Home  >  Advice Centre   >   What Pressure Should My Boiler Be At?

What Pressure Should My Boiler Be At?


Boilers are responsive to extreme pressure changes. When boiler pressure is too high or too low, the boiler automatically shuts down, and your home ends up without central heating or hot water.

To help you avoid such a scenario, we have created a comprehensive guide on boiler pressure to explain the various acceptable pressure ranges.

How Do I Check My Boiler’s Pressure?

Different models of boilers are customised differently depending on the manufacturer. Most gas boilers will have a gauge with distinct green and red regions. The green zone typically represents the optimal region, while red represents the low and high-pressure regions.

Other boilers are fitted with two needles, one red and one black.  The red needle indicates where the pressure ought to be, while the black points to the current reading of the pressure. A few brands display pressure on an LCD screen or show an error message when the current pressure is too high or too low.

What Is The Ideal Pressure My Boiler Should Be At?

For optimum operating conditions, the pressure on a boiler should read between 1 and 2 bars. Many manufacturers recommend 1.3 bars as the ideal boiler pressure, but this value can vary, so be sure to check your owner’s manual.

What Pressure Should My Boiler Be At When The Heating Is Off?

When the central heating is turned off, the pressure gauge on your boiler should indicate a value between 1 and 1.5 bars. Many boiler models will have a pressure reading of 1.3 bars when cold, but this figure can vary. Nonetheless, the pressure value should remain above the lower limit indicated by the manufacturer, which is typically 1 bar. As always, do check your owner’s manual for precise values since different models have different specifications.

What Pressure Should My Boiler Be At When The Heating Is On?

When the heating system is on, your boiler’s pressure should read a value in the region of 1.5 to 2 bars. Most models highlight this zone on the pressure gauge in green and mark regions beyond 2 bar in red. Some boilers give an allowance of up to 2.5 bars when heating is on, but generally, beyond 2.75 bars means excess pressure. However, it is advisable to refer to your owner’s manual to get the correct value assigned to your boiler.

Why Does My Boiler’s Pressure Increase As It Heats Up and Drop As It Cools?

The answer is quite simple. Water, like most substances, expands when heated and contracts when cooled. As the boiler heats the water in the central heating system, the water expands in volume and results in a steady increase in boiler pressure.

Even though the boiler pressure can rise above the upper limit for your boiler model, there is no need to be alarmed. As you turn off the heating system, the water will contract, and the pressure will gradually decrease until it reaches the optimal value.

However, one thing to note is that a single heating cycle shouldn’t induce an increase of 1bar or higher in boiler pressure. If it does, then chances are your boiler has a faulty expansion vessel or pressure release valve.

What Causes My Boiler Pressure To Drop?

Low boiler pressure can be attributed to the following:

  1. Water leaks.
  2. Bleeding radiators.
  3. Faulty pressure relief valve on the boiler.
  4. Dodgy expansion vessels.
  5. The Pressure gauge on the boiler is faulty.

How Can I Fix Low Boiler Pressure?

  1. If you suspect that the low boiler pressure results from water leaks in the system, it is advisable to contact a qualified gas technician to fix it. Alternatively, you can opt to fix it yourself using a sealant, as long as you can trace the leak area.
  2. Re-pressurise the boiler by letting more water into the system through the filling loop. It is advisable to check your manual before attempting to re-pressurize your boiler, but here is an essential guide.
  • Turn off your boiler and allow for cooling
  • Find the filling loop
  • Ensure you can clearly see the pressure gauge
  • Open the valves on both sides of the boiler to let water into the system
  • Allow water to flow in until the needle on the pressure gauge indicates 1.5 bars
  • Close both valves
  • Turn on your boiler and press the reset button

Why Is My Boiler Pressure Too High?

Reasons for a high boiler pressure may be:

  1. Too much water in the system since there is a tendency to let in excess water when adding water due to low pressure.
  2. The external filling device might be faulty, allowing water to pass through the closed valve, resulting in continuous pressure rise.

How Can I Fix High Boiler Pressure?

If you suspect that an internal malfunction causes the high pressure in your boiler, it is advisable to contact a certified gas engineer. However, if the high pressure is caused by excess water in the system, you can fix it yourself. All you need to do is bleed water from the system through the towel rails.

To bleed the excess water, insert the bleed key, open the valve slowly and let the water drip out. After some time, close the valve using the bleed key, and check for optimal pressure. Repeat this process until you attain the desirable outcome.

Is Low Boiler Pressure Dangerous?

Low boiler pressure is not hazardous. Water leaks from the system slowly, and while you may not notice the slight changes in pressure, over time, the pressure falls till it is too low and the boiler shuts down.

Is High Boiler Pressure Dangerous?

High boiler pressure is not dangerous. The heating system has a pressure relief valve (PRV) that prevents damage by letting water escape via a small pipe through the external wall near the boiler. Most boilers also shut down when the pressure is too high, thus avoiding damages.

  • Buy Now Pay Later Schemes!
    • Interest Free Credit
    • Buy Now Pay Later
    • Spread Payments
    Finance Options
  • Free Boiler Quotes

    No-obligation to buy!

    • From the comfort of your home
    • You choose the best company
    • Gas Safe trusted companies
    Get Quote NOW
Need a New Boiler

Get FREE quotes from tradesmen in your area today. What are you looking for?