing valve cartridge. It is removed and flushed.
- Cartridges and valve seat cleaned. The pressure reducing cartridge, the expansion valve cartridge and the seat are cleaned according to local water quality.
- Immersion heater checked. In hard water areas it is descaled, and the inner vessel can be inspected through the immersion heater boss.
- Expansion provision checked. A Megaflo uses an internal air gap instead of an external vessel. Where a separate expansion vessel is fitted, its pre-charge pressure is checked at the Schrader valve and topped up if needed.
- Tundish and discharge pipe checked. The tundish should be vertical, no more than 600 mm from the connection to the temperature and pressure relief valve, sited so any discharge is visible, and the route out must be clear.
An unvented cylinder holds water at mains pressure. The temperature and pressure relief valve, the expansion relief valve and the tundish are safety devices, not adjustable settings. Opening them, recharging an air gap or changing a cartridge is work for an engineer qualified on unvented hot water systems.
Who may service an unvented cylinder, and how do you check?
Servicing an unvented cylinder is work for a competent person, and manufacturers put that in writing. Heatrae Sadia states that service work must be carried out by a competent person, in line with the maintenance section of the installation instructions. In England and Wales the same manufacturer advises customers to check that the installer holds the G3 qualification for unvented systems. G3 is the qualification for unvented hot water storage, and holders carry a registration card.
Baxi names a G3 qualified installer for follow-up work where a Megaflo tundish keeps dripping. Ask to see the registration card before any work starts, and ask which scheme the engineer is registered with.
Gas competence and unvented competence are separate things. An engineer may hold one and not the other, so ask specifically about the cylinder when you book. Our guide on what a boiler service includes shows how different the boiler visit is.
What should you watch for between unvented cylinder services?
Water at the tundish is the sign to act on. Drips or a trickle suggest a relief valve is passing, or that the internal air gap in a Megaflo has been lost. Baxi says persistent dripping means calling a G3 qualified installer. Hot water flow that has weakened over months can point to debris in the strainer and pressure reducing cartridge, which the annual service cleans.
Safe checks for a householder are limited to four things: the boiler pressure gauge, the thermostat and programmer settings, the reset button and bleeding radiators. Leave the cylinder valves, the tundish and the immersion heater alone.
If you are still on a vented system with a tank in the loft, our guide on converting a vented system to an unvented cylinder explains what the change involves.
How hot should an unvented cylinder store water?
HSE guidance is to store hot water at a minimum of 60 °C, and for it to reach 50 °C at the outlets within one minute. Cold water should stay below 20 °C where that is possible. Legionella bacteria multiply between 20 °C and 45 °C, and stagnant water helps them. HSE describes temperature control as the most reliable method, and says sampling in domestic premises is not usually needed.
In England, landlords have legal duties for the health and safety of their tenants. HSE names the 60 °C storage temperature at the cylinder as one of the controls. Storage volume plays into this as well, and our guide on what size hot water cylinder you need covers sizing for a household.
If a new or replacement unvented cylinder is on the cards, the Megaflo and unvented systems page explains the free home survey and the written fixed price that come before any work starts.
Sources
- Schedule 1 to the Building Regulations 2010 (Part G3, England)
- GOV.UK — Sanitation, hot water safety and water efficiency: Approved Document G
- GOV.UK — Building regulations approval: use a competent person scheme
- Heatrae Sadia — Get servicing savvy about cylinders
- Heatrae Sadia — Importance of servicing your cylinder
- Heatrae Sadia — 3 key things to consider when servicing a hot water cylinder
- Heatrae Sadia — Product warranty
- Glow-worm — Hydracyl unvented hot water cylinders instructions
- Baxi — How to recharge the air gap on a Megaflo unvented cylinder
- Vaillant — uniSTOR installation and maintenance instructions
- HSE — Hot and cold water systems: temperature control
- HSE — Legionella and landlords' responsibilities