Unvented Hot Water Systems

Unvented Hot Water CylinderInstallation & ServicingAcross Bedfordshire.

Mains-pressure hot water, properly installed and G3 certified — Megaflo, Gledhill, Telford and every major brand. Annual safety checks, repairs and full system upgrades from a Gas Safe engineer.

Request a Quote 07815 022377

G3 Qualified

unvented installer

10+ Years

experience

Fixed-Price

written quotes

Fully Insured

public liability

Gledhill Stainless ES unvented hot water cylinder installation with full copper pipework, expansion vessel and isolation valves — G3 certified install by On-Tap Plumbing & Heating in Bedfordshire

Service Overview

What's covered, who it's for, when to call.

What it is

An unvented hot water system stores hot water in a sealed, pressurised stainless-steel cylinder fed directly from the mains. With no cold-water tank in the loft and no gravity-fed pressure drop, you get high-flow hot water at every tap and shower at the same pressure as your incoming mains. Because the cylinder is sealed and pressurised, installation, servicing and any future work is legally restricted to engineers holding a current G3 unvented hot water qualification — which we hold and renew.

Who it's for

Homeowners replacing a tired open-vented (gravity-fed) system and tired of weak showers. Households with two or more bathrooms where flow rate matters more than peak heat output. Landlords upgrading older properties to bring shower performance in line with modern tenant expectations. Anyone planning a loft conversion who needs to remove the cold-water tank to free up the space.

When it's needed

Now, if you're already noticing the warning signs: lukewarm showers when someone else turns on a tap, weeping pressure-relief discharge pipework, sediment in hot taps, or a cylinder that's gone visibly tired around the temperature and pressure relief valve. Unvented cylinders have a serviceable lifespan of 15-25 years; the annual G3 safety check is what spots failing expansion vessels and seized PRVs before they let go.

Why a professional matters

Unvented systems are pressurised vessels that can — if installed or maintained incorrectly — fail with serious consequences. Building Regulations Part G requires G3-certified competence for any work on an unvented cylinder above 15 litres, and home insurers will refuse claims on systems worked on by unqualified installers. Beyond the regs, a properly specified and balanced unvented system genuinely transforms how a house feels to live in.

The Cost of Waiting

Most unvented cylinder failures are predictable — and preventable.

Almost every unvented cylinder we replace failed for one of the same handful of reasons. Booked-in annual G3 servicing catches every one of these before they turn into a leak through the ceiling:

Expansion vessels fail silently after 5-7 years — the cylinder then dumps hot water out of the tundish every time it heats, wasting energy and triggering the pressure-relief valve.
Limescale builds up on the immersion heater and internal coil, slowing recovery time and dropping the usable hot-water draw-off by 20-30%.
Temperature and pressure relief valves seize through lack of operation — the very valves designed to stop a catastrophic cylinder rupture.
Inlet group strainers clog with mains debris, throttling cold feed and creating uneven, juddering hot-water pressure at the taps.

Our Process

Five steps. No surprises.

Survey & specification

We measure your incoming mains flow and pressure, count bathrooms and demand points, and spec a cylinder size and recovery rate matched to how your household actually uses hot water.

Fixed-price written quote

Itemised quote covering cylinder, controls, expansion vessel, isolation valves, tundish, discharge pipework and removal of the old system. No verbal estimates.

Installation to G3 standard

Old cylinder drained and removed, new cylinder installed with full primary and secondary pipework, expansion vessel correctly pre-charged, discharge pipework run in copper to Building Regs Part G.

Commissioning

System filled, pressure-tested, vessel charge verified, PRV and T&P valves manually tested, controls programmed, and a Benchmark commissioning certificate completed.

G3 certificate & handover

Building Regulations compliance certificate notified through our competent-person scheme, plus a walk-through covering controls, isolation and what to look for between annual services.

Why Choose On-Tap

The benefits, plainly stated.

Mains-pressure performance

Power-shower flow rates at every outlet, even with multiple draw-offs running at the same time. No loft tank, no gravity loss.

G3 certified

Every installation completed by a G3-qualified engineer and notified through a competent-person scheme — fully Building Regs compliant.

Clean, quiet, modern

No header tank in the loft, no overflow pipework, no tank insulation jacket. Frees up loft space and removes a known legionella risk.

Manufacturer warranties

Up to 25 years on the stainless cylinder body on premium brands, provided annual G3 servicing is maintained.

Fast recovery times

Properly sized cylinders reheat in 20-30 minutes — your household stops running out of hot water at the worst moment.

Honest sizing advice

We size cylinders to your real demand, not the biggest one we can sell. The right unit costs less to run and lasts longer.

In Depth

Unvented hot water systems — what you actually need to know.

Unvented cylinders are simple in principle but uncompromising in execution. Get the install right and the system runs reliably for two decades. Cut corners, and the warning signs appear within months. Here's the detail behind a proper installation.

Specification and sizing — why it matters

Sizing isn't guesswork. We calculate stored-hot-water demand against simultaneous draw-off — the number of taps, showers and baths that could be in use at the same time — and cross-reference against the incoming mains flow rate and pressure. An undersized cylinder leaves you cold mid-shower; an oversized one wastes energy reheating water you never use. Most three-bedroom homes land at 180-210 litres; four-bedroom homes with two bathrooms typically need 250-300 litres. We size to your actual use, not a generic table.

Brands we install and service

We install, service and repair every major unvented cylinder brand — Megaflo (Heatrae Sadia), Gledhill Stainless ES and BoilerMate, Telford Tempest, Range Tribune, OSO and Joule. Each has its own quirks in the expansion vessel arrangement, immersion access and inlet group layout — knowing them in detail is what makes diagnosis quick and second visits rare. Our G3 qualification covers the full range.

Annual G3 servicing — what's actually checked

A proper G3 service is not a five-minute visual. We isolate and discharge the cylinder, check and re-pressurise the expansion vessel (or replace it if it's failed), manually operate the temperature and pressure relief valves, descale the immersion if accessible, inspect the tundish for evidence of passing valves, check the discharge pipework run for compliance, and reset the controls. Every check is documented on a service record so you have evidence for insurance and warranty purposes.

Building Regulations Part G & compliance

Any unvented cylinder over 15 litres is notifiable work under Building Regulations Part G. As G3-qualified installers we notify every install through a competent-person scheme, meaning you receive a Building Regulations compliance certificate without involving Local Authority Building Control. The certificate is essential for house sale, remortgage and home insurance claims — and a system installed without notification will fail a homebuyer survey.

FAQs

Questions, answered.

Anything else? Call 07815 022377.

Do I really need a G3 qualified engineer?+

Yes. Any work on an unvented cylinder over 15 litres is legally restricted to G3-qualified engineers under Building Regulations Part G. Work carried out by unqualified installers is not just illegal — it voids home insurance and manufacturer warranties.

How much does an unvented cylinder installation cost?+

Most domestic installs land between £2,200 and £3,800 fully fitted, depending on cylinder size, brand, location of the cylinder and whether new discharge pipework needs to be run externally. Every quote is written, itemised and fixed before any work begins.

How often should it be serviced?+

Annually. The G3 service checks the expansion vessel charge, both safety valves, the immersion and the discharge pipework — the four most common failure points. Skipping it shortens the cylinder life and risks both warranty cover and insurance claims.

Will an unvented system improve my showers?+

Almost always, yes — provided your incoming mains can deliver enough flow. We test mains flow and pressure during the survey and tell you honestly whether an unvented upgrade will deliver the difference you're hoping for, or whether a different solution (such as a high-flow combi or accumulator) makes more sense.

What size cylinder do I need?+

It depends on bathrooms, household size and simultaneous demand. A typical three-bed home is well served by 180-210 litres; a four-bed with two bathrooms usually wants 250-300 litres. We size based on real demand, not a sales target.

Can I have an unvented cylinder with my existing boiler?+

Most modern system and conventional boilers will pair with an unvented cylinder. Combi boilers will not — they heat on demand and don't store water. If you're moving from a combi to a stored hot water system we'll spec the right boiler-and-cylinder combination together.

What's the warranty?+

Cylinder warranties range from 2 to 25 years depending on brand and model, with most premium stainless cylinders carrying 10-25 years on the cylinder body. Warranty cover is conditional on documented annual G3 servicing — another reason to keep yours up to date.

What areas do you cover?+

From our base in Westoning we cover Bedford, Milton Keynes, Luton, Hitchin, Flitwick, Biggleswade, Barton-le-Clay, Stevenage and the surrounding Bedfordshire and Hertfordshire region.

Related Services

Often booked alongside.

All services

Ready to get it sorted properly?

A fixed-price quote in writing, a Gas Safe engineer on site, and the job done right first time.