Boiler Replacement Costs UK 2026: Real Installed Prices

A like-for-like combi swap in 2026 typically costs £1,800–£3,500 fully installed, with most homes landing around £2,200–£2,800. Boilers themselves are roughly £700–£1,800 for the unit; the rest is labour, flue, filters, controls, system flush and certification. Here's how the numbers break down.

Costs by boiler tier

What drives the variation

• Brand and warranty length — premium brands often include 10-year warranties (Worcester Bosch 12 years with installer accreditation, Viessmann 10 years standard, Vaillant 10 years on Exclusive range)
• Output rating — a 24 kW combi suits a flat or small house; 30–35 kW for a typical family home; 42 kW+ for larger homes or higher flow rate
• System flush — proper power flush typically £350–£500, magnetic flush £150–£250. Skipping this can void warranty.
• Flue routing — vertical flues, plume-management kits, or routes through unusual roof structures add cost
• Filters and controls — modern installs should include a magnetic filter (£100–£150), and Boiler Plus regs require a smart or compensating control on combis
• Boiler relocation — moving the boiler from one room to another adds £400–£900

Combi vs system vs regular pricing

• Combi → Combi like-for-like: £1,800–£3,500
• System → System like-for-like: £2,200–£3,800 (cylinder usually retained unless old)
• Regular → Regular like-for-like: £2,000–£3,500 (tank stays in loft)
• Regular → Combi conversion (remove tanks, reroute pipework): £3,000–£5,000+
• Regular / System → Combi in a multi-bathroom home — often a poor choice (combi can't handle multiple simultaneous draws); consider a system boiler with unvented cylinder instead

What should be in your quote

• Boiler make, model, output (kW), efficiency rating (≥92% ErP minimum)
• Warranty length and registration responsibility
• System flush method (power flush, magnetic flush, chemical clean)
• Magnetic system filter
• Programmer / smart thermostat (Boiler Plus requirement)
• Flue and accessories (vertical, horizontal, plume kit if needed)
• Gas Safe registration number and engineer ID
• Benchmark Logbook entry (manufacturer warranty requirement)
• VAT (20%) shown as a line item, not hidden in the totals
• Building Control notification via competent person scheme

Common surcharges

• Boiler relocation (combi to kitchen, garage to airing cupboard, etc.) — £400–£900
• Gas supply upgrade if your existing gas pipe is undersized — £200–£500
• Condensate routing if no suitable drain nearby — £150–£400
• Flue extension or plume management — £100–£350
• Asbestos removal in older boiler housings — £200–£800
• Hot water cylinder replacement (system boilers) — £600–£1,400

The "fixed price online quote" trade-off

Online providers (BOXT, Heatable, Octopus Heating, British Gas Online) offer fixed-price combi swaps starting at £1,800–£2,500. Convenience is real — instant quote, online booking, next-week install. The trade-offs:

• Limited to combi-to-combi like-for-like in most cases
• System flush typically magnetic, not full power flush
• Only one or two boiler brands offered
• Some surcharges only revealed on the engineer's pre-install survey

For straightforward combi swaps in mainstream property, the online route is genuinely competitive. For anything non-standard (conversions, relocations, system boilers with cylinder issues), a local independent Gas Safe engineer is usually a better fit and price.

Annual service costs

Once installed, expect £70–£120/year for an annual service from an independent Gas Safe engineer. Manufacturer services (Worcester Bosch, Vaillant, Baxi direct) typically cost £129–£180/year but maintain the warranty under their own terms.

Most boiler warranties (5–12 years depending on brand) require an annual service to be valid. Skipping services voids the warranty — false economy for a £100/year saving.