Your boiler pressure is dropping overnight, leaving you with low pressure or no heating in the morning.
Pressure drops to zero or below 1 bar by morning
Is this your problem?
What to do
• Check the pressure gauge when the boiler is cold (first thing in the morning).
• Normal cold pressure in the UK is 1.0–1.5 bar.
• If it’s below 1 bar, top up using the filling loop to about 1.3 bar, then stop.
• If pressure drops again within 24 hours, don’t keep topping up — that confirms a fault.
Pressure drops only when heating is on
Is this your problem?
What to do
- Turn heating on and watch the gauge for 10–15 minutes.
- If pressure falls while radiators heat up, air is likely trapped.
- Bleed radiators one by one (start downstairs).
- Recheck pressure and top up once only if needed.
- If bleeding doesn’t stabilise it, stop — something else is wrong.
- Pressure loss can cause the boiler to turn on and off repeatedly
Pressure drops overnight but no visible leaks
Is this your problem?
What to do
- Check every radiator valve, pipe joint, and under sinks for damp marks.
- Pay attention to hidden pipework (behind sofas, under floorboards).
- Small leaks often dry during the day and show overnight pressure loss.
- If nothing is visible, suspect an internal boiler leak — not DIY.
Pressure rises when heating is on, then drops after cooling
Is this your problem?
What to do
• This points to a failed expansion vessel (very common in UK boilers).
• Check if pressure climbs above 2.5 bar when hot, then drops cold.
• This is not homeowner-safe to fix.
• Continued use can damage the boiler.
Pressure drops after topping up, every single night
Is this your problem?
What to do
- Check the filling loop valves are fully closed (both sides).
- Even a slightly open valve can cause slow pressure loss.
- If the loop is closed properly and pressure still drops, stop topping up.
- Call a Gas Safe engineer — repeated refilling can crack components.
Is it safe to fix this yourself in the UK?
Safe DIY
• Checking the pressure gauge
• Bleeding radiators
• Topping up pressure once to 1.2–1.5 bar
• Checking visible pipe joints for leaks
Do NOT attempt
• Opening the boiler casing
• Touching the expansion vessel
• Adjusting internal valves
• Re-pressurising daily
When to stop immediately
• Pressure drops below 0.5 bar repeatedly
• Pressure shoots above 3 bar
• Boiler shows fault codes or shuts down
When to call a professional
• Pressure drops every night
• No visible leaks found
• Expansion vessel suspected
• Boiler is over 8–10 years old