Fix low boiler pressure.

Low boiler pressure is the most common UK boiler complaint — typically caused by small leaks or bleeding radiators. It often appears as the boiler dropping out, or the pressure gauge showing under 1.0 bar. This guide covers the DIY fix, when to call an engineer, and what the actual repair costs.

Why Pressure Drops

• Recently bled radiators — air replaced with new system water needed.
• Small leak in pipework, radiator, or boiler.
• Faulty pressure release valve releasing system water.
• Expansion vessel failed (less common).
• Auto air vent stuck open.

DIY Fix (Re-pressurise)

1. Turn off boiler.
2. Locate the filling loop (usually under the boiler — silver braided hose).
3. Open both filling loop valves slowly.
4. Watch the pressure gauge — fill to between 1.0 and 1.5 bar (cold pressure).
5. Close both valves tightly.
6. Restart boiler and check it fires.

When to Call an Engineer

• Pressure drops again within a week — leak.
• Visible water marks on radiators, walls, or under boiler.
• Filling loop missing or broken.
• Repressurising doesn't restore boiler operation.

Typical Costs of Repair

UK Regulations

• Gas Safe Registration required for boiler repair work.
• DIY repressurise is fine; gas work or internal boiler work isn't.

Common Problems

• Over-pressurising — above 2 bar triggers PRV; releases water; pressure drops again.
• Filling loop left open — system over-pressurises.
• Repeated low pressure — there's a leak somewhere.

Frequently Asked Questions