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01 · Ask
Repair, replace or upgrade?
Cold rads, no hot water, F22 fault code? Describe what's happening — the AI tells you if it's a £150 repair or a £3k replacement.
Install a heat-only boiler.
Conventional / regular boiler with header tank — for traditional vented systems with high hot-water demand.
✓ Updated May 2026✓ Free quotes✓ Vetted pros
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Hire a boiler engineer. Without the warranty void.
Read the brief on sizing, brands and warranty rules — then let Three local engineers quote on the right boiler for your house.
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02 · Read the brief
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kW sizing, modulation ratios, Benchmark cert, manufacturer warranty terms. Know what to ask before they recommend the most expensive box on the van.
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03 · Compare
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Three local engineers come back with itemised quotes — boiler, flue, controls, power-flush, commissioning — so the like-for-like vs upgrade choice is yours.
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Top tips
Hiring a boiler engineer, without the regret.
Four moves that separate a smooth job from a nightmare.
Get a Gas Safe ID before letting them in.
Boilers are gas appliances. Anyone working on yours must be Gas Safe registered — and on the right scheme for your fuel (LPG, oil, natural gas are separate).
Demand the Benchmark certificate.
Every new boiler comes with a Benchmark commissioning checklist. Without it, the manufacturer warranty is void — and the certificate goes in your seller's pack later.
Size the boiler to the radiators, not the house.
Oversized combis short-cycle, wear out fast and cost more to run. A heat-loss calc — not a 'same as before' swap — is the sign of a careful installer.
Power-flush before fitting.
On a 10-year-old system, sludge will write off your new boiler's heat exchanger in 18 months. A power-flush should be quoted; if it's not, ask why.
Costs & timeline
Know what it costs. Know when it ends.
Indicative UK ranges and what affects price.
Cost range
By job type
Inc. VAT · 2026
Source: NMT quotes
Source: NMT quotes
Boiler service (annual)
£80–£150
Combi boiler swap (like-for-like)
£1.8k–£3k
Combi boiler upgrade (premium)Vaillant/Viessmann tier
£2.8k–£4.5k
System boiler + cylinder
£3k–£5.5k
Power flush
£450–£900
Conversion from back-boilerInc. removal + replumb
£3.5k–£6k
!
Quote spread is typically ± 18% — always get 3 quotes.
At a glance
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Boiler Engineer explained
Heat-only (or "conventional" or "regular") boilers work with a hot water cylinder AND a cold water storage tank in the loft. They were the UK standard for decades and remain in many older homes. New installs are less common today but they suit specific situations — particularly older houses with intact gravity-fed systems. This guide covers conventional boiler install costs in 2026 and when they suit better than combi or system.
Most heat-only installs today are like-for-like replacements rather than new builds.
What Does the Work Involve?
- Boiler installation with flue, condensate drain.
- Hot water cylinder (if not retaining existing).
- Cold water storage tank in loft (if not retaining).
- Programmer and motorised valves.
- System commissioning.
Typical Costs
| Configuration | Low £ | High £ | Notes |
|---|---|---|---|
| Like-for-like heat-only swap | 2,000 | 3,200 | Reusing cylinder & tank |
| Full conventional system rebuild | 3,500 | 5,500 | Inc. tank + cylinder |
| System → conventional conversion | +500 | +1,500 | Reinstating loft tank |
When Heat-Only Suits
- Existing system in good condition, particularly cylinder.
- Old radiator network needs gravity feed (rare).
- Mains pressure low (combi/system suffer).
- Houses with vulnerable mains supply.
UK Regulations
- Gas Safe + Building Regs as standard.
- Loft tank must meet contamination prevention (Byelaw 30 / Water Regs).
Common Problems
- Old loft tank failing — leaks into rooms below.
- Heat loss from uninsulated cylinder — annual cost adds up.
- Slow hot water recovery — cylinder reheating slowly.
Frequently Asked Questions
Should I replace heat-only with combi?
Usually yes for smaller homes. Heat-only is becoming uncommon in new installs.
How long do heat-only boilers last?
15–25 years. Cylinder typically 20+ years.
Is heat-only more efficient?
Modern heat-only boilers are similarly efficient to combis. Heat loss from cylinder is the main inefficiency.
Will heat-only handle higher flow than combi?
Yes — cylinder stores hot water for multiple-tap use.
Are heat-only boilers still made?
Yes — major brands still produce them, primarily for replacement market.
What about the loft tank?
If replacing, plastic/polyethylene tank required by Water Regs. Insulated and sealed for contamination prevention.
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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