Immersion heater
In plumbing
An electric element that sits inside a hot-water cylinder and heats the water directly, switched by its own thermostat. It is the main heat source in some homes and a backup in others. It runs from an electrical circuit, so a fault on the electrical side is a job for an electrician.
Using Immersion heater in a plumbing system
Updated
A distinction worth remembering
A cylinder fed from a cistern behaves differently from one sealed and fed from the main. Pressure, the parts on the inlet and the safety devices all follow from that one fact. Learn to tell the two apart and to see which faults belong to a competent unvented installer.
Questions to take further
- Is a dripping discharge pipe on an unvented cylinder a minor nuisance?
- No. It shows a relief valve is opening, so something in the system is not working as designed. The discharge route stays open and the fault goes to a competent installer.
Sources
- GOV.UK: Approved Document G — Guidance for England on hot-water safety, including stored hot water; guidance is not itself the legislation.
- Skills England: plumbing and domestic heating technician — The systems, materials, planning and customer responsibilities in the England occupational standard.
Where Immersion heater fits in the learning path
The Hot Water Systems section covers these topics:
- Hot Water Cylinders
- Combis and Instant Hot Water
- Hot Water Temperature Control
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- Hot Water CylindersHot Water Systems
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Recall a related term
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A hot-water cylinder heated by water from a boiler or heat pump flowing through a coil inside it. The heating water and the water drawn at the taps never mix. A direct cylinder, by contrast, heats its own stored water, for example with an immersion heater.
Indirect cylinder
Read the Indirect cylinder entryCompare related terms
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Indirect cylinder
A hot-water cylinder heated by water from a boiler or heat pump flowing through a coil inside it. The heating water and the water drawn at the taps never mix. A direct cylinder, by contrast, heats its own stored water, for example with an immersion heater.
Read the Indirect cylinder entryVented cylinder
A hot-water cylinder fed from a cold water storage cistern above it, with an open vent pipe that rises over that cistern. Its pressure comes from the height of the cistern, so outlets upstairs can run gently, and it does not carry the layered safety devices an unvented cylinder depends on.
Read the Vented cylinder entryBefore you start: some plumbing work is regulated or notifiable
Some water fittings work needs notice to, and consent from, the water supplier before it starts. Check the rules where you live.
Gas work is for competent workers covered by a Gas Safe registered business in Great Britain. Northern Ireland has separate gas regulations. Do not work on gas pipes or appliances yourself.
In England, installing an unvented hot-water system over 15 litres is notifiable building work: use a competent installer registered with a competent-person scheme, or tell building control before work starts. Leave this work to a suitably skilled person.
Wales, Scotland and Northern Ireland have their own water and building rules; check which apply before work starts. Electrical connections belong with an electrician.
This guide does not qualify you or make you competent, approved or registered for plumbing, gas or unvented work.
A definition is a start. Using it in a real question is where it sticks.