Find out why your boiler keeps losing pressure

Work through the boiler, radiators and pipework in order to find why pressure keeps dropping, and know when to call an engineer.

AB-01Check and log the current pressureLook at the pressure gauge on the front of the boiler. Most boilers should read between 1 and 2 bar when the heating is cold, though check your boiler's manual for the exact figure. Write down today's date and reading on your phone or a notepad, so you can see how fast it drops over the next day or two.

AB-02Find your stopcock before you start checking for leaksIf you do find a leak later, you may need to shut the water off quickly. Find your stopcock now, usually under the kitchen sink, and turn it a quarter turn to check it moves freely. Turn it back and leave it alone unless you actually need it.

AB-03Inspect the boiler itself for damp or stainingWith a torch, look underneath and around the boiler casing for damp patches, drip marks, or a small puddle in the drip tray if it has one. Feel along the pipes entering the bottom of the boiler for dampness. Do not remove the boiler casing yourself, that part is for a Gas Safe engineer only.

RULES

1 each · Torch

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1 roll · Kitchen roll

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KNOW THE RULES

Only a Gas Safe registered engineer may open a boiler's casing or work on its gas or flue components. It is against the law for anyone else to do this, even to look inside.

AB-04Check every radiator valve and bleed screwGo round every radiator in the house. Wipe a piece of kitchen roll around each valve at both ends and around the bleed screw at the top. If the paper comes away wet or shows a rust-coloured mark, that valve is the likely source. Small weeps here are common and often just need the valve nut nipped up gently with a spanner.

1 roll · Kitchen roll

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1 each · Adjustable spanner

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AB-05Check the pressure relief valve discharge pipe outsideFind the small white or copper pipe that runs from the boiler out through an external wall, usually near ground level. If it is dripping, wet, or has a limescale trail below it, the pressure relief valve is letting go internally, which is a job for a Gas Safe engineer, not something to fix yourself.

RULES

KNOW THE RULES

A leaking pressure relief valve is an internal boiler fault. Diagnosing and repairing it is gas work and must be done by a Gas Safe registered engineer.

AB-06Check the filling loop for dripsFind the filling loop, usually a flexible braided hose with a tap or lever at each end, fitted under or beside the boiler. Check both connections and both valves for dampness or a slow drip. If it drips even when both valves are firmly closed, the loop itself may need replacing.

1 roll · Kitchen roll

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AB-07Top up the pressure if no leak was foundMake sure the heating is switched off and the boiler has cooled. Open both filling loop valves slowly until the gauge reads about 1.5 bar, then close both valves fully, tightest first. If the loop is detachable, unclip it once done. Never leave the filling loop open and connected after topping up.

AB-08Monitor the pressure over the next 24 to 48 hoursCheck the gauge again the next morning and evening, and write down each reading. A pressure that holds steady after topping up suggests the system just needed air out or a minor weep sorted. A pressure that keeps falling at a similar rate points to a leak you haven't spotted, or a fault inside the boiler.

AB-09Know when to call a Gas Safe registered engineerCall an engineer if pressure keeps dropping with no visible leak, if you found staining at the pressure relief pipe, or if you're not confident checking any of the above. Tell them your logged readings and dates, it helps them diagnose faster. Never attempt to open the boiler casing or work on its internal parts yourself.

RULES

KNOW THE RULES

Gas boiler repairs and internal inspections must legally be carried out by a Gas Safe registered engineer. This applies to the boiler itself, not to bleeding radiators or using the filling loop, which are normal homeowner tasks.

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