If the pressure in your boiler goes down regularly, it is likely that you have a problem with your boiler, or elsewhere in your central heating system. You can re-pressurise it yourself, if you know how, but it’s advisable to get it done professionally if you have no prior experience. Re-pressurising the boiler will get it up and running for you, but if you do this regularly without having the root cause investigated, you could cause irreparable damage to your boiler by introducing scale and allowing other underlying faults to worsen and cause more damage. As well as pressure dropping too low being a problem, pressure rising too high is also a fault that needs repairing. There are various reasons why the pressure in your heating system can fluctuate, so if this is happening, get in touch with a renowned company offering boiler services.

What Is The Right Boiler Pressure?

There is usually a built-in pressure gauge in the boiler or sometimes elsewhere on the pipework, where you can see the pressure displayed. It is normally located within eye shot of your filling loop, so that you can top up the pressure while reading the gauge. Sometimes it is visible as a digital reading on your boiler display. System pressure should ideally be between 1 and 1.5 bar when cold, and a little higher when the heating is warm, but never as high as 3 bar or more.

When Does The Pressure Become High?

The pressure reading increases when the boiler starts heating the water in your radiators and the heated water expands. Typically the pressure will increase from 1-1.5 bar up to perhaps 2-2.8 bar when the heating is on. The exact increase is based on the amount of water in your system, the temperature it is increased by, and the size of any expansion vessels on the system, but as a rule it will always increase when heating up. If your pressure regularly goes above 3 bar or below 1 bar,you need to get in touch with a heating professional as you have a boiler fault.

Why Does The Boiler Pressure Reduce?

The most obvious thing to look for is leaks. These could be drips from the boiler, the central heating pipework or at the radiator valves and radiators themselves. Look out for damp patches on walls and ceilings, or crusty green and white leak marks on pipework.
Water could also be dripping from your boiler safety valve discharge. You can usually check this at a copper pipe coming out of the wall outside, behind the boiler. If this is dripping, you need a boiler repair engineer.

When Does The Pressure Become Low?

If your boiler pressure is below the 1 bar mark, top up the pressure using the filling loop. Call a professional if you are unsure.

How Can Increase The Boiler Pressure?

Make sure you switch off the heating and hot water, and allow the boiler to cool completely before you start re-pressurising it. First, find the filling loop before you start increasing the pressure. You will sometimes find a hose below the boiler, or there may be an internal filling loop on the pipework on the underside of the boiler.

There are quite a few different types of filling loop but in this instance, we will cover the procedure for the universal external filling loop. This looks like a metal braided hose with a valve at either end that you can open by turning a quarter turn with your finger and thumb. Keep the valves open till the pressure increases and close them immediately after it reaches the 1.5 bar mark. Please be aware that this can happen very quickly, so keep your grip on the valves, and your eye on the gauge, so as not to over shoot.

At this point it’s a good idea to vent the radiators throughout your property, and then make sure to top the pressure back up to 1.5 bar.

Though you now know how to temporarily fix the pressure issue in your boiler, it is always advisable to get in touch with experienced professionals and prevent any sort of damage to the heating and boiler.