Unvented hot water cylinders deliver mains-pressure hot water throughout your home without the need for a cold water tank in the loft. They are found in thousands of homes across Kent, particularly in larger properties and those that have been renovated or modernised. But unlike a standard vented cylinder, unvented systems operate at high pressure and require specialist knowledge to service and repair safely.
Under Part G3 of the UK Building Regulations, only engineers holding a G3 qualification can legally work on unvented hot water cylinders. At Ability Plumbing & Heating, our engineers hold this qualification and have extensive experience servicing, repairing, and installing unvented cylinders from all major manufacturers including Megaflo, Gledhill, Heatrae Sadia, and Worcester Bosch.
Call 01732 904098 to book your unvented cylinder service.
What Is an Unvented Hot Water Cylinder?
An unvented cylinder connects directly to the mains water supply rather than being fed by a cold water storage tank in your loft. This means the hot water throughout your home is delivered at mains pressure, giving you powerful showers and fast-filling baths without a pump.
Because unvented cylinders store hot water at mains pressure, they incorporate multiple safety devices to manage temperature and pressure. These devices must be tested regularly to ensure they function correctly. This is why annual servicing is essential and why you need a G3-qualified engineer.
What Does an Unvented Cylinder Service Include?
Our annual unvented cylinder service is a systematic check of every safety device and component. Here is what we inspect and test:
- Temperature and pressure relief valve (T&P valve) -- This is the primary safety device. It opens to release water if the temperature or pressure exceeds safe limits. We manually test it to confirm it operates and reseats properly.
- Expansion vessel -- The expansion vessel absorbs the natural expansion of water as it heats. We check the pre-charge pressure (typically 2.5-3 bar) and re-pressurise it if necessary.
- Tundish and discharge pipework -- The tundish provides a visible air gap in the discharge pipe from the T&P valve. We check it is clear, correctly positioned, and that the discharge pipe routes safely to a drain or external point.
- Immersion thermostat -- We check the operating thermostat is set correctly (typically 60-65 degrees Celsius) and functioning properly.
- High-limit thermostat (energy cut-out) -- This safety device cuts power to the immersion heater if the temperature exceeds a safe limit (typically 85-90 degrees Celsius). We test it to confirm it trips correctly.
- Pressure-reducing valve -- If fitted, we check it is maintaining the correct inlet pressure.
- Check valve (non-return valve) -- We verify it prevents heated water from flowing back into the cold mains supply.
- Anode rod inspection (where accessible) -- Some cylinders have sacrificial anodes that protect against internal corrosion. We check condition and advise on replacement if needed.
- Visual inspection -- We look for leaks, corrosion, damage, and any signs of wear on pipework and fittings.
Signs Your Unvented Cylinder Needs Attention
Contact us if you notice any of the following:
- Water dripping from the tundish or discharge pipe -- This usually means the T&P valve is releasing water, which could indicate the expansion vessel needs re-pressurising or a valve needs replacing.
- Water coming from the pipe on the outside wall -- This is the end of the discharge pipe and means the T&P valve has activated. If it happens frequently, the cylinder needs servicing.
- Reduced hot water pressure -- A drop in pressure may indicate a problem with the pressure-reducing valve or a blockage.
- Hot water not reaching set temperature -- The thermostat may need recalibrating or replacing.
- Unusual noises from the cylinder -- Banging, clicking, or rumbling sounds can indicate limescale buildup on the immersion element or a fault with a safety valve.
- Leaks around the cylinder -- Any visible leak should be investigated promptly.
Why Annual Servicing Matters
- Manufacturer warranty -- Most unvented cylinder manufacturers, including Megaflo (Heatrae Sadia) and Gledhill, require annual servicing by a G3-qualified engineer as a condition of their warranty. Megaflo cylinders come with a 25-year warranty, but only if they are serviced annually. Skip a service and you could void decades of warranty cover.
- Safety -- The safety devices on an unvented cylinder are your protection against overheating and over-pressurisation. Testing them annually confirms they will work when needed.
- Legal compliance for landlords -- While there is no specific legal requirement for homeowners, landlords have a duty to ensure all safety devices are maintained and functioning. Annual servicing demonstrates compliance.
- Insurance -- Some home insurance policies require proof of regular maintenance for pressurised hot water systems. Check your policy.
- Prevention -- A small issue found during a service (such as a slowly failing expansion vessel) costs far less to fix than the water damage from a T&P valve that discharges continuously because the expansion vessel has failed.
Unvented Cylinder Brands We Service
Our G3-qualified engineers service and repair unvented cylinders from all major manufacturers:
- Megaflo (Heatrae Sadia) -- The most widely installed unvented cylinder in the UK
- Gledhill -- Including the Stainless Lite and PulsaCoil range
- Heatrae Sadia -- Including Megaflo Eco and other models
- Worcester Bosch -- Greenstore unvented cylinders
- Telford -- Tempest range
- Range Tribune -- All models
- Joule -- Invacyl range
- OSO -- Including the HoTT range
Unvented Cylinder Service Cost
Annual unvented cylinder servicing with Ability Plumbing & Heating starts from around £120.
Typical pricing:
- Annual service (inspection, testing, and report): £80-£200
- Expansion vessel re-pressurisation (during service): Included or nominal extra charge
- T&P valve replacement: £150-£300 (parts and labour)
- Expansion vessel replacement: £200-£400
- Full cylinder replacement: £1,000-£2,500 (depending on size and model)