Twin Coil Cylinder Installation London
Future-proofed hot water cylinders for solar thermal, air source heat pumps and boiler-paired systems. G3 qualified engineers across every London borough. Fitted from £2,195 inc. VAT — Building Regulations Part G3 notification and Benchmark logbook included on every install.
Telford Tempest, Joule Cyclone, Gledhill StainlessLite Plus, OSO Super S and Range Tribune specialists. MCS-compliant heat pump pairings under the £7,500 BUS grant.
A twin coil cylinder is an unvented hot water tank with two internal heat exchangers — one for a renewable source (solar thermal, heat pump or wood-burner) and one for a conventional boiler. It is the right cylinder spec for any London home pairing a boiler with solar, planning a heat pump retrofit under the £7,500 BUS grant, or fitting a back-boiler. ERL installs twin coils from £2,195 fitted with full G3 commissioning and Building Regulations notification. Call 0207 046 1363.
What is a twin coil cylinder?
A twin coil cylinder is an indirect, unvented hot water store with two separate heat-exchanger coils built into the tank. The lower coil — sized larger than the upper — is tied to a renewable or pre-heat source: solar thermal panels, an air source heat pump, a wood-burner back-boiler, or even surplus PV electricity through a power diverter. The upper coil is tied to a conventional gas, oil or electric boiler that tops the stored water up to set point whenever the renewable contribution falls short.
Each coil runs in its own sealed primary loop with its own pump, controls and (on solar systems) glycol antifreeze. The two heat sources never mix at the primary level — they only meet inside the water that sits in the cylinder. Differential temperature controllers and stat positioning ensure the renewable source always gets first call on heating the water before the boiler fires. That hierarchy is the whole reason the spec exists: it puts the free or low-cost energy in first, and uses the boiler only as a top-up.
In London the twin coil cylinder has gone from a niche spec to the smart default on three job types: boiler-and-solar pairings, heat pump retrofits under the £7,500 BUS grant, and future-proofed boiler swaps where the homeowner wants the option to add a renewable in 5–10 years without ripping the cylinder out again. For a full picture of the cylinder market and where twin coil sits, see our hot water cylinder replacement guide.
Five ways London homes use a twin coil cylinder
The twin coil is a flexible bit of kit. Same cylinder, very different jobs depending on what is plumbed into the lower coil. Here are the five configurations we install across London the most often.
Solar thermal + gas boiler
Lower coil tied to a roof-mounted flat plate or evacuated tube array. Upper coil tied to a system or heat-only gas boiler. The cylinder banks solar gain through the day; the boiler tops up to set point only when the solar contribution falls short. Typical London 4-panel install delivers 50–60% of annual hot water demand for free.
Best for homes with south-facing roof pitch and £4–7k solar budget
Air source heat pump + immersion backup
Lower coil sized for low-grade heat pump flow (typically 45–55°C). Upper coil unused or piped as an immersion bypass loop. Pairs with MCS-certified heat pumps under BUS grant — cylinder must meet MIS 3005 sizing rules (3.0 m² coil surface, 200L minimum on most homes).
Required for BUS £7,500 heat pump grant compliance
Boiler + solid fuel / wood stove back-boiler
Upper coil from gas/oil boiler, lower coil from a wood-burner or biomass back-boiler with gravity-circulated thermal store. Common in period London townhouses with restored Victorian fireplaces. Needs an open-vented neutralising header on the solid-fuel side under Building Regs J.
Suits listed and period properties with original solid fuel features
Future-proofed boiler install
Lower coil left capped and pre-plumbed for a future solar or heat pump retrofit. Adds £400–£600 to the install cost today but saves £1,800–£2,400 in re-routing pipework and lifting floorboards when the renewable is added in years to come. The smart default for new boiler installs in London.
Adds £400–£600 today, saves £2k+ on later retrofits
Twin boiler / cascade system
Two boilers feeding a single twin-coil cylinder — typically used on larger HMOs, B&Bs and small commercial sites where redundancy and peak load shaving matter. Each boiler runs its own coil so one can be isolated for service without losing hot water.
Used on HMO, B&B and small commercial cylinders
Brand comparison — twin coil cylinders fitted in London
Six cylinder brands cover 95% of the London twin coil market. The key spec to look at is the lower coil surface area — that determines whether the cylinder will work with solar thermal, a heat pump under MCS rules, or both.
| Brand | Sizes | Coil area | Warranty | Notes |
|---|---|---|---|---|
| Telford Tempest Twin Coil | 120L–500L | Lower 2.5 m² / upper 0.8 m² | 25 yr tank · 2 yr parts | Strongest UK twin-coil reputation. Generous lower coil makes it the standard for solar retrofits across London. Stocked by every major merchant. |
| Joule Cyclone Twin Solar | 170L–500L | Lower 3.0 m² / upper 1.0 m² | 25 yr tank · 5 yr parts | Irish-made duplex stainless. Oversized lower coil and longer parts warranty. Best technical choice for heat pump pairing under MCS rules. |
| Gledhill StainlessLite Plus Solar | 150L–300L | Lower 2.4 m² / upper 0.9 m² | 25 yr tank · 2 yr parts | Best recovery time of the mid-range duplex cylinders. UK manufactured in Blackpool. Common in new-build London apartments with solar PV-T tie-ins. |
| Range Tribune HE Solar | 150L–300L | Lower 1.8 m² / upper 0.8 m² | 25 yr tank · 2 yr parts | Value choice. Smaller solar coil so less efficient on bigger arrays. Fine for 2-panel solar thermal or pre-plumbed future-proof installs. |
| OSO Super S Twin | 200L–400L | Lower 2.7 m² / upper 1.1 m² | 25 yr tank · 2 yr parts | Norwegian-built premium cylinder. Best build quality and standing heat loss figures. Fitted on the higher-end Kensington and Hampstead jobs. |
| Kingspan Albion Ultrasteel Twin | 180L–300L | Lower 2.5 m² / upper 0.9 m² | 25 yr tank · 2 yr parts | Tridex stainless construction. Good middle-ground option. Pre-bonded sensor pockets save commissioning time on solar pairings. |
Twin coil cylinder sizing — London homes
Sizing follows the Hot Water Association rule of 35–45 litres per person plus 50 litres per daily-used bath. Heat pump pairings push the minimum size up because MCS standard MIS 3005 sets a 200L floor on most ASHP installs. Solar arrays want bigger lower coils.
| Property | Bathrooms | Occupants | Recommended | Notes |
|---|---|---|---|---|
| 1–2 bed flat | 1 bathroom | 1–2 | 150L–170L | Solar tie-in possible on a flat roof; check planning |
| 2–3 bed flat / terrace | 1 bathroom | 2–3 | 180L | Sweet spot for solar pre-heat retrofits |
| 3-bed terrace | 1–2 bathrooms | 3–4 | 210L | Pair with 4-panel solar array for ~55% annual coverage |
| 4-bed semi / townhouse | 2 bathrooms | 4–5 | 250L | MCS minimum size for ASHP under BUS grant |
| 5+ bed family / HMO | 2–3 bathrooms | 5+ | 300L | Twin coil + secondary circulation typical |
| Mansion block / large HMO | 3+ bathrooms | 6+ | 400L+ | Cascade or commercial sizing — call for survey |
Twin coil cylinder cost London — 2026 prices
Every quote is a fixed figure given in writing after survey. No call-out fee on quoted work, no parking add-ons, no out-of-hours premium on scheduled installs. Prices include the cylinder, full G3 inlet group, expansion vessel, T&P relief, discharge pipework, Benchmark commissioning and Building Regulations notification.
| Job | What's included | Typical cost |
|---|---|---|
| Twin coil cylinder — 180L (3-bed terrace) | Supply & fit indirect twin-coil unvented cylinder, dual primary connections (boiler + solar/HP), G3 inlet group, expansion vessel, T&P, discharge to outside, Building Regs notification, Benchmark logbook. | From £2,195 |
| Twin coil cylinder — 210L (3–4 bed, 2 bath) | Supply & fit 210L stainless steel twin-coil unit, both primary loops piped in 22 mm copper, secondary anti-Legionella stat on lower coil, full G3 commissioning. | From £2,395 |
| Twin coil cylinder — 250L (4–5 bed family) | Supply & fit 250L duplex stainless cylinder, oversized lower coil for solar / heat pump pre-heat, upper coil for boiler top-up, full safety group, certificate posted. | From £2,695 |
| Twin coil cylinder — 300L (large home / HMO) | Supply & fit 300L twin-coil cylinder, secondary circulation provisions, enhanced insulation jacket, dual coil flow balancing, building control sign-off. | From £2,995 |
| Solar thermal pre-plumb add-on | Add solar pump station, 2-port motorised diverter, solar differential controller, flow group and stat pocket wiring on a new twin-coil install (cylinder day). | From £895 |
| Heat pump compatibility upgrade | Upsize lower coil to a 3.0 m² heat-pump-rated surface area, fit weather compensation provision, MCS-compliant pipework sizing, primary insulation to Part L. | From £495 |
| Vented twin-coil → unvented conversion | Remove old vented cylinder + loft tank, fit new unvented twin-coil, run new discharge to outside, expansion vessel, primary repipe, full G3 cert. | From £2,895 |
| Annual G3 service (twin-coil cylinder) | Both coils flow-tested, expansion vessel pre-charge reset, T&P witnessed lift, PRV outlet pressure logged, anode inspected, Benchmark refreshed. | £165–£235 |
* Prices include VAT and Building Regulations G3 notification. See the full pricing page for adjacent work.
Need a fixed-price quote on a twin coil install?
Call 0207 046 1363Our 5-step install process
Survey & specification
30 min on siteG3 engineer attends, measures cupboard or plant room, checks cold mains static and dynamic pressure, confirms discharge route to outside, agrees coil sizes against renewable source (solar / heat pump / future-proof). Fixed written quote issued same visit.
Removal & first-fix
2–3 hoursOld cylinder drained, isolated and removed. Loft tank (if vented) decommissioned. New 22 mm copper primary loops run for both coils. Discharge pipework prepared from tundish to external termination. Call 0207 046 1363 for a same-week booking.
Cylinder placement & second-fix
2 hoursNew twin-coil cylinder positioned, levelled, inlet group fitted (combined PRV, check valve, expansion vessel, drain), upper coil tied to boiler primary, lower coil tied to solar / heat pump primary or capped for future retrofit.
Electrical & controls
1 hourCylinder thermostats fitted to both coils, dual zone controls wired, motorised diverter valves connected, anti-Legionella schedule set on lower coil, immersion isolator and RCD verified, all wiring to BS 7671 18th Edition.
Commissioning & certificate
1 hourSystem pressurised to 3.0–3.5 bar, both coils flow-tested under load, T&P witnessed-lifted, expansion vessel pre-charge set, full Benchmark logbook completed, Building Regulations G3 notification filed via Competent Person Scheme. Certificate posted within 30 days.
G3 compliance and Benchmark commissioning
Every unvented twin coil cylinder install in England and Wales is a controlled service under Approved Document G3 of the Building Regulations. The engineer must hold a current G3 ticket (BPEC, LCL Awards or City & Guilds 6035 — renewed every five years) and the work must be notified to Building Control. ERL self-certifies through the Competent Persons Scheme (WaterSafe / BESCA) so the compliance certificate is posted directly to the property owner within 30 days.
On top of G3, the install is documented in the manufacturer's Benchmark logbook — the commissioning record required to validate the 25-year cylinder tank warranty. Skipping the Benchmark step is the single most common reason warranty claims get refused. Here's what we record on every twin coil commission.
Cylinder data plate logged
Serial number, manufacturer, model, capacity and date of manufacture transcribed into Benchmark — required for the 25-year tank warranty.
Cold inlet pressure recorded
Static and dynamic mains pressure measured at the inlet group. Minimum 1.5 bar dynamic on most twin-coil cylinders. Below 1.5 bar requires a cold accumulator vessel.
PRV outlet pressure set
Pressure reducing valve adjusted to 3.0–3.5 bar to match cylinder rating. Locked off and logged on the Benchmark certificate.
Expansion vessel pre-charge
Vessel charged to manufacturer-stated pressure (typically 3.0 bar) before any water hits the system. Re-tested annually as part of the G3 service.
T&P relief valve witness test
Manual lift test on the 90°C / 7 bar safety valve. Reseat checked. Discharge confirmed flowing freely to a visible external termination.
Both coil flow & return temps
Upper and lower coil flow / return temperatures logged against the heat source — boiler at 70°C, heat pump at 45–55°C, solar at 60–80°C depending on insolation.
Cylinder stats calibrated
Both cylinder thermostats set: upper coil stat to 60°C (anti-Legionella safe), lower coil stat to 55°C (renewable source). Cut-outs witness-tested.
Discharge pipe inspection
Tundish 300 mm air gap confirmed. Discharge pipe sized one size larger than T&P, continuous fall, no more than three bends, terminates externally at low level.
Building Control notification
G3 install notified via our Competent Persons Scheme (WaterSafe / BESCA) within 30 days. Compliance Certificate posted to property owner direct from the scheme.
Real London twin coil jobs — worked examples
Six anonymised twin coil jobs from the last twelve months — the brief, the cylinder fitted, the renewable pairing and the final invoice figure.
Edwardian semi, Hampstead — solar thermal retrofit
Owner installed a 4-panel evacuated tube solar array on a south-facing rear roof. Old 180L single-coil Heatrae Sadia stripped, replaced with a 250L Joule Cyclone Twin (3.0 m² lower coil). Lower coil piped to the solar pump station, upper coil retained on the existing Worcester 30CDi system boiler. Commissioned with a Resol DeltaSol differential controller. Annual solar contribution measured at 58% across year one. Cost: £4,895 inc. solar pump station (cylinder element £2,695).
1960s mid-terrace, Wandsworth — heat pump BUS grant install
Air source heat pump replacing an end-of-life gas boiler under the £7,500 BUS grant. MCS rules required a minimum 200L cylinder with a 3.0 m² lower coil. Fitted a 250L Telford Tempest Twin with the lower coil tied to the new Mitsubishi Ecodan, upper coil retained as immersion backup. Full MIS 3005 compliance pack prepared. Cylinder cost: £2,795 inc. VAT (heat pump quoted separately).
Victorian townhouse, Kensington — future-proofed boiler swap
Boiler upgrade with the owner planning a heat pump in 5–7 years. Fitted a 210L twin-coil at boiler day rather than a single-coil. Lower coil capped at the cylinder, pre-plumbed to a wall plate inside the plant room so the future heat pump primary can land without lifting floors. Boiler day cost premium: £495 over single-coil. Saves an estimated £2,200 on the future retrofit.
Listed townhouse, Bloomsbury — back-boiler + boiler
Restored Victorian fireplace with a wood-burner back-boiler. Twin-coil cylinder lets the wood stove pre-heat the water via gravity circulation on the lower coil, with the gas system boiler topping up via the upper coil only when needed. Cylinder: 300L Telford Tempest Twin. Open-vented neutralising header fitted on the solid-fuel side per Building Regs J. Cost: £3,495 inc. VAT.
HMO conversion, Hackney — twin boiler cascade
10-bed HMO with two 24 kW system boilers feeding a single 400L twin-coil cylinder for redundancy. Each boiler runs its own coil so the property never loses hot water during boiler service. Secondary circulation loop fitted with bronze pump on a timed control. Cost: £6,295 inc. VAT for the cylinder + pipework package.
Top-floor flat, Fulham — solar PV-T tie-in
Hybrid solar PV-T panels generating both electricity and heat. Lower coil of a 180L Gledhill StainlessLite Plus tied to the PV-T thermal circuit, controlled by a Solic 200 power diverter routing surplus PV to the immersion. Effectively three heat inputs (PV-T thermal, surplus PV electric, gas boiler) into one cylinder. Cost: £2,395 inc. VAT.
Planning a solar, heat pump or future-proofed cylinder install?
Free on-site survey, fixed written quote, G3 qualified engineers, full Building Regulations notification, 25-year tank warranty preserved. Average install slot inside 7–10 days. Call 0207 046 1363 or message on WhatsApp.
Areas covered across London
Twin coil cylinder installs across every London borough. Heaviest call volumes for solar pairings in Camden, Islington and Hackney; heat pump retrofits concentrated in Wandsworth, Hammersmith & Fulham and Barnet; future-proofed boiler swaps across Westminster and Kensington & Chelsea.
Frequently asked questions
What is a twin coil cylinder?
How much does twin coil cylinder installation cost in London?
Do I need a twin coil cylinder for solar thermal?
Can I use a twin coil cylinder with a heat pump?
What size twin coil cylinder do I need?
Do I need a G3 ticket to install a twin coil cylinder?
How long does a twin coil cylinder install take?
Will the upper and lower coils ever heat the same water?
Can a twin coil cylinder be future-proofed for solar or heat pump later?
What is the difference between twin coil and twin port?
Do twin coil cylinders need a different annual service?
Will my old vented cylinder pipework work for a twin coil unvented?
Is the cylinder coil capacity warranty different to the tank warranty?
Can I have a twin coil cylinder in a top-floor London flat?
How does the controller know which coil to use first?
Question not answered? Call 0207 046 1363 and speak to a G3 engineer directly — no call centre, no triage.
Service area
Twin coil installs across all London boroughs
G3 qualified cylinder engineers based in central London with same-week install slots across all 32 London boroughs and the City. Average survey-to-install lead time is 7–10 working days for booked twin coil jobs.
Ready to spec a twin coil cylinder?
Free on-site survey, fixed written quote, G3 qualified engineers, full Building Regulations notification, 25-year tank warranty preserved. Solar, heat pump and future-proofed boiler pairings. £5M public liability, fully insured.
London 247 Home Services Ltd · Company No. 17120057 · £5M public liability · G3 qualified · 24/7 emergency line