How to repressurise a boiler

If your central heating system isn’t running as it should be, it could be because your boiler needs to be repressurised.

If your boiler pressure is either too low or too high, this can cause issues such as no hot water, a leaking radiator or poor heating efficiency.

Here, we will help you through the process of repressurising your boiler.

How to check your boiler pressure

For most modern boilers, including combi boilers, the pressure gauge can be found under the control panel.

If you have an older boiler, you may find the boiler pressure gauge underneath the boiler, next to the pipework. The location of your pressure gauge will be in your handbook.

Your boiler pressure should be set between 1 and 2 Bars. If your gauge is set at the ideal pressure, it may be indicated in green on the gauge itself. If your boiler pressure is too high or too low, it could be sitting in a red zone.

For combi boilers, you may see that the pressure gauge is sat towards the lower end of the green zone when the boiler is cool – this is normal.

Alternatively, you’ll see that the pressure dial increases within the green zone when the boiler is heated – again, this is totally normal. As long as the gauge is sat in the green zone, between 1 and 2 Bars, your boiler pressure is set correctly.

Is your boiler pressure too low?

If your pressure gauge is below 1 Bar, your water pressure is too low. Thankfully, this isn’t dangerous. But it can cause the following problems:

  • You don’t have any heating or hot water
  • Your radiators aren’t warming up
  • The pressure dial is below 1 Bar

If this is the case, then you’ll need to increase your boiler pressure.

How increase boiler pressure

  1. Turn your boiler off.
  2. Find the external filling loop – you can find this underneath your boiler. The filling loop is a short length of braided hose that links two water pipes together. There should be levers at each end.
  3. If your boiler doesn’t have a filling loop, it may have a keyed filling loop or keyless internal filling loop. If this is the case, read your boiler instruction manual for more information.
  4. Turn both levers on either end of the filling loop until they are both aligned in the direction of the braided hose. Your boiler pressure gauge should increase and water should start running.
  5. Once the pressure dial hits 1.2 Bar, shut off both valves.
  6. If you can’t see any leaks and the pressure stays up, turn the boiler back on.
  7. Once the boiler has heated and cooled again, check that the pressure is still between 1 and 2 Bars.

Is your boiler pressure too high?

If your pressure dial is sat above 2 Bar, or your central heating system has shut down completely, your boiler pressure is too high.

If the boiler pressure is above 3 Bar, this could be why:

  • There could be too much water in the system
  • The filling loop valves may not be closed properly, which lets water into the system

Thankfully, this isn’t dangerous as your heating system is protected by the boiler pressure relief valve, which is a safety device that lets pressurised fluid leave the system safely.

How to decrease boiler pressure:

  1. Turn your boiler off.
  2. Make sure that the filling loop valves are completely closed. If you’re unsure where to find the filling loop, read step 2 above.
  3. Wait for the heating system to cool.
  4. Next, bleed your radiators to release pressure. Read how to bleed a radiator here.
  5. Once you’ve bled your radiators, check the pressure gauge. If it’s still above 2 Bar, re-bleed your radiators.
  6. Keep doing this until the pressure gauge sits at 1.2 Bar.
  7. If the boiler pressure becomes too low, follow the instructions for low boiler pressure above.

How Swale Heating can help

If you’ve followed these steps and your pressure gauge still isn’t sitting between 1 and 2 Bar, it may be time to contact a professional.

Thankfully, all of our engineers at Swale Heating are Gas Safe registered and can repressurise your boiler. What’s more, if there are any underlying issues, they’ll be able to find this out in a safe and timely manner.

Rely on us to keep you warm.