Combi-Boiler lost Pressure

The boiler fitted to a central heating system, will at some point probably suffer loss of system water pressure. Now you will be able to read the pressure gauge which is a great indicator but how has this actually happened and how can it be resolved. Lost pressure can be down to a water leak in a pipe or even a failure in the expansion equipment fitted, resulting in relief valve damage. Hornsey Plumbers are a fully qualified plumbing service. Having constant pressure is important and in most modern combination boilers is kept by the flow of cold water supply through a mechanism known as the ‘filling loop’. The system can be re-pressurise through this loop. Study your boiler’s manual to see whether you can re-pressurise it yourself. Or you could employ a professional like a Hornsey Plumber to do the job.

If you can manually re-pressurise the boiler:

1). Identify the filling loop and the pressure gauge.

2). Ensure that the pressure gauge can be monitored while accessing the filing loop (the ideal pressure for any sealed system is 1.5bar). The filling loop should have a silver flexible tube with two handles, in the off position the handles will be across the flow of the pipe. Slowly turn them so they are in line with the pipe. You should now hear the water moving through into the boiler.

3). Carefully check the pressure gauge as it climbs into the green area or the 1.5 bar marker. Turn the handles back to the original position.


Over pressurising, can happen if you cannot monitor the gauge as you increase its pressure. If you can’t do this yourself, ask someone to help you. If there are still pressure issues when you re-pressurise your boiler. You should seek advice from a professional.

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