Swindon · Wiltshire

Boiler Losing Pressure? Causes and Safe Fixes

Low pressure is the most common "my boiler's broken" call in winter, and often the simplest fix.

Normal, low, high

• Normal cold pressure: 1.0–2.0 bar on the gauge.
• Below 0.5–1.0 bar: most modern boilers lock out.
• Above 3.0 bar: the pressure relief valve may discharge water outside.

The safe repressurise routine

1. Turn the boiler off and let it cool. 2. Find the filling loop (a braided hose with one or two valves under the boiler). 3. Open the valve(s) slowly until the gauge reads ~1.2–1.5 bar. 4. Close the valves firmly, restart, and watch the gauge for ten minutes.

Your boiler's manual has the exact procedure for its model; if you cannot find it, the manufacturer publishes manuals online. If you are unsure at any point, stop and call an engineer.

If pressure keeps dropping

You have a leak or a failed component:

• Radiator valves or pipework — check for damp patches and corrosion.
• Pressure relief valve (PRV) — recurring discharge from the outside pipe points here.
• Expansion vessel — pressure swings high then low; needs an engineer.
• Underfloor leak — pressure loss with no visible leak and warm spots on floors needs urgent attention.