What bar should my boiler be?

Question

Does the boiler pressure change at different times of the year? I'm not sure if the boiler pressure is getting low. What should it be at when running and then when off as well?

Orrin · Answer

Between 1 - 1.5 bar when boiler is cold. pressure will rise when a demand is put on the boiler.

Joe · Answer

Between 1-1.5 when cold .

When running the pressure should fluctuate any more than 2 bar ideally

Liam · Answer

Usually between 1 and 1.5 bar when cold. This pressure will rise with expansion when the system is hot.

Farhan · Answer

It should be between 1 to 2Bar ( green line) if it’s dropping or rising too fast then there must some issue. 
Thanks

Bob · Answer

You should set your pressure at1bar and when boiler is running you will see pressure go up and drop but as long as it stays on 1 bar when  not running you will be fine

Ben · Answer

Between 1 and 1.5 bar when the boiler is cold.
Your manufacturer's instructions should cover it. If you don't have them, you can download them from the manufacturer.

Curtis · Answer

Yes — boiler pressure does change with the seasons, and what you’re noticing is completely normal to a point.
🌡️ Why it changes
Your heating system is sealed and filled with water. When it heats up, the water expands; when it cools down, it contracts. So:
In winter (heating on a lot): pressure tends to run higher
In summer (heating mostly off): pressure often looks lower
🔧 What the pressure should be
For most UK combi or system boilers:
When the system is cold (heating off):
👉 Around 1.0 – 1.5 bar (ideal is ~1.2 bar)
When the heating is on (hot):
👉 Around 1.5 – 2.0 bar
A slight rise when the heating kicks in is exactly what you want to see.
⚠️ What’s not normal
Below ~0.8 bar (cold):
Pressure is too low — the boiler may stop working or need topping up
Above ~2.5–3 bar (hot):
Too high — could indicate an issue (like expansion vessel problems)
Big swings (e.g. 1.0 bar cold → 2.8+ hot):
Often a sign the expansion vessel needs checking
💡 Seasonal example
Summer (heating off most of the time): might sit around 1.0 bar
Winter (regular heating use): might rise to 1.6–1.8 bar when running
That’s perfectly fine.
🛠️ When to top it up
You should only need to top up (using the filling loop) if:
It drops below ~1.0 bar when cold
Or the boiler shows a low-pressure warning

Michael · Answer

When the boiler is off pressure should be between 1/1.5. When it is on this can goto 2bar due to exspaion

Riccardo · Answer

1-1.5 cold and around 2-2.5 bar when running. 
Doesn’t need to change for different periods of the year. Most boilers won’t run unless they have at least 1 bar.

Altin · Answer

Pressure on the boiler should be Between 1.2 to 1.5 bar Best.

What bar should my boiler be?

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