Plumber Cost to Replace a Boiler

You’ve woken up to that sound again—the ominous clunk from your airing cupboard. Or maybe your energy bills are creeping up like a slow-motion horror film. Either way, you’re facing the dreaded boiler replacement. But what’s this going to actually cost you? Let’s cut through the noise.

⚙️ Boiler Types: Your Wallet’s Biggest Decision

Combi boilers (compact, tank-free) are the UK’s favourite for a reason. They’re cheaper to install and ideal for smaller homes. But here’s the kicker:
Cost: £1,500–£4,500 installed.
Best for: 1–2 bathroom homes. Try a Worcester Bosch 30i (£1,100 unit) or Baxi 624 (£850 unit) if you’re budget-conscious.

System boilers need a cylinder but handle higher demand. Translation: fewer cold showers during the morning rush.
Cost: £1,700–£5,000 installed.
Watch out: Adding a new cylinder tacks on £500–£1,000.

Conventional boilers (with tanks in the loft) are the old‑school workhorses. Pricier but suit big, traditional homes.
Cost: £1,700–£5,500 installed.
Hidden headache: Tank replacements add £500–£1,500.

Back boiler conversions (old fireplace boilers → combi): £3,000–£5,000.

🔧 Installation: Where Quotes Get Complicated

A straight swap is easy. But these variables will nudge your bill higher:

Relocating the boiler: Add £300–£800. Loft installs? £500+.
Pipework upgrades: Going from 15mm to 22mm copper? £300–£500 extra.
System flushes: Power flushes cost £300–£750.

Labour costs: Londoners pay ~20% more. Outside capital: £325–£375/day. Inside: £410–£485/day.

🏷️ Brand Wars: Premium vs. Budget

Brand	Price Range	Perks
Worcester Bosch	£1,000–£2,500	10–12 year warranties, Which? Best Buys
Vaillant	£900–£2,200	Top-tier efficiency, 10-year cover
Baxi/Ideal	£700–£1,800	Solid mid-range, 5–10 year warranties
Glow-worm/Vokera	£400–£1,000	Budget upfront, but potential long‑term costs

💸 Hidden Costs You’ll Kick Yourself For Missing

Flue extensions/plume kits: £100–£200.
Smart thermostats (Hive, Nest): Reduce bills by ~35%.
Warranties: Premium include up to 10 years; budget often require add‑on £200+.
Biomass boilers: £10,000–£18,000; qualify for £7,500 BUS grants.

💰 How to Pay Without Panicking

Grants:

ECO4: Free boilers for low‑income households/EPC D–G.
Boiler Upgrade Scheme (BUS): £7,500 toward heat pumps or biomass.

Finance:
0% APR deals (e.g., James Frew) allow 1–10 year payback.

Pro tip: Local engineers sometimes skip VAT—£500–£1,500 cheaper than big firms.

💎 The Bottom Line?

Replacing a boiler in 2025 is a puzzle—home size, system type, and hidden extras matter. But with an A‑rated model, you could slash bills by ~£385/year.
Repair vs. replace? If it’s over 10 years old and repairs cost £1,000+, replacement is the better investment.
Quote tools: Services like Heatable or Boiler Central offer online fixed-price quotes—no calls, no hassle.

🛠️ How to drain boiler to replace expansion tank

Turn off and cool the boiler system.
Isolate the expansion tank using the valve on its feed pipe.
Attach a hose to the tank’s drain/drain valve.
Open the drain and/or vent to allow air in as water exits. Continue until air flows freely.
Shut the drain valve, open isolation valve, and repressurize system. Listen for water refilling tank.
Restore full system pressure, check for leaks, and return boiler to service.