# How much does a new boiler cost in Hertfordshire? *David · Founder, Datum · Datum · updated 2026-10-19 · Boilers* A like-for-like combi swap in Hertfordshire typically costs £2,310–£3,010 installed — including the boiler, flue, system flush, magnetic filter, controls, labour and VAT. For comparison, iHeat's fitted prices start at £1,945 including VAT and its August 2026 installs averaged £2,820, with the middle half between roughly £2,525 and £3,247. A conversion (say, system boiler to combi) runs higher — typically £3,200–£4,300 with us, and around £4,000 at iHeat — because pipework and cylinder removal are involved. A quote far below these ranges is worth questioning: ask what has been left out of the job or the price. ## What moves the price Four things move a boiler price: the boiler itself (brand, output and warranty length), the complexity of the swap (Worcester Bosch says installs usually take one to three days, with a straightforward like-for-like swap about a day), the flue, and relocation. What the survey finds behind the walls matters more than the postcode. A straight horizontal flue is cheap; a vertical flue through the roof adds roughly £200–£500 plus possible scaffolding, according to EnergyPages. Moving the boiler is priced by distance: iHeat's published relocation charges run from £495 to £895. ## The add-ons, priced honestly A magnetic system filter is £100–£200 fitted on its own, according to EnergyPages — we include one as standard because old-system sludge is exactly what it protects against. A power flush for a badly sludged system runs £300–£600 typically. A smart thermostat is a further, optional cost. An older 15mm gas supply pipe sometimes needs upgrading for a modern boiler — EnergyPages puts that at £200–£600 depending on the run. Good quotes name these items; bad quotes discover them mid-job. ## What should always be included The boiler and flue, a full system flush (not a rinse), a magnetic filter, controls set up and explained, making good, removal of the old boiler, Gas Safe certification, Building Regs notification and warranty registration, and a proper handover. If a quote is vague on any of these, ask — 'while we're here' extras are how cheap quotes become expensive jobs. ## How cheap quotes get cheap Mostly by leaving out things you won't notice until later: the flush and the filter, Building Control notification, warranty registration and the Benchmark commissioning checklist. Dwellow says a quote without a magnetic filter should be £150–£200 cheaper, the average cost of fitting one. None of it shows on install day; it shows later. Approved Document L says the central heating and primary hot water circuits should be thoroughly cleaned and flushed before a new heating appliance is installed, and Baxi says repairs caused by sludge are not covered by its warranties. Without the notification there is no certificate to show when you sell the house. ## Fixed price vs estimate An estimate can move; a fixed price can't. We survey first (free), then the price is fixed in writing — if something genuinely unforeseeable turns up mid-job, we stop and talk to you before anything changes. > If a quote lands far under these ranges for a proper swap, the money is coming from somewhere — usually the flush, the filter, or the paperwork that keeps your warranty alive. > > — David, Founder, Datum ## Related questions ### Is it cheaper to repair or replace an old boiler? If the boiler is under ~10 years old and the fault is a single component, repair usually wins. Beyond the 10 to 15 years Baxi gives for a boiler that is serviced annually, replacement often becomes the better spend — we'll give you both numbers honestly and let you choose. ### How long does a boiler swap take? A like-for-like combi swap is usually one day. Conversions and relocations run two to three days depending on pipework. ### Why do online quotes vary so much? Because they're pricing different jobs. iHeat's fitted prices start at £1,945 for a straightforward combi, yet its August 2026 installs averaged £2,820 once the boiler, flue, controls and cleaning suit the house. Compare what's included — flush, filter, controls, flue work, warranty years — not just the headline. ### Do new boilers come with a warranty? Yes — manufacturer warranties vary by brand, model and installer accreditation, and are confirmed in writing on your quote, along with what keeps them valid (registration at install, then an annual service). ### Does hard water in Hertfordshire really affect a new boiler? Affinity Water says the area it supplies has hard water (check your postcode with your water supplier), generally 300–350 mg/l (21–24 degrees Clark). Approved Document L says that in hard water areas suitable measures should be taken to treat the feed water to combination boilers to reduce limescale. We'll talk to you about scale protection honestly at the survey; the filter and proper flush deal with sludge. ## Sources & verification - [iHeat — New boiler costs (fitted prices from £1,945 including VAT for a combi; average installation £2,820 including VAT in August 2026, with the middle half between about £2,525 and £3,247; conversions around £4,000; relocation charges £495 to £895; updated 1 Oct 2026; accessed 19 Oct 2026)](https://www.iheat.co.uk/boiler-help/new-boiler-costs) - [EnergyPages — Boiler costs (magnetic filter £100–£200; power flush £300–£600 on older systems with sludge; vertical flue +£200–£500 plus possible scaffolding; upsizing an older gas supply pipe £200–£600 depending on the run; 24–30 kW suits most 3-bed homes and 30–35 kW a 4-bed with two bathrooms; oversizing burns more gas per cycle and shortens boiler life; accessed 19 Oct 2026)](https://energypages.co.uk/boilers/costs) - [Dwellow — Boiler change prices (a quote without a magnetic system filter should be £150–£200 cheaper, the average cost of fitting one; published 10 Feb 2026; accessed 19 Oct 2026)](https://www.dwellow.co.uk/guides/boiler-change-prices) - [Worcester Bosch — Step by step guide to boiler installation (usually 1–3 days; straightforward like-for-like swaps in about a day; accessed 19 Oct 2026)](https://www.worcester-bosch.co.uk/heating-advice/step-by-step-installation) - [GOV.UK — Approved Document L, volume 1: dwellings (before a new heating appliance is installed the central heating and primary hot water circuits should be thoroughly cleaned and flushed, a chemical inhibitor added, the feed water to combination boilers treated in hard water areas, and the system commissioned to BS 7593 — paragraph 8.8 of the 2021 edition incorporating 2023 amendments, 7.8 of the 2026 edition; a replacement gas boiler in an existing dwelling should meet 92% ErP efficiency, or in exceptional circumstances 78% SEDBUK; accessed 19 Oct 2026)](https://www.gov.uk/government/publications/conservation-of-fuel-and-power-approved-document-l) - [Affinity Water — retailer water quality guidance, 23 Apr 2021 ("the area supplied by Affinity Water has 'hard' water", a general range of 300 to 350 mg/l or 21–24 degrees Clark; check your postcode on their website; accessed 19 Oct 2026)](https://www.affinitywater.co.uk/docs/wholesale/Wholesale-WQRetailer-guidance.pdf) - [Baxi — How do I know if I've got sludge in my central heating system? (radiators hot at the top and cold at the bottom; a system that gurgles and kettles; have the system water cleaned and fit a magnetic filter, cleaned at the annual service; repairs caused by sludge are not covered by Baxi warranties; accessed 19 Oct 2026)](https://www.baxi.co.uk/help-and-advice/faqs/how-do-i-know-if-ive-got-sludge-in-my-central-heating-system) - [Baxi — How long does a boiler last? ("10 to 15 years if you have it serviced annually and look after it properly"; accessed 19 Oct 2026)](https://www.baxi.co.uk/help-and-advice/faqs/how-long-does-a-boiler-last) --- Canonical page: https://www.datumclimate.co.uk/guides/new-boiler-cost-hertfordshire