Heating Pressure and Safe Fault Checks
Central Heating · Plumbing
A sealed heating system tells you a lot through its pressure gauge. This topic explains what the readings mean, why heating water is treated, and which checks a householder can make before calling someone in.
The gauge is compared with the maker's range while the system is cold. Pressure that keeps dropping means water is escaping somewhere, while a big jump on heating up often means the expansion vessel has lost its air cushion; a drip from the outside discharge pipe shows the relief valve has opened.
Steel radiators slowly corrode, and the black magnetite that results clogs radiators, pumps and boilers. BS 7593 is the code of practice for cleaning and treating heating water with inhibitor, and a magnetic filter on the return catches what is left. Each top-up of fresh water weakens that treatment.
Power, timings, thermostat settings, the pressure gauge and bleeding sit on the householder side. Behind the casing, the gas valve, the burner and the flue are gas work: in Great Britain, refer them to a Gas Safe registered engineer.
The gauge and the discharge pipe tell the story
Updated
How to reason about the system
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.
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Learning content, not a qualification: it won't make you competent, certified or registered. Follow the regulations that apply and a qualified plumber before acting. About our content
Lessons on the plumbing path
- Reading and topping up pressure
- When pressure drops or rises
- Inhibitor, sludge and filters
- Safe checks and where to stop
Terms to know
Before 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.