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.
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Further Reading
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