Filling loop
In plumbing
A short connection between the mains cold supply and a sealed heating circuit, opened to add water when the pressure is low. A removable loop is taken off once the job is done, because it joins heating water to drinking water. Needing to add water often means a leak or a fault somewhere.
Using Filling loop in a plumbing system
Updated
A distinction worth remembering
Compare the cold reading with the maker's range, notice whether it falls over days or jumps when hot, and look outside for a dripping discharge pipe. Those three clues separate a leak from a vessel or valve fault.
Questions to take further
- Can I top up my boiler pressure myself?
- Many makers describe topping up a sealed system through the filling loop as a householder task. Follow the maker's instructions, top up cold, and get an engineer if it keeps dropping.
Sources
- Skills England: plumbing and domestic heating technician — The systems, materials, planning and customer responsibilities in the England occupational standard.
- HSE: domestic gas safety FAQs — Gas Safe registration and checking the categories of work on an engineer's ID card.
Where Filling loop 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
Read, practise, return
1. Read it in context
- Heating Pressure and Safe Fault ChecksCentral Heating
- Wet Central Heating SystemsCentral Heating
2. Try recalling, then explore practice
Use the memory prompt below to connect the vocabulary.
3. Return to the meaning
After reading or practising, explain the idea in your own words, then check what you remembered.
Recall a related term
Which term fits this definition? Say it to yourself, then reveal it. This is a memory prompt, with no score or saved result.
A heating system with no loft cistern, filled from the mains through a filling loop and kept under pressure. An expansion vessel absorbs the water's expansion as it heats, a gauge shows the pressure, and a relief valve opens if that pressure climbs too high.
Sealed heating system
Read the Sealed heating system entryCompare related terms
Open a meaning to compare its role with Filling loop, or follow its full entry.
Sealed heating system
A heating system with no loft cistern, filled from the mains through a filling loop and kept under pressure. An expansion vessel absorbs the water's expansion as it heats, a gauge shows the pressure, and a relief valve opens if that pressure climbs too high.
Read the Sealed heating system entryBackflow
Water flowing the opposite way to the one intended, for example from a hose left in a bucket, a cistern or an appliance back into the pipe that supplies drinking water. It can happen when the supply pressure drops, or when the system downstream is at a higher pressure. The water fittings rules in each UK nation require protection against it that matches the risk, judged by fluid category.
Read the Backflow 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.