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What Should My Boiler Pressure Be? Signs Pressure Is Too High/Low

Boiler pressure gauge

Boilers are sensitive to pressure issues — they can lock out when they lose too much pressure, or when the boiler pressure is too high. So, if you’re wondering what should the boiler pressure be, you’re in the right place. Our quick guide will explain the ideal boiler pressure when the appliance is hot, cold, the optimal working pressure, and how to spot a problem.

It doesn’t matter whether you have a Worcester, Vaillant, Baxi or other brand of boiler — the correct boiler pressure is similar across various brands and models.

If you need a Gas Safe registered engineer for boiler repairs, you can book one here. Or, if you’re tired of your old and unreliable boiler, you can get fixed prices for a replacement on-screen using this form.

What pressure should my boiler be when it’s cold?

The normal boiler pressure when the central heating system has cold water should be between 1 and 1.5 bar. Most manufacturers recommend an optimal system pressure of 1.3 bar .

That said, if you’re asking yourself “What should the boiler pressure be when the heating is off?”, the best thing to do is refer to your boiler manual — the recommendations may differ between manufacturers.

Should a boiler increase in pressure as it heats up?

The answer is yes, your boiler pressure increases as the central heating system water heats up. You can monitor this increase by looking at the boiler’s pressure gauge dial, which is usually located on the boiler display panel (or just below the boiler casing on some older boilers, such as Ferrolis).

What pressure should my boiler be at when it’s hot?

Generally, it’s completely normal if the boiler bar pressure rises by around 0.3-0.5 bar when the heating is on. So, the ideal boiler pressure should be in the 1.5-1.8 bar range when the water is hot.

Why does the water pressure gauge increase when the heating is on?

The pressure on your boiler’s gauge will increase when the heating is on. This surge in operating pressure is caused by water expansion, which occurs naturally as the boiler heats water circulating through the pipes, radiators, and towel rails.

That said, your boiler pressure rise shouldn’t amount to more than 1 bar during the heating cycle. If your boiler pressure goes up more than 1 bar (or close to 1 bar) during start-up, there’s probably a fault with the expansion vessel or the pressure relief valve.

What to Do When…

Boiler Pressure Is Too Low

If your boiler is losing pressure, it may lock out and you’ll have to reset it. To do so, you’ll have to repressurise, or increase boiler pressure.

Learning how to repressurise the boiler isn’t hard: simply add water to the system via the external filling loop. This should resolve your low boiler pressure issue — unless there’s a leak in the boiler or the heating system.

Boiler Pressure Keeps Dropping

If you’ve repressurised the boiler, but still observe the boiler pressure dropping, it’s a sign of a leak. The low pressure will persist unless you fix the leak first. You can figure out why your boiler is losing pressure and leaking here.

Boiler Pressure Is Too High

So, your boiler pressure is too high; what do you do now?

There’s a good chance you’ve recently topped up the pressure a bit too much — and that’s why you have abnormally high boiler pressure.

If you have, you can reduce boiler pressure by bleeding water from the system via the towel rails as a quick-fix. You’ll need to get a radiator key, a bucket or tub, and some towels. Once you’ve got them, here’s what you do:

  1. Insert the bleed key and open the valve slowly until it starts dribbling water.
  2. Close the bleed valve using the key and check the pressure.
  3. Repeat until you get to optimal pressure.

If you drain too much pressure from the system, you can top it up by using the filling loop to add more water to the system.

In the event that the fixes above don’t help restore the ideal boiler pressure, you should get in touch with a Gas Safe engineer and have them inspect your faulty boiler. You can do that here.

Or, would you prefer a quote for a new boiler installation? Head to this form from Heatable, and you’ll get a fixed price quote on your screen in minutes.

What’s Next?

We hope our guide to the ideal boiler pressure will help you spot problems with your boiler before they deteriorate. If you have any questions, or would like to share your experience with boiler pressure issues, please leave our readers and us a comment below.




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  1. David says:

    I have changed the expansion tank, pressure overflow valve, auto air vent, and the pressure overflow valve still is dripping. adjusted the reduceing valve two turns.
    problem persist, what’s a home owner to do?

    1. Alex Ion says:

      I think you need to have the engineer back and check things out for you again.

  2. Valerie Swaney says:

    If I have my boiler set to come on when temperature drops but my water pressure drops to zero will it still come on.maybe a daft question and I am taking it the answer would be no but having disagreement with gas supplier as my gas bill.is very extreme.

    Thank you

    1. Alex Ion says:

      Most likely the boiler will throw in an error 🙂

  3. Mr L Spink says:

    My boiler is showing high pressure 3 bar when not in use .
    There is a trickling water sound which i think is from the condensate line.
    The pressure drops when I run hot water (2.5 Bar) but returns to 3 bar when i turn off the water and the boiler stops.
    I have tried venting the system back to 2 bar but just goes back to 3 when in use.
    The boiler is a Greenstar 25SI/30SI fitted 2006
    The only problem before this was pressure falling to zero which a new PRV was
    fitted and some sort of sealing fluid put into the system.

    1. Alex Ion says:

      Try to throw some water out. Leave it on for more when you’re venting. You can leave it working at 2bar, no problem.

  4. muriel nicklin says:

    got a worc boch why when i try to run a bath the water is luke warm and have to run water for ages in the kitchen to get so hot water it runs warm then cold then warm and after about 10minuets hot enought to wash up

    1. Alex Ion says:

      I’d check the boiler with an engineer. There can be many things.

  5. Scott Templeton says:

    The pressure on my boiler says 1.3 on the digital readout cool. But the analogue gauge that replenishes the pressure says 1.7. Which one is correct???

    1. Alex Ion says:

      It’s always tricky with these. We tend to trust digital readings more than analogue.

  6. Brian says:

    My boiler pressure is well into the green section at 1 bar but when not operating at night it drops into the red section? Does this matter?

    1. Alex Ion says:

      I would pump in a bit more, make it 1.5bar.

  7. Lilian Smith says:

    I don’t have a red and green zone so which us the needle to keep at 1.5 the black or the red needle? On boiler for electric central heating

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