Topping Up Your Boiler


Topping Up Your Boiler

Note: Not all boilers require “topping up”. If in doubt, ask us.

When to top up…

  • Pressure gauge reading zero bar
  • Boiler displaying a low pressure fault code, or possibly overheating
  • Everytime you bleed radiators
  • When you bleed upstairs radiators and no water or air comes out
  • Rushing water noises in your system
  • Everytime a heating system is drained (Additional steps should be taken)
  • You should check your system pressure every 6 months

Types of system that will need topping up…

  • If you have a “sealed” heating system
  • If you have a combination boiler
  • If you have no tanks in your loftspace or at high level
  • If you only have a single large tank in your loftspace or at high level for hot water

How to topup your system…

First of all you should be comfortable undertaking very basic tasks in the home like putting pictures up and levelling shelves, you should also be comfortable with the operation of your boiler; if you are not, then contact the professionals like us first and we’ll happily send someone out to walk you through it.

As with all things DIY and boiler related, do it wrong and it could cost you in a pricey repair bill.

Now, there are a couple of components that you will need to identify before you begin. You will need to identify:

  • Current system pressure, this will usually be in the form of a pressure gauge
  • The method of filling the system

Current system pressure…

The system should, when cold be between 1bar and 1.5bar. This will be indicated in one of two ways; via a pressure gauge or via a digital display on the boiler itself… In some cases, your boiler will require a button press to enable the pressure display, but most installers will fit a secondary gauge, just in case the pressure sensor in the boiler becomes faulty.

Pressure Gauges

The gauge will normally look a little bit like those pictured above, however there is a large variety available, what you need to identify on the gauge is the current pressure in BAR. Some gauges will have 2 arms, a red and a black, in the majority of cases, the red arm is used to indicate where the pressure “should” be, however it can often be adjusted by simply turning the glass screen or using a screwdriver to operate the centre point of the arm. However, the black needle will normally be the needle we are interested in; this should (With the boiler “off” be indicating a pressure between 1 and 1.5 bar. If it’s lower, then you will need to continue reading. If it’s higher, then you should not add any more pressure (See below for dealing with excessive pressures).

Method of filling the system…

These too, like the gauges will vary widely and can be literally “anywhere” in your home. There will often be a “filling loop” fitted to your system or, your boiler may have an integrated filling device located underneath where all of the pipework connects. Integrated filling devices are more commonly found on combination boilers and are extremely rare on boilers that have hot water cylinders.

Filling Loops Filling Loops

The loop is made up of one or two valves and a braided hose. The braided hose may or may not be connected as current regulations state that the braided hose should be disconnected when not in use. If it’s not connected, you’ll need to connect it between the cold mains filling point and the heating filling point, do not overtighten it, a little drip from a filling loop when filling is quite normal.

Once located and connected, you’re ready to fill. However, if you’ve not yet found your filling loop and you have a combination boiler (Especially an older Vaillant or Worcester Bosch as we find these often catch people out) then you may need to consult the manufacturer’s manual for further information.

The filling process…

Depending on the type of loop, you may need a flat bladed screwdriver to operate the valves. There will often be two valves that need operating and hopefully you’ll have little lever’s that you can use. But if you don’t, then get that screwdriver out as the process is the same.

Filling Valves

From the picture above, you’ll see when looking “top-down” to the one or two valves either a thumb tap or a slot for your screwdriver blade…

OFF is when the lever or slot is “against” the pipe… As pictured in green.
ON is when the lever or slot is “in-line” with the pipe… As pictured in blue.

Make sure that you understand on and off before you begin; it’s now time to turn your heating and hot water off, including your boiler if it has a power switch. Now; the steps are simple. If you have a two valve or two lever filling loop, open one valve with the other one left closed.

  • With the closed valve, slowly begin to open it whilst keeping an eye on that pressure gauge. You’ll hear a lot of rushing water noises and you may get a bit of a drip from the loop.
  • The pressure will slowly start to rise, don’t rush; but if you can control the rise, you can open the valve up a little more.
  • When the pressure starts to reach 1.25Bar, begin closing the valve.
  • Close the valve and the pressure should stabilise, make any minor adjustments as needed until the pressure sits comfortably between 1 and 1.5Bar.

If you have a two valve or two lever loop, close the second valve. You can all then remove the filling loop and put it back to where you found it. Some boilers are designed to have their loop left connected, if in doubt, read the manual or contact one of our engineers for advice.

If you over-pressurise…

Oh dear… Pressure gone above 1.5Bar when everything is off and cold? Don’t panic. You’ll normally get away with upto 2Bar and sometimes even more; but it’s just not needed. However, if you managed to hit the 3Bar mark, you should remove some pressure. Likewise; if when the boiler fires, the pressure raises to the 3Bar mark, you may have too much pressure (If the pressure rises rapidly, you have a fault, contact us for an appointment).

To remove pressure takes a little extra skill, some hoses and can cause leaks. The easiest method we suggest is by turning everything off, put a piece of hose on your systems drain point and open it gently. When the pressure is acceptable, close the drain off. However, due to the complexities of removing pressure, we’ll go through this another day – Stay tuned.