Boiler System Pressure

On sealed systems such as combination boilers or ones where the system has an expansion vessel(usually red), guage and filling loop, making sure the pressure is set correctly and remains stable during normal operation. Following are the guidelines for typical houses or flats.

1. Initial pressure is ideally set at 1.2 bar. Routinely many engineers set at between 1 and 2 bar. The exact pressure is dependent on the design of the system and how low/high the boiler is positioned in the house and how many floors their are. As stated for the average house 1.2 bar is ok.

2. During operation of boiler, ie when heating comes on and off, the maximum recommended pressure rise should be 0.5 bar. For example if you fill to 1 bar, then the max it should rise to is 1.5 as long as the expansion vessel is correctly sized and all other components are working correctly.

3. The max a heating system will tolerate is 2.5 – 3 bar before water starts escaping from the pressure relief valve.

Signs of Problems:

1. If the pressure rises during operation higher than 0.5 bar from initial fill, then could be signs of incorrect expansion vessel sizing, or if it continues rising past 2.5, then the expansion vessel may need to be refilled (0.75bar on average systems) or replaced.

2. If the pressure keeps dropping, either the pressure relief valve has debris stuck on the washer, allowing water to escape or you have a leak on the heating system.

Long Term Problems:

1. Continual topping up of the system will cause corrosion by means of inhibitor being diluted or new minerals being introduced to the system. Better to fix the small problem before a bigger problem occurs.

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