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Iguana Heating and Plumbing LTD

Boiler Pressure – What Should It Be?

What should your boiler pressure be, and how to top up your boiler

If you have a problem with your boiler, the first thing to check is the pressure gauge. If your boiler turns off ununexpectedly or does not turn on at all, it may be due to a lack of water pressure in your system.

Without the correct water pressure in your heating system and boiler, it simply won’t be able to heat the water, and often has safety mechanisms to stop the boiler from coming on. If the pressure is too high, the boiler will also not come on.

How to check the pressure on your boiler

All boilers need the right amount of pressure to operate safely and effectively. If it’s not at the right level, your boiler won’t have the ability to do its job properly. Boiler pressure is measured by a pressure gauge, usually situated inside a panel or underneath your boiler.

Most combi and system boilers these days will have a built-in pressure gauge, so you can easily keep a check on your pressure levels. Your gauge may display pressure using a dial (a hydraulic pressure gauge) or, if you have a modern boiler installed, it’s probably a digital version. Either way, there will be a clear display of any warnings when your boiler pressure appears abnormal.

The pressure gauge will fluctuate slightly when the boiler is on and this is completely normal. If the pressure rises to greater than 2.5 Bar on the pressure gauge however it’s likely that your pressure vessel is not functioning as intended.

A rough guide on boiler pressure is:

  • 1 – 1.5 bar on the pressure gauge when the boiler is switched off.
  • Around 2 bars when the boiler is on.

How to top up my boiler pressure

If your pressure gauge is low, you will need to re-pressurise the boiler. This is a job you can easily do yourself by following these steps:

  • First off, make sure your boiler is turned off and completely cooled down.
  • You’ll then need to attach the filling loop. Different boilers require different methods here. Most boilers have a keyless filling loop, which will simply require you to pull a switch to add more water to your system. Others have a filling loop that resembles a hose, which is connected tightly to the two valves of your boiler. If you are unsure about the kind of filling loop your boiler has – check your boiler manual or call us on 01656 372144
  • Depending on your boiler type, you can open the valves to allow cold water from the mains to fill the boiler.
  • You should allow the boiler to fill up until your pressure levels appear normal (between 1 and 1.5 bar).
  • All that’s left to do is give your boiler a quick reset. Your boiler should then function correctly.


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