Why does my boiler lose pressure overnight

A boiler is a common and important appliance in UK homes, especially in winters but sometimes you might experience that your boiler is getting cool or your boiler loses pressure overnight, which can be a frustrating situation for your daily routine and comfort. There may be a different reason behind this issue, like-

A little leak that becomes more apparent as the system cools

A component that has trouble maintaining pressure following a heating cycle

Pressure is being released (sometimes outdoors) and is only discovered later. 

1.Common Causes Boilers Lose Pressure Overnight

There are some common reasons behind your boiler losing pressure overnight, like-

1) A Small Hidden Leak

A tiny undercover leak can be a reason that you never see, and that is hidden in any unwatched place, like-

• Radiator valves (particularly TRVs)

• Inner boiler parts

• Pipe joints underneath floors or behind units

The reason it may feel "overnight" is that when the system cools, joints and seals might loosen, and little rips may become more readily apparent.

2) Faulty Expansion Vessel (EV)

A faulty expansion vessel can be a reason because the expansion vessel works to soak up pressure differences when water gets heated and cools. You may see some differences, like-

• Pressure increases when the heating is on.

• Pressure falls as the system cools (usually overnight)

• Regular pressure changes across a day

Expert understanding: One of the most common explanations for repeated pressure loss is a defective or empty expansion vessel. It also sometimes leads a PRV to begin discharging. 

3) Passing water from the Pressure Relief Valve (PRV)

You need to check the small copper pipe outside because the haggard PRV may discharge water during pressure points. You may see some signs, like-

• Stains or drops may indicate the release of pressure.

• After heating cycles, loss frequently appears, and the gauge seems low the next morning. 

4) Air in the System

Air pockets in the system can be a reason for boiler pressure loss, which can be in different spaces, like-

• Inequality of force pressure

• False low-pressure readings should come first.

• Appear upon radiator bleeding or filling up

This is typically a symptom rather than the underlying reason, particularly if you regularly top up. 

2.Is It Risky If Boiler Pressure Keeps Dropping?

Although low pressure by itself is typically not harmful, its source may be. If left unchecked, it may result in:

Shutdowns of boilers

Corrosion inside

Damage to heat exchangers

Expensive malfunctions throughout the winter 

3.When You Should Call a Professional

You should call an expert to handle the issue when you see any of these signs, like-

• The Pressure Drops Immediately: There can be a possibility for leakage if the gauge of your boiler goes into the red zone within an hour of re-pressurising,

• You Guess a Leak but can't See It: If you have doubts about a leak but you are unable to find it, then you should call because only a specialist has the tools to find it.

• Visible Water Damage Near the Boiler: If there are drips or rust stains signs from the boiler, then take it as an indication to call a professional.