Mains-pressure hot water to every tap in the house, installed, discharge-piped and safety-tested by a G3-qualified engineer, with the paperwork Building Control actually wants to see.
G3 qualified · Fixed-price quote · 267+ five-star reviews
Design, install, service and repair of unvented (mains-pressure) hot water cylinders. Full G3-compliant install including expansion vessel, PRV, tundish, discharge pipework to safe location, and annual servicing of the safety devices.
Family homes running multiple showers or bathrooms; system-to-combi replacement isn't always the right call, an unvented cylinder often gives better flow to multiple outlets. Larger properties, self-builds, extensions with second bathrooms.
When you're losing hot water flow while a second tap is running; when replacing an old vented cylinder and loft tank; when converting a loft (freeing up the tank space); when installing a second bathroom.
Unvented cylinders store hot water at mains pressure and include safety devices that MUST be installed and maintained correctly. G3 is the legal qualification for anyone working on them, installs by non-G3 engineers are unsafe and unnotifiable to Building Control.
The mistakes that turn small jobs into big bills, and how a qualified engineer keeps them from happening.
Unvented cylinders can, in extreme fault conditions, become a pressure vessel with the energy of an explosion. G3 exists for a reason, an unqualified install skips the safety chain that prevents this.
A cylinder without correctly sized, correctly routed discharge pipework can't safely vent in a fault condition. Common on cheap installs; unacceptable to Building Control.
Expansion vessels lose pre-charge, PRVs seize, tundishes drip unnoticed. All catchable in a yearly service; all catastrophic if ignored for years.
Undersized cylinders run out of hot water mid-shower; oversized ones cost a fortune to reheat. Sizing to actual demand matters.
We check mains pressure and flow, number of bathrooms, expected simultaneous demand, and location for the cylinder and discharge pipework.
Cylinder, expansion vessel, PRV, tundish, discharge pipe, controls and Building Regulations notification, all included, priced in writing.
Cylinder, safety group and discharge pipework installed to G3 spec, all pipework insulated, controls wired and configured.
Pressure tested, safety devices verified, working pressures recorded, cylinder brought up to temperature.
Building Regulations notification and manufacturer warranty registered. 2-year workmanship guarantee on the install.
Every shower, tap and bath runs at full flow, no more losing pressure when someone flushes the loo.
Frees up loft space (useful for loft conversions) and removes the risk of a tank leak from above.
Two showers running at once without dropping to a dribble.
Modern unvented cylinders are typically stainless steel with 25+ year design life.
G3-qualified install, discharge to safe location, Building Regulations notified.
Accredited & trusted by the brands we install
Materials, methods and variations, the specifics that separate a proper install from a rushed one.
G3 is the qualification for unvented hot water systems, it's part of the Building Regulations. Anyone installing, servicing or repairing an unvented cylinder must hold G3. Non-G3 work is not lawful and cannot be notified to Building Control. Calvin is G3 qualified.
Every unvented cylinder needs: an expansion vessel (accommodating heated water expansion), a pressure relief valve (releasing water if pressure exceeds design), a temperature/pressure relief valve (belt-and-braces if the PRV fails or a thermostat fails), a tundish (visible air-break so you can see if the PRV is discharging), and correctly-sized discharge pipework routing safely to outside or a tundish drain.
150L is entry-level for a small family; 210L is common for a 2-bathroom home; 300L+ for larger properties or high-demand households. Sizing is about simultaneous demand plus reheat time, undersizing is the more common mistake.
The G3 rules on discharge pipework are specific, pipe diameter, maximum length, number of bends, and safe termination point are all defined. A properly designed install routes discharge to a visible outside termination or an approved internal tundish arrangement. Getting this wrong is the number-one failure point of non-specialist installs.
Expansion vessel pre-charge tested and re-pressurised, PRV manually operated to verify it seats correctly, T&P valve verified, tundish checked for signs of leakage, cylinder thermostat tested, working pressures recorded. All logged on a service sheet.
G3 is the qualification required under Building Regulations for anyone installing, servicing or repairing an unvented hot water cylinder. Non-G3 work is not lawful; Calvin holds G3.
Depends on cylinder size, location, existing pipework and discharge routing. We survey and give a fixed written quote, no per-day surprises.
Annually, the expansion vessel loses pre-charge over time and the safety devices need verification. It's also usually a warranty condition.
Yes, that's the whole point of unvented. The cylinder stores hot water at mains pressure so every outlet gets full flow, even with multiple taps running.
No, unvented systems remove the need for a loft tank. This is one of the main reasons people convert during a loft conversion.
150L for a small home, 210L for typical 2-bathroom family homes, 300L+ for larger properties. We size it against your actual simultaneous demand at the survey.
Yes, every G3-compliant install is notified under Building Regulations. You receive the compliance certificate afterwards.
2 years on workmanship, plus manufacturer warranties on the cylinder and controls.
A selection of real installs across Ashford, Surrey and West London, no stock photography.
Speak directly to Calvin, 24 years on the tools, no sales scripts, honest advice.
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