Boilers & Heating
Immersion heater replacement
TL;DR
An immersion heater swap is £160–£280 including a decent-quality Incoloy element (not the cheap copper one that fails in 3 years). Takes 60–90 minutes if the old one comes out cleanly; longer if it's seized in a scaled-up cylinder. For unvented cylinders in hard-water areas fit a titanium element (+£40) — it'll outlast three copper ones. If both immersion and cylinder are 15+ years old, replacing the cylinder is often the smarter spend.
The immersion heater is the backup electric element in your hot water cylinder — sometimes the primary source if you're on Economy 7. When it fails you either get no hot water at all (if it's your only source) or you're forced onto boiler-only, which usually reveals a second problem you didn't know about.
This page covers when to swap the element, when to swap the whole cylinder, and why the £14 copper element from a shed is usually a false economy.
Fixed £50 diagnostic
Flat fee. No hourly meter running.
Fair quote or refund
Transparent pricing — refunded if we don't fix it.
Vetted UK engineers
DBS-checked, insured, real reviews.
AI-triaged in seconds
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How do I know the immersion has failed?
Three fault patterns. First: no hot water from the immersion at all — either the element's burned out, the thermostat's failed, or the switched spur has tripped. Second: the immersion trips the RCD every time you switch it on — element has cracked and shorting to earth, replace immediately. Third: water comes through lukewarm but never gets hot — either the thermostat is stuck low or the element is heavily scaled and no longer transferring heat efficiently.
- No heat at all — burned-out element or failed thermostat
- Trips the RCD every time — cracked element, earth fault, urgent
- Lukewarm only — scaled element or thermostat stuck at low setting
- Making a rumbling noise when on — scale build-up on the element
- Circuit-breaker holds but no heat — element continuity failed
Copper vs Incoloy vs titanium — which element?
The £14 copper element from a merchant is fine for a soft-water area on a vented cylinder — expect 5–8 years. In a Northwest medium-hard water area on a vented cylinder, fit an Incoloy element (£28–£45) — expect 10–15 years. In an unvented cylinder in hard water, fit titanium (£65–£95) — expect 15+ years and no scale build-up. The upgrade cost is trivial versus the cost of pulling the immersion again in 3 years.
- Copper — soft water, vented cylinder only, 5–8 year life
- Incoloy 825 — medium-hard water, vented, 10–15 year life
- Titanium — hard water, unvented, 15+ year life, zero scale grip
- Twin-element (top + bottom) — for larger cylinders with Economy 7
- Correct length — full-length element for the cylinder height
What we do on the visit
Isolate the electrical supply at the fused spur, drain the cylinder just below the immersion boss, unscrew the old element (special box spanner, often needs penetrating oil for seized elements), inspect the sacrificial anode if fitted, fit the new element with a fresh gasket, refill and vent, reconnect wiring, test the thermostat setpoint, and check the RCD holds under load. On unvented cylinders we also check the expansion vessel charge while we're on it.
When to swap the whole cylinder instead
If your cylinder is 20+ years old, single-wall copper (rather than modern stainless), leaking anywhere on the shell, or vented with a loft tank you're planning to remove anyway — spend the money on a new unvented cylinder instead. A £220 immersion swap on a 25-year-old cylinder is money you'll spend again inside 5 years when the cylinder itself gives up.
Typical prices
Real-world ranges from recent Northwest jobs. Your final price is confirmed in writing before any work starts.
| Item | Typical price | Notes |
|---|---|---|
| Immersion swap — copper element (soft water) | 160 – 220 | Vented cylinders only |
| Immersion swap — Incoloy element | 180 – 260 | Recommended for Northwest hard water |
| Immersion swap — titanium element | 220 – 320 | Unvented / hard water — 15yr+ life |
| Thermostat replacement only | 95 – 145 | If element is fine |
| Twin immersion swap (top + bottom) | 260 – 380 | Economy 7 cylinders |
| Seized-element removal surcharge | 40 – 80 | Only if genuinely stuck |
| Emergency same-day call-out | 140 – 200 | Plus parts and labour |
Which brand should you fit?
We fit Backer and Santon UK-made Incoloy 825 elements as our default, with titanium options from Backer for unvented and hard-water applications. Thermostats are Cotherm or Backer. All elements are BEAB-approved and carry a 2-year manufacturer warranty. We install and service Worcester Bosch, Vaillant, Ideal, Baxi, Viessmann and Alpha — none of them pay us commission and we don't push a "boiler of the month".
Immersion swap red flags
This is a quick job that some firms use to upsell. Ask these before you agree the price.
- What element are you fitting — copper, Incoloy or titanium?
- Is the price fixed regardless of how long the old one takes to remove?
- Are you draining just below the boss, or the whole cylinder unnecessarily?
- Will you check the thermostat and the switched spur at the same time?
- If the cylinder is old, are you being honest about repair-vs-replace?
- Is a new gasket included?
- What warranty on the element and the fitting?
Our promise on this job
Flat £50 diagnostic — deducted in full from any work booked. Fair, transparent quote before we start. If we can't fix the fault we diagnosed, we refund the diagnostic. All gas work is signed off by a Gas Safe registered engineer.
Talk to KJ about immersion heater replacement
Real triage in seconds. £50 diagnostic visit — refunded if we don't fix it.