If a sealed heating system repeatedly loses pressure, record what changes and arrange competent help instead of continually topping it up. A single low reading does not identify the fault, and repeated repressurising can hide useful evidence.

Follow the boiler manual for any user control. Do not remove the boiler case, tighten internal components or use sealant products without professional advice.

First decide whether it is urgent

Turn the appliance off and seek prompt advice if water is reaching electrical equipment, there is significant leakage, the boiler displays an unsafe condition, or the manufacturer’s instructions tell you to stop. If you smell gas or a carbon-monoxide alarm sounds, leave the property and use the official emergency route; loss of water pressure is not the issue to investigate yourself.

For a small, stable pressure change with no other warning signs, collect information for the engineer.

What the gauge can tell you

Many sealed systems show pressure on a dial or display. The normal range and repressurising method depend on the model, so use the official manual rather than a generic internet number.

Do not wait beside an unsafe appliance simply to complete the table.

Why there may be no visible indoor leak

Water can escape slowly from pipework or emitters, at a concealed joint, or through a discharge route outside. Pressure can also vary because of a system component rather than a visible leak. These possibilities require diagnosis; the gauge pattern alone cannot distinguish them reliably.

Check only accessible areas without dismantling anything: around visible radiator valves, exposed pipe joints and beneath the boiler. Note staining or dampness but do not assume the nearest mark is the source.

Repressurising is not a repair

Some boiler manuals allow the user to restore pressure through a filling arrangement. If yours does, follow that model’s instructions exactly and stop at the stated setting. If you are unsure, cannot identify the controls or pressure falls again, arrange an engineer.

Frequent top-ups introduce fresh water into the system and can conceal the recurrence. Do not create a universal schedule such as “once a month is normal”; a system that needs repeated intervention deserves assessment.

What to tell the engineer

Provide the make, model, serial number, pressure photos, timeline, recent work and any visible discharge or water. Mention whether the system was recently bled, drained, serviced or altered. If a contractor previously repaired a leak, include the invoice and location.

This evidence can shorten diagnosis without pretending to identify the failed part.

Frequently asked questions

How often is too often to top up pressure?

There is no safe universal interval. If pressure repeatedly falls below the model’s normal range, or you need to restore it more than as a one-off after explained work, ask a competent engineer to investigate.

Can pressure fall without a visible leak?

Yes. The loss may be small, concealed or routed outside, or the pressure change may involve another system component. Absence of a puddle does not prove the system is sound.

Suggested on-page component

Use a Pressure Observation Log with date, cold reading, hot reading, refill, visible-water location and photo fields. It must not diagnose a component or tell users to open the boiler.

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