Ideal boiler pressure

How to Repressurise Ideal Boiler Pressure

Last updated on February 19th, 2024

When your boiler pressure drops too low the boiler will stop working which means you will have no heating or hot water.

Ideal boiler pressure should be between 1 and 1.5 bar on the pressure gauge when the radiators are cold.

I have been repairing and servicing boilers full-time for over a decade and pressure fixes are very common.

Ideal Boiler Pressure

If your Ideal boiler pressure is under 1 bar then you should increase the pressure.

Repressurise Ideal boiler

If your boiler pressure is over 1.5 bar when the system is cold, then you should reduce the pressure.

Boiler Pressure When Heating is On

The boiler pressure when the heating is on can rise to over 2 bar. This is perfectly normal as the heat expands the water inside the central heating system when the heating is turned on.

How to Check Pressure

You need to find the pressure gauge to check the pressure on an Ideal boiler.

Boiler Pressure Too Low

Low boiler pressure is very common and can cause your boiler to stop working. If your pressure becomes too low then you need to repressurise it.

Boiler Losing Pressure

Your Ideal boiler keeps losing pressure most likely for one of these reasons:

  • A Leak on the central heating system
  • The expansion vessel has lost its air
  • Pressure relief valve passing water
  • Filling loop open

A leaking boiler is the most likely cause of the loss of pressure.

How to Repressurise an Ideal Boiler

If your pressure drops below 1 bar, you might get the Ideal boiler F1 fault code, you will need to increase the pressure.

To increase the pressure you must:

  1. Open one valve fully (only if there are two valves)
  2. Open the other valve slowly until you can hear the water
  3. When the pressure has reached 1 to 1.5 bar close both valves
  4. Reset the boiler (if needed)
  5. Turn the heating on

Do not open both filling loop valves fully straight away as the water pressure in the house might be too much for the boiler and cause the Baxi boiler pressure to shoot up too much.

How to increase the pressure on an Ideal boiler

Boiler Pressure Too High

Your boiler pressure is too high most likely for one of these reasons:

  • Somebody repressurised the boiler too much: Reduce pressure in the boiler by letting water out
  • The expansion vessel has lost air or the diaphragm inside is split: Recharge the expansion vessel or possibly replace
  • The filling loop is not closed fully or damaged: Close the filling loop fully or replace it
  • Pinhole leak on plate heat exchanger on a combi boiler: Replace the plate heat exchanger

How to Reduce the Pressure

To reduce the boiler pressure when it’s too high, you must let some water out of the heating system.

Here are the 5 best ways to reduce the pressure:

  • Bleed a radiator
  • Open a drain off valve
  • Open the pressure relief valve
  • Crack a nut
  • Open the magnetic filter

Bleed a Radiator

The easiest way to do this is to bleed the radiators using a radiator bleed key.

bleeding water out of a radiator
Bleeding water out of a radiator

You should bleed all the air out of all the radiators. When there is no air left, you can bleed the water out of one radiator until the pressure drops to around 1 to 1.5 bar.

Put a towel or two down on the floor under the radiator and catch the water squirting out into a bucket.

Open a Drain Off Valve

Most central heating systems have at least one drain-off valve.

Drain down hose on drain off valve
Hose on a drain off valve

You can find them on radiator valves, radiator pipes, and on the bottom of boilers. They are for draining water out of the central heating system.

You can connect a hose to a drain-off valve using a hose clamp and run the pipe to an outside drain or down the toilet or sink, then open the square nut using an adjustable spanner until the water starts coming out.

Keep checking the pressure gauge on the boiler until it has dropped to around 1 to 1.5 bar.

Open The Pressure Relief Valve

Another way to reduce boiler pressure without bleeding radiators is to open the pressure relief valve.

combi boiler pressure relief valve
Pressure relief valve

A pressure relief valve (PRV) is on every pressurised central heating system.

They are usually inside the boiler but could potentially be in the hot water cylinder cupboard.

You simply turn it anti-clockwise (or pull the lever on some boilers), and the pressure will drop very quickly.

This is the easiest way to reduce boiler pressure without bleeding radiators and the most common way I do it when I’m on a job.

The only problem with opening the pressure relief valve is that once they’ve opened they might not close again properly.

This will tend to happen on dirty systems but 9 times out of 10 it’s fine. If it does happen, you need to fit a new PRV.

Crack a Nut

Cracking a nut is another way to lower the pressure without bleeding radiators when your boiler pressure is too high. This is one of the messiest ways to do it but it is possible.

You can put towels and a bucket under a nut on the boiler, radiator valves, or anywhere on the central heating pipes.

How to reduce boiler pressure
Cracking nut on radiator valve

Then crack the nut until water starts coming out and keep an eye on the boiler pressure gauge.

Magnetic Filter

It is also possible to reduce boiler pressure via the central heating magnetic filter.

You should place a towel and bucket underneath the magnetic filter then open the nut on the bottom (if it has one) or you can open the bleed valve with a bleed key.

Magnaclean Pro 2 Fitted
Magnetic filter

Let the water come out into the bucket and close it when the pressure gauge has dropped to around 1 to 1.5 bar when the system is cold.

Ideal Boiler Guides


If your Ideal boiler pressure is too low or too high then fixing this is important. Repressurising a boiler is an easy job. It can save you from having to pay a plumber to do such an easy task.

If you have to keep repressurising your boiler, you should get that problem found and fixed as soon as possible.

Feel free to ask me any questions in the comment section below and I’ll do my best to help.

Please share this post if you find it helpful.


  • Steven Reid

    I am a full-time plumber and Gas Safe registered engineer. I incorporated Housewarm Ltd. in 2011 to provide heating and plumbing services to homes in Newcastle upon Tyne, England. I now blog about what I've learned over the years to help DIYers and plumbers.

    View all posts
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4 thoughts on “How to Repressurise Ideal Boiler Pressure”

  1. andrew thornton

    Great advice, but my boiler only has two black taps and a yellow gas tap. i’ve tried to open both the black taps but the pressure doesn’t move and i can’t hear the water moving. i have the Ideal logic system s30.

    1. Steven Reid

      Hi Andrew, the filling loop will be elsewhere on a system boiler as there’s no water supply at the boiler. It’s usually in the hot water cylinder cupboard.

  2. Brian Crake

    Your article is spot on. We had a problem with topping up the system every day but that was solved when I replaced some pvc pipework in the loft.

    However, I now have a different problem. When we get a F1 fault and the gauge is at zero. If we top it up (the way you suggest) if we crack the closed loop value just a tiny bit, I mean a tiny bit, the pressure shoots right up.

    What do you think ?

    1. Steven Reid

      Hi Brian,
      Sounds like the expansion vessel has no air in it. It might need to be recharged or possibly replaced.
      More info here

      It could also be the small hose inside the the boiler which connects the expansion vessel to the heating system, this can get blocked on dirty heating systems and is a nightmare to replace as you have to strip half the boiler down.

      I would rule out the expansion vessel first though.

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