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Boiler Maintenance Advice

What To Do If My Boiler Keeps Losing Pressure

The pressure on your boiler can go up or down for different reasons. Whether you have high or low boiler pressure, we explain how to adjust it and what to do if your boiler keeps losing pressure.

What should the water pressure be when my boiler is not working?

When your boiler is not working, the pressure gauge should be set at about 1.5 bar. On the pressure gauge on the front of your boiler, the needle will be in the centre of the green triangle on the dial. If the needle is below 1 bar, in the red area, the pressure is too low. Your boiler may not work and it will display an error code. You will need to top up the pressure. We explain how below. 

What should the water pressure be when my boiler is working?

When your boiler is heating up your hot water or radiators, the needle will go up a little, but should not go higher than about 2.5 bar. The needle should stay in the green section. If it is too high, a safety valve is fitted that will discharge water to keep the pressure at a safe level. You may need to bleed your radiators to reduce the pressure in the system. We show you how to bleed your radiators here.

Why is my boiler pressure high?

If your boiler pressure is too high, it could be because a radiator has been removed, for example, while decorating a room, and the system was over-filled when it was replaced. If the water pressure continues to be high after bleeding the radiators, please call your heating engineer, or Baxi Customer Support to check the system is safe to use.

How can I reduce the pressure in my boiler?

The best way to reduce the pressure in your boiler is to bleed the radiators. Before you start, make sure your central heating system is switched off. You'll need the radiators to be cool enough to handle. Some modern radiators can be bled with a screwdriver. However, for most types of radiator, you'll need to use a radiator key.

  1. Attach the radiator key into the square section in the centre of the radiator valve
  2. Use a cloth or strong tissue paper to hold the radiator key
  3. Have another cloth under the radiator valve to catch any drips
  4. Turn the radiator key slowly in an anti-clockwise direction
  5. Allow water to leak out of the valve until the pressure gauge on the boiler returns to 1.5 bar.
  6. Close the valve quickly by turning the radiator key
  7. Check the pressure gauge on your boiler. If it’s too low you'll need to top up the pressure again. We show you how here.

Why is my boiler pressure low?

Here are several reasons why the pressure in your boiler is too low.   

  1. Over time, it is quite normal for air to get into the system. You can tell if this has happened because you can feel cold spots on your radiators. Try bleeding the radiators, then topping up the pressure on the boiler (see how to do this below).
  2. There’s a leak somewhere in the central heating system. Check pipes, radiators and radiator valves for signs of a leak, such as rust, corrosion or staining. You may not notice any water, because it may evaporate due to the heat of the pipework before it has the chance to drip.
  3. The expansion vessel inside your boiler may need recharging or replacing. This is a job for a qualified, Gas Safe registered heating engineer. 
  4. There could be debris inside the pressure relief valve.  This is the safety valve that usually discharges water if the pressure in the system gets too high. If it is dripping with water and the pressure gauge is too low, your Gas Safe registered engineer will need to clean out or replace the safety valve.

How can I top up the pressure on my boiler?

It is quite simple to top up the pressure in your boiler. You should be able to do it yourself without having to call a heating engineer. We have made some videos to help you. Please watch the video right to the end before attempting to top up your boiler pressure. If you prefer not to do this yourself, or can’t manage, your Gas Safe registered engineer or Baxi Customer Support will be pleased to help, although you will have to pay.

My boiler keeps losing pressure. What should I do?

It is quite normal to need to top up your boiler pressure once or twice a year. However, if your boiler keeps losing pressure, call your local Baxi Gas Safe registered installer or Baxi Customer Support who will come and check your boiler and system.

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