New 16A radial circuits, fault-find on existing immersions, element and thermostat replacement, dual-element Economy 7 / Octopus Cosy off-peak time clocks, full hot-water cylinder re-wires. Test gear on the van — insulation resistance and continuity to diagnose in minutes. From £140 + VAT @ 20%.
07889 334849 · Dan Stevens
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BS 7671A 3kW immersion heater is a heavy continuous load — you do not put it on a shared ring. The standard build is a dedicated radial circuit from the consumer unit terminating in a switched fused connection unit (FCU) next to the cylinder, with the immersion’s flex tail wired to a flex outlet plate. Dual-element tanks get two of those, often with a programmable time clock controlling the bottom element for off-peak heating.
Single-element 3kW immersion: dedicated 16A radial from the consumer unit, 2.5mm² twin-and-earth cable, 30mA RCD-protected. Never sharing with other circuits.
Double-pole switched FCU within easy reach of the cylinder, fused at 13A. Flex outlet plate next to it, with the immersion’s heat-resistant flex tail terminated through a stuffing gland.
Dual-element cylinders get two circuits — one to the top, one to the bottom. The bottom element runs on a time clock during off-peak hours (Economy 7 / Octopus Cosy). Top is a daytime boost.
Real DS Electrical install — dedicated immersion circuit on a 30mA RCBO, terminated to a switched FCU at the cylinder.
Whether it’s a fault-find on a tripping immersion or a brand-new dual-element setup with off-peak time clock, the standard is the same. Dedicated circuit, RCD-protected, double-pole isolation at the cylinder, written certificate. No shortcuts on hot water.
If it’s a fault, we test before we quote — insulation resistance, continuity, thermostat function. You get a written diagnosis and a fixed price for the fix, not a guess.
3kW continuous load gets its own circuit — never shared with sockets or anything else. 2.5mm² cable, 16A RCBO, 30mA RCD protection. To BS 7671.
Switched fused connection unit at the cylinder — double-pole so both live and neutral are broken on isolation. Anyone can kill the immersion before service work.
Immersion flex is exposed to high cylinder-top temperatures — we fit proper heat-resistant rubber flex (HOFR or similar), not standard PVC, terminated through a flex outlet plate.
Programmable 7-day clock for Economy 7 / Octopus Cosy windows. We program it in front of you, label it clearly, and walk you through how to change it.
Insulation resistance, continuity, polarity, RCD trip time, Zs — all measured. Minor Works Certificate or EIC issued same day, in your inbox before we leave.
Final price depends on cable run length, board capacity, what’s actually wrong (for fault-finds), and whether you need a single-element or dual-element setup. Survey is free; written quote is fixed. Read the disclaimer below the cards before assuming.
Same-day fault-finds on tripping or cold immersions, planned upgrades to dual-element Economy 7 setups, full cylinder re-wires when an old cupboard is a mess of junction boxes and dodgy isolation. Wells, Bath, Frome and the surrounding Mid Somerset villages.
Both fail commonly, often together. The thermostat is usually the cheaper, easier fix — a stuck thermostat can either give no heat at all or cook the tank constantly. A failed element typically reads open-circuit on a continuity test or shows insulation breakdown to earth (which trips the RCD). We carry test gear on the van — insulation resistance test plus continuity will tell us inside ten minutes which it is, often both. Replacement is usually a same-visit job if we’ve got the right element on the van.
A dual-element cylinder has two immersion heaters: a top element and a bottom element. The bottom element heats the whole tank during cheap off-peak hours (Economy 7, Octopus Cosy etc.). The top element is a daytime boost — it only heats the top third or so for a quick top-up at peak rates. Done right, you wash with off-peak water at a fraction of the daytime tariff. Worth fitting if you’re on a time-of-use tariff and your tank already supports it; otherwise a single-element setup is fine.
Yes. We fit a programmable time clock (typically a 7-day digital model) wired so the immersion only switches on during your tariff’s off-peak window — usually a 7-hour overnight slot for Economy 7, or the cheap windows you choose for Octopus Cosy. We can wire it as the sole supply (timer always governs) or in parallel with a manual override boost so you can force a daytime heat if needed. We label everything clearly so you don’t have to remember which switch does what.
A standard 3kW immersion runs on a dedicated 16A radial circuit, 2.5mm² twin-and-earth cable from the consumer unit, on a 16A MCB or RCBO with 30mA RCD protection. The supply terminates at a double-pole switched fused connection unit (FCU) within easy reach of the cylinder, with a flex outlet plate from there to the immersion’s flex tail. Dual-element tanks need two of those circuits — one per element — both on their own RCBOs.
The most common cause is element insulation breakdown — moisture or limescale gets through the element sheath and creates a leakage path to earth. An insulation resistance test (Megger) at 500V between live conductors and earth will show the value drop towards zero. Less commonly: damaged flex, water in the FCU, or a failed thermostat shorting to the casing. Whatever the cause, do not just keep resetting the RCD — that’s unsafe. Get it tested. We’ll diagnose, quote and replace the same visit where possible.
For a well-insulated modern cylinder on a flat tariff, two or three timed boosts a day usually beats leaving it on continuously — but the difference is smaller than people think because the thermostat cycles anyway. On Economy 7 / Octopus Cosy, the answer is clear: heat the whole tank overnight on the cheap rate, then top up if needed during the day. Time clock pays for itself quickly on a time-of-use tariff. We’ll talk you through the maths on the survey.
Most immersion faults are diagnosed inside half an hour with proper test gear. Same-visit element or thermostat replacement where we can. Free survey, fixed quote, NAPIT certified.
07889 334849