Boiler interlock
In plumbing
An arrangement of controls that stops the boiler firing when no room or cylinder thermostat is calling for heat. Without it, a boiler can keep cycling on and off, wasting fuel, even when every room and the stored hot water are already warm enough.
Using Boiler interlock in a plumbing system
Updated
A distinction worth remembering
Where a radiator is cold points to the fix: air at the top, sludge at the bottom, a valve when it is cold all over, and balancing when only the far rooms lag. Controls then decide when the heat runs and how warm each room gets.
Questions to take further
- Is replacing a boiler notifiable work?
- In England and Wales, yes. An installer registered with a competent person scheme notifies it, or building control is told before work starts. Scotland and Northern Ireland run their own systems, and the gas work goes to a Gas Safe registered engineer.
Sources
- GOV.UK: Approved Document L — Guidance for England on energy efficiency, including heating controls when a boiler is replaced; guidance is not itself the legislation.
- HSE: domestic gas safety FAQs — Gas Safe registration and checking the categories of work on an engineer's ID card.
Where Boiler interlock fits in the learning path
The Central Heating section covers these topics:
- Wet Central Heating Systems
- Radiators and Heating Controls
- Heating Pressure and Safe Fault Checks
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- Radiators and Heating ControlsCentral Heating
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A control that switches the heating on and off to hold the air temperature set on it, measured where it is fitted. It works best on an inside wall away from radiators, sunlight and draughts. Turning it up higher does not warm a room faster; it only sets a higher target.
Room thermostat
Read the Room thermostat entryCompare related terms
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Room thermostat
A control that switches the heating on and off to hold the air temperature set on it, measured where it is fitted. It works best on an inside wall away from radiators, sunlight and draughts. Turning it up higher does not warm a room faster; it only sets a higher target.
Read the Room thermostat entryWeather compensation
A control that uses an outdoor sensor to set the heating's flow temperature: lower in mild weather, higher in cold. Cooler flow temperatures let a condensing boiler or a heat pump run more efficiently, and rooms tend to stay at a more even temperature through the day.
Read the Weather compensation 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.