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Replace your hot water cylinder.
G3 certified install
Vented or unvented — sized properly, installed safely, with the right grade of insulation.
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Hiring a central heating, without the regret.
Four moves that separate a smooth job from a nightmare.
Wrong size for household
180L too small for family of 4+. 250L minimum for 4-bed home.
Pressure relief discharge
Persistent dribble from outside pipe = faulty expansion vessel or pressure relief valve. Get checked.
Skipped annual G3 service
Without service, cylinder warranty voids. Insurance may reject claims from cylinder failure.
Limescale build-up
Hard water areas need annual descale or water softener. Cheap cylinders fail in 8–12 years in hard water; quality cylinders 20+ years.
Costs & timeline
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Indicative UK ranges and what affects price.
Cost range
By job type
Inc. VAT · 2026
Source: NMT quotes
Source: NMT quotes
Unvented 180L cylinder (Megaflo)Most common UK
£700–£1.2k
Unvented 250L cylinderLarger households
£900–£1.5k
Vented copper cylinderTraditional, gravity-fed
£250–£500
Heat pump cylinder (large coil)Sized for low temp
£1.4k–£2.5k
Install labourG3 qualified for unvented
£400–£900
Annual G3 serviceMandatory unvented service
£80–£150
!
Quote spread is typically ± 18% — always get 3 quotes.
At a glance
InfographicThe Central Heating briefing.
Infographic
Central Heating quick-view
Hot water cylinders store domestic hot water for system boilers and heat pumps. Expect to pay £800–£2,500 for a UK hot water cylinder replacement depending on type, capacity, and complexity.
What Does the Work Involve?
G3 unvented hot water qualified plumber required for unvented cylinders. Old cylinder drained and removed (often in airing cupboard or utility room). New cylinder positioned. Boiler primary circuit connected. Mains cold supply connected. Hot outlet to taps connected. Pressure relief, expansion vessel, immersion heater all installed. System filled, tested, commissioned.
Typical Costs
| Item | Low (£) | High (£) | Notes |
|---|---|---|---|
| Unvented 180L cylinder (Megaflo) | 700 | 1,200 | Most common UK |
| Unvented 250L cylinder | 900 | 1,500 | Larger households |
| Vented copper cylinder | 250 | 500 | Traditional, gravity-fed |
| Heat pump cylinder (large coil) | 1,400 | 2,500 | Sized for low temp |
| Install labour | 400 | 900 | G3 qualified for unvented |
| Annual G3 service | 80 | 150 | Mandatory unvented service |
| Whole cylinder replace fitted | 1,200 | 2,500 | 180–250L unvented |
How Long Does It Take?
Like-for-like cylinder swap: 1 day. Vented to unvented conversion: 1–2 days. Storage cylinder installation new: 1–2 days.
DIY or Professional?
Unvented cylinder: G3 qualified plumber only. Vented (gravity-fed): general plumber can install.
Choosing the Right Tradesperson
G3 unvented hot water qualified plumber. Brand: Megaflo (Heatrae Sadia) — market leader. Telford, Range, Andrews are alternatives. Stainless steel cylinder longer life than enamelled steel.
UK Regulations
Building Regs Part G3 — unvented hot water requires qualified installer and certificate. Annual mandatory G3 service to maintain insurance and warranty. Cylinder energy rating now applies (A-G scale).
Common Problems
- Wrong size for household: 180L too small for family of 4+. 250L minimum for 4-bed home.
- Pressure relief discharge: Persistent dribble from outside pipe = faulty expansion vessel or pressure relief valve. Get checked.
- Skipped annual G3 service: Without service, cylinder warranty voids. Insurance may reject claims from cylinder failure.
- Limescale build-up: Hard water areas need annual descale or water softener. Cheap cylinders fail in 8–12 years in hard water; quality cylinders 20+ years.
Frequently Asked Questions
Unvented or vented?
Unvented (Megaflo): mains-pressure hot water, no loft tank, modern standard. Vented: traditional, requires loft cold-water tank, lower pressure. Unvented is the modern UK choice.
What size cylinder?
1 bathroom: 120–180L. 2 bathrooms: 180–250L. 3+ bathrooms: 250–300L. Heat pump systems usually need 250L+ to compensate for slower heating.
Stainless steel or copper cylinder?
Stainless steel: lighter, longer life, more expensive. Copper: cheaper, heavier, susceptible to limescale. Modern installations are mostly stainless.
How long does a cylinder last?
Stainless: 20–30 years. Copper: 15–25. Cheap brands: 10–15.
Should I switch to a combi (no cylinder)?
If household uses less than 1 bathroom simultaneously, yes — combi saves space. If 2+ bathrooms in simultaneous use, keep cylinder.
Megaflo vs Telford vs Range?
Megaflo: market leader, premium price. Telford: equivalent quality, slightly cheaper. Range: budget option, equivalent for domestic use.
This guide was written with AI assistance and is intended for general information only. Prices are estimates based on UK averages and may vary by region. Always get at least three quotes and consult a qualified professional before starting any work.
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