Use your own manufacturer’s instructions for the acceptable readings and any permitted user action. Record when pressure changes and any safely visible leaks. Repeated pressure loss should be investigated.
Gas smell or suspected carbon monoxide?
Get outside into fresh air and call 0800 111 999 from a safe place. Do not wait for an online booking. Read emergency guidance
Compare like with like.
Tell the engineer whether the reading was taken with the heating cold or running. Note roughly how quickly it falls and whether it rises significantly when heating starts. Those details are more useful than changing the pressure immediately before every check.
A low reading does not identify a failed part.
The cause could involve more than one part of the system. There may be a visible leak, or the issue may require professional investigation. This page cannot establish the cause from a single gauge reading and does not recommend a part to replace by guesswork.
Do not apply a universal filling instruction.
Boilers and filling arrangements differ. Follow only the homeowner procedure for the specific appliance and system, and stop if you cannot confidently identify what it describes. Do not keep adding water to hide recurring loss or interfere with a safety valve or discharge pipe.
Photographs can help.
A clear image of the display and safely accessible damp areas can assist the enquiry. Do not remove a boiler cover, climb into an unsafe area or reach near electrical equipment to get a better photograph. Describe any recent radiator work or servicing.
Book diagnosis when the problem returns.
A standard service is not the same as tracing a recurring pressure problem. Arrange diagnosis / repair, explain the pattern and keep the observations available. Any further work is quoted after the cause is assessed.
Useful official guidance
General information does not replace the instructions for your appliance or an inspection of your home.
Worcester Bosch: boiler pressureHSE: gas safety at home