Unvented CylinderInstallation
Mains-pressure hot water, supplied and fitted from £1,640 + VAT (£1,968 inc VAT). Guide price in 30 seconds, fixed price after a free survey.
Cylinder job facts
How much does an unvented cylinder cost?
Supplied and fitted, cylinder and labour together, ex VAT. These are the figures the fixed price starts from — confirmed in writing after a free survey.
| Cylinder | Suits | Replacement1 day | Vented conversion2 days |
|---|---|---|---|
| 150 L | 1 bathroom, 1 to 2 people | £1,640£1,968 inc VAT | £2,390£2,868 inc VAT |
| 180 L | 1 bathroom, 2 to 3 people | £1,720£2,064 inc VAT | £2,470£2,964 inc VAT |
| 210 L | 1 to 2 bathrooms, 3 to 4 people | £1,850£2,220 inc VAT | £2,600£3,120 inc VAT |
| 250 L | 2 bathrooms, 4 to 5 people | £2,000£2,400 inc VAT | £2,750£3,300 inc VAT |
| 300 L | 2 to 3 bathrooms, 5 or more people | £2,150£2,580 inc VAT | £2,900£3,480 inc VAT |
Prices ex VAT unless stated. 150 L unvented cylinder supplied and fitted in Great Bedwyn, Sep 2025: £1,981 inc VAT all in.
What affects the price
Two homes with the same cylinder can be several hundred pounds apart. This is where the difference usually comes from, and every one of these is settled on the survey before you get a price.
- Size of cylinder. Between a 150 L and a 300 L the unit alone is £510 apart. Oversizing costs money to buy and money to heat.
- Replacement or conversion. Swapping a failed unvented cylinder is 1 day. Coming off a vented system means a new mains-pressure supply and discharge pipework — 2 days, and £750 more in labour.
- Your incoming mains. An unvented cylinder is only as good as the water feeding it. If the mains flow is poor, the pipework to the cylinder may need upgrading. We measure the flow rate on the survey rather than guessing.
- Where the cylinder lives. An airing cupboard with room to work is straightforward. A loft, a boarded-in cupboard or a first-floor position that needs a longer discharge run to outside all add time.
- Taking the old tank out. Coming off a vented system usually leaves a cold tank in the loft. Removing it is optional and priced separately.
- Electrical work. A new immersion supply is notifiable electrical work. Will is not Part P registered, so our electrician does it, issues the certificate and notifies building control. The two visits are booked together.
What will my cylinder cost?
Four quick choices and you have a guide price built from the figures we actually charge. No email address needed.
Your guide price
£1,702 to £1,998 + VAT
£2,042 to £2,398 inc VAT
Usually 1 day on site. Hot water is off for most of that day.
What that covers
- 210 L unvented cylinder, fittings and sundries£1,150
- Labour: replace an existing unvented cylinder (1 day)£700
- • G3-qualified installer, Building Regulations notification included
- • Old cylinder removed and disposed of
- • Tested, commissioned and shown to you before we leave
- • 12-month guarantee on workmanship, manufacturer warranty on the cylinder
150 L unvented cylinder supplied and fitted in Great Bedwyn, Sep 2025: £1,981 inc VAT all in.
This is a guide, not a quote. We survey for free and give you one written fixed price before any work starts.
Book a free survey for this priceOr call 01264 502027Three ways we do cylinders
Like-for-like unvented replacement
From £1,640 + VAT
£1,968 inc VAT
Your existing unvented cylinder has failed or is past its best. Same position, one day, hot water back by evening.
Book a free surveyVented to unvented conversion
From £2,600 + VAT
£3,120 inc VAT
Lose the loft tank and get mains-pressure hot water to every tap and shower. Two days on site.
Book a free surveyCylinder for a heat pump
Priced on survey
Larger coil, sized for lower flow temperatures. Priced on survey with your heat pump installer.
Heat pump cylindersSigns your cylinder is on its way out
- Hot water runs out faster than it used to, or takes longer to reheat
- Water dripping from the discharge pipe outside, or the tundish, more than a few drops
- Rusty or discoloured hot water, or a metallic smell
- Banging or gurgling from the cylinder cupboard
- It is more than 15 years old and has never had the expansion vessel or valves serviced
- Damp patch or corrosion around the base of the cylinder
Vented or unvented?
| Vented (tank in loft) | Unvented (mains pressure) | |
|---|---|---|
| Shower pressure | Depends on loft height, often weak | Strong, same at every tap |
| Loft tank | Needed | Gone |
| Needs a pump for showers | Usually | No |
| Installer | Any plumber | G3 qualified, notified to Building Control |
| Depends on mains flow | No | Yes, we test it first |
| Annual check | Not usually | Recommended (valves and expansion vessel) |
Unvented cylinders by Will Gaze
Cylinders are the job I enjoy most: a day's careful work that transforms how a house feels every morning. 22 years in the trade, G3 qualified for unvented hot water, G1 trained for heat pump cylinders, WaterSafe approved. I do the survey, I do the fitting, and I hand it over to you working.
- G3 unvented hot water qualification, Building Regulations notification included
- WaterSafe (WRAS) approved plumber
- Mains flow and pressure tested before we recommend a cylinder
- Old cylinder removed and disposed of, cupboard left clean
- We do not work on gas or oil boilers and will say so if that is what you need
Cylinder installationacross Andover, Marlborough & Hungerford
Andover (SP10, SP11), Marlborough (SN8), Hungerford (RG17), Pewsey (SN9), Tidworth (SP9), Stockbridge (SO20) and the villages between, from our base near Marlborough.
G3 and building regs, explained
An unvented cylinder is the one piece of plumbing in a house that is stored under mains pressure. That is why the law is specific about who may fit it.
Why the qualification exists
An unvented cylinder holds hot water under mains pressure with no vent to the air. If the controls fail and nothing releases the pressure, the cylinder itself becomes the release. The safety devices — expansion vessel, pressure relief, thermal cut-out and the discharge pipe that carries hot water safely outside — are what stop that, and they have to be fitted and set correctly.
What the law actually requires
Installing an unvented hot water system is controlled work under Building Regulations Part G3 in England and Wales. The installer must hold the G3 unvented hot water qualification, and the work must be notified to building control. It is not paperwork you can skip: an unnotified cylinder can hold up a house sale and can give an insurer a reason to decline a claim.
What Will holds
Will is G3 qualified for unvented hot water and WaterSafe (WRAS) approved, with 22+ years on the tools. He notifies the work as a competent person, so you are not applying to building control yourself, and the notification is included in the price rather than added at the end.
What Will does not do
Rosebourne is not Gas Safe, OFTEC or MCS registered and does no work on gas or oil boilers. If your cylinder is heated by a boiler that also needs attention, Will does the cylinder and recommends a Gas Safe engineer for the boiler. The electrical side of an immersion supply is done by a qualified electrician, who issues the certificate.
Read before you decide
The true cost of upgrading to an unvented cylinder
What changes in the house, what it costs, and the questions to ask before you commit.
Read the guide →Hot water cylinder guide
Vented, unvented, direct, indirect: which is which and which suits your home.
Read the guide →Cylinder replacement cost guide 2026
Where the money goes in a cylinder swap and how to keep the bill sensible.
Read the guide →Cylinder questions, answered straight
How much does an unvented cylinder cost supplied and fitted?
A like-for-like 150 L replacement starts from £1,640 + VAT (£1,968 inc VAT), cylinder, fittings, labour and disposal included. Larger cylinders and conversions from a vented system cost more; the calculator on this page gives you a guide price in 30 seconds. A real example: a 150 L cylinder supplied and fitted in Great Bedwyn in September 2025 came to £1,981 inc VAT all in.
Do I legally need a G3 plumber for an unvented cylinder?
Yes. Unvented cylinders store hot water under mains pressure, so Building Regulations require the installer to hold the G3 unvented hot water qualification and to notify the work. Will is G3 qualified and WaterSafe (WRAS) approved, and the notification is included in our price.
How long will I be without hot water?
Most of the day for a like-for-like swap; the new cylinder is usually heating by late afternoon. A conversion from a vented system takes two days, with hot water restored at the end of the second day. We tell you the plan before we start.
What size cylinder do I need?
Roughly 35 to 45 litres per person, rounded up for a second bathroom or a big bath. 150 L suits a one-bathroom home for two people, 210 L covers most family homes, 250 to 300 L for two or three bathrooms. We confirm the size and check your mains flow rate on the survey, because an unvented cylinder is only as good as the water pressure feeding it.
Is it worth converting from a vented tank system?
If you have weak showers, a tank in the loft you would rather be rid of, or you are planning a bathroom refit, usually yes. You get mains-pressure hot water everywhere, free up the loft, and the cylinder heats faster. It only works if your incoming mains can supply enough flow, which is the first thing we test.
What is included and what is not?
Included: the cylinder, expansion vessel, safety valves and fittings, discharge pipework, labour, removal and disposal of the old cylinder, Building Regulations notification, testing and a handover. Not included: electrical work for a new immersion supply (our electrician prices this with a certificate), decoration, and any boiler work (we do not work on gas or oil boilers and will recommend a Gas Safe engineer if yours needs attention).
Can you replace an immersion heater?
Yes, and it is often the cheapest way to get hot water back. If the element has failed but the cylinder itself is sound, replacing the element and thermostat is a fraction of the cost of a new cylinder, and we will tell you plainly which one you are looking at before you commit. A titanium element is worth the small extra in hard water, which is most of this area.
Who does the electrical side of an immersion heater?
A qualified electrician. Will is not Part P registered, so the electrical work is done by the electrician we work with, to BS 7671 — they issue the certificate and notify building control where Part P requires it. Will does the cylinder and the plumbing under his G3 qualification, and the two visits are booked together so you are not chasing anyone.
What is the difference between a single and a dual element cylinder?
A single element heats the whole cylinder. A dual element has a short top element for a quick tankful and a longer bottom one for a full heat, which suits an Economy 7 tariff: the bottom element runs on the cheap overnight rate, the top one gives you a boost during the day without paying to heat the lot.
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Ready for proper hot water pressure?
Use the calculator for a guide price, then book a free survey. You get one written fixed price and a date, and we stick to both.