If you’ve looked at your boiler display and seen a pressure reading, you may be wondering whether it’s normal.
For many sealed central heating systems, the boiler pressure will usually sit at around 1 to 1.5 bar when the system is cold, although you should always follow the manufacturer’s instructions for your particular boiler.
If the pressure is significantly lower or higher than expected, there may be an issue that needs investigating.
Boiler pressure is the pressure of the water circulating through a sealed central heating system.
You’ll normally see it displayed on a pressure gauge or digital display on the boiler.
It is not the same thing as the pressure of water coming into your property from the mains.
This distinction is particularly important when you’re considering a combi boiler.
For many modern sealed systems, a cold pressure of around 1–1.5 bar is typical.
Energy Saving Trust also gives 1–1.5 bar as the usual range for boiler pressure and recommends checking the manufacturer’s instructions for your particular system.
When the heating is running, the pressure may rise.
If it falls outside the normal range, check your boiler’s instructions before taking action.
There are several possible reasons.
When you bleed a radiator, air leaves the heating system and some water can also be lost.
This can cause the system pressure to fall.
A persistent pressure drop can indicate a leak somewhere in the heating system.
This may be visible around radiators, valves or pipework, but leaks aren’t always obvious.
A sealed heating system contains an expansion vessel that allows for the expansion of water as it heats.
If the vessel isn’t working correctly, pressure can fluctuate abnormally.
Some boiler faults can cause pressure problems.
If you’re repeatedly having to repressurise the system, don’t simply keep topping it up. The underlying cause should be investigated.
Low pressure means there isn’t enough water pressure within the sealed heating circuit.
A boiler may stop working or display a fault code when the pressure becomes too low.
A small drop after bleeding radiators isn’t unusual, but repeated pressure loss isn’t something to ignore.
High pressure can occur for several reasons.
If the pressure is consistently too high, or rises significantly when the heating comes on, the system should be checked by a qualified engineer.
Don’t assume that simply releasing pressure will solve the problem.
No.
This is particularly important when comparing boiler systems.
A combi boiler takes its hot water directly from the mains supply, so incoming mains flow and pressure can have a major effect on shower and tap performance.
Boiler pressure refers to the closed heating circuit.
If you’re considering a new combi boiler, an installer should assess the mains water supply before recommending a model.
A powerful combi boiler cannot create unlimited water flow if the incoming mains supply cannot provide it.
This is one reason a combi that works perfectly in one property may not be the best choice for another.
Energy Saving Trust identifies low water pressure as one of the situations where a combi may be less suitable.
The short answer
For many sealed heating systems, around 1–1.5 bar when cold is normal.
A small change can be perfectly normal, but persistent pressure loss, very high pressure or large fluctuations should be investigated.
And remember: boiler pressure and mains water pressure are two different things.
Not necessarily. Around 1–1.5 bar is commonly recommended for many sealed systems when cold, but always check your boiler manufacturer’s guidance.
It may be above the normal cold pressure range for many systems. Check the manufacturer’s instructions, particularly if the pressure continues to rise.
Possible causes include a leak, bleeding radiators, a problem with the expansion vessel or another system fault.
No. A combi uses the property’s incoming mains water supply. It cannot increase the underlying mains flow available to the property.
The required pressure and flow depend on the boiler and installation, but the incoming mains supply should be assessed before choosing a combi.
If you repeatedly need to repressurise the boiler, the cause should be investigated rather than repeatedly topping it up.
