Methodology / Sources reviewed May 2026
Methodology + sources
How every cost range, grant detail, and regulatory statement on this site is sourced and calibrated. Below: the 19 primary sources, how often each is refreshed, what we take from each, and what is explicitly out of scope.
Primary sources
| Source | Refresh | What we take |
|---|---|---|
| Worcester Bosch UK worcester-bosch.co.uk | Annual + on launch | Greenstar 4000, 8000 Life, 8000 Lifestyle, Ri model range; published RRPs; Worcester Trade Accredited Installer warranty terms (up to 12 years) |
| Vaillant UK vaillant.co.uk | Annual + on launch | ecoTEC Plus, ecoFIT Pure model range; published RRPs; Advance Guarantee warranty terms (up to 10 years) |
| Ideal Heating idealheating.com | Annual + on launch | Logic Max, Vogue Max model range; published RRPs; warranty terms (up to 12 years via accredited installer) |
| Baxi baxi.co.uk | Annual + on launch | 800 Combi, 600 Combi, Megaflo System, 600 Heat range; published RRPs; Baxi Works warranty terms |
| Viessmann UK viessmann.co.uk | Annual + on launch | Vitodens 050-W, 100-W, 200-W range; published RRPs; Trained Installer warranty terms |
| Heatable heatable.co.uk | Monthly | Installer-direct price points, fixed-package pricing cross-check, regional install timing |
| BOXT boxt.co.uk | Monthly | Direct-purchase installed cost cross-check, 0% finance terms, brand availability |
| BoilerGuide boilerguide.co.uk | Quarterly | Industry editorial cross-reference; regional cost band benchmarking |
| Which? Best Buy Boilers which.co.uk | Annual | Brand reliability ratings, installer recommendation surveys, 2026 Best Buy list |
| Energy Saving Trust energysavingtrust.org.uk | Annual | Annual gas saving figures (GBP 200-GBP 580 G-to-A upgrade), sizing rule of thumb (kW per radiator), running cost calculations |
| Gas Safe Register gassaferegister.co.uk | Ongoing | Engineer registration verification, complaints process, ID card check protocol |
| gov.uk Boiler Upgrade Scheme gov.uk/apply-boiler-upgrade-scheme | On scheme update | BUS grant amounts (GBP 7,500 ASHP / GSHP, GBP 5,000 biomass), eligibility, MCS installer requirement, application flow |
| Ofgem ECO4 ofgem.gov.uk/environmental-and-social-schemes/energy-company-obligation-eco | On scheme update | ECO4 eligibility framework, qualifying benefits list, EPC band requirement, energy supplier obligation thresholds |
| DESNZ Heat and Buildings Strategy gov.uk/government/publications/heat-and-buildings-strategy | On policy update | Future Homes Standard 2025 detail, gas boiler new-build ban context, BUS funding commitments through 2028 |
| Boiler Plus 2018 (DBEIS guidance) gov.uk/government/publications/boiler-plus | On policy update | Smart thermostat / weather compensation / FGHR / weather compensation mandatory requirements for new combi installs in England |
| Building Regulations Part L + Part J planningportal.co.uk/buildingregulations | On Approved Document update | Condensing boiler mandatory requirement, flue distance rules, CO alarm requirement, Building Control notification routes via Competent Persons Scheme |
| MCS Certified Installer database mcscertified.com | Ongoing | Heat pump installer directory required for BUS grant claim, MCS certified equipment list |
| ONS energy expenditure ons.gov.uk | Annual | UK average household energy spend, gas vs electricity unit cost ratios for heat pump comparison |
| BBC Watchdog Live / consumer protection bbc.co.uk | Ongoing | Cold-call ECO4 scam pattern, consumer protection context for the "watch-outs" sections |
In scope
- UK domestic gas boiler replacement cost ranges (combi, system, regular, back-boiler conversion)
- OEM unit RRPs cross-checked against Heatable + BOXT installer-direct pricing
- UK 2026 typical installed cost ranges including labour + flue + filter + flush + Building Control
- Brand-specific warranty terms and accredited-installer routes
- kW sizing rules of thumb (Energy Saving Trust)
- Regional cost variation across UK regions
- ECO4 + BUS + Warm Home Discount grant frameworks and eligibility
- 0% finance, personal loan, boiler subscription, and credit card options
- Gas Safe + Building Regs Part L + Part J + Boiler Plus 2018 regulatory requirements
- Heat pump vs gas boiler cost + suitability comparison
- ErP A-G efficiency band framework and annual gas saving from upgrading
- UK domestic context only - not commercial or industrial boilers
Out of scope
- Specific installer / regional / property quotes - always get 2-3 quotes from Gas Safe registered engineers
- Diagnostic of specific boiler faults - call a Gas Safe engineer for individual diagnosis
- Commercial or industrial boiler pricing
- Off-grid LPG / oil boiler pricing beyond rural BUS / biomass context
- Detailed heat pump sizing and design (different professional discipline; see MCS certified installer directory)
- Country-specific pricing outside UK (US, Australian, EU pricing differs substantially)
- Substitution for an in-person inspection by a Gas Safe registered engineer
- Financial, legal, or engineering advice on specific installations
Calculation framework
Installed cost calibration
OEM unit RRP + UK average labour (GBP 500-GBP 1,500) + flue + magnetic filter + powerflush + Building Control. Cross-checked against Heatable and BOXT package pricing for the 80% common scenario (like-for-like combi swap, 1-day install).
Conversion premium
Additional GBP 500-GBP 2,000 over like-for-like for type changes (combi conversion, system conversion). Calibrated against back-boiler conversion benchmark line-items (decommission, pipework reroute, new flue, wall make-good).
Regional adjustment
Gas Safe engineer labour rate survey + installer density. London +15-25% vs UK national average; North East and Yorkshire -5 to -10%; Scotland / Wales / NI -5 to -10% with devolved grant variations.
Annual gas saving
Energy Saving Trust 2026 figures for upgrading from G-rated non-condensing to A-rated condensing combi: GBP 200-GBP 580 depending on house size. Cumulative figures use 12-year boiler life and flat gas pricing.
Grant amounts
From gov.uk + Ofgem published terms verbatim. BUS GBP 7,500 ASHP/GSHP, GBP 5,000 biomass. ECO4 covers full or near-full cost depending on supplier funding levels.
Repair costs
Gas Safe engineer call-out + part benchmarks from BoilerGuide, Heatable, and supplier published service rates. Range bands rather than point estimates because real costs vary by engineer and region.
Refresh cadence
Single source of truth: LAST_VERIFIED_DATE and LAST_VERIFIED_LABEL in src/lib/schema.ts. Rolling either forward updates every freshness indicator on the site automatically (footer stamp, hero badge, Article schema dateModified, About + Methodology page badges). Refresh triggers:
- Monthly: first-business-week pass of OEM RRPs + Heatable + BOXT pricing
- Quarterly: Energy Saving Trust running cost figures + ONS energy expenditure
- Annual: Which? Best Buy Boilers update + manufacturer warranty term review
- On policy update: ECO4 + BUS + Warm Home Discount + devolved grant changes
- On flagged correction: user-reported factual error escalated to next refresh cycle
Limitations
- Regional cost variation: London +15-25% can be wider in central postcodes; rural and island installs can be higher than urban regional averages
- Plan-year + RRP volatility: manufacturer RRPs can move 5-10% within a year on supply chain changes; check current pricing if planning install
- Heatable / BOXT scheme variability: installer-direct pricing varies with promotions and seasonal demand
- Grant eligibility complexity: ECO4 in particular has 8+ qualifying benefits with sub-criteria; this site simplifies for reference, but the energy supplier or ECO4 referral installer makes the final eligibility determination
- Brand availability: smaller brands (Glow-worm, Alpha, Potterton, Ferroli) are covered briefly but not depth - the 5 priority brands account for ~85% of UK domestic installs
Corrections process
Spot a factual error or price that has drifted? Email [email protected] with:
- The page URL where you saw the error
- The specific text that needs correcting
- The correct figure / detail with a citation
We acknowledge corrections within 5 business days and update inline within the next monthly refresh cycle. Out-of-cycle update for material consumer protection issues (e.g. wrong grant figure that would mislead applicants).
Do not email for boiler emergencies. Call 0800 111 999 if you smell gas. For installation or service questions, find a Gas Safe registered engineer at gassaferegister.co.uk.
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