How to adjust the water pressure on a gas-fired water boiler

Gas fired water boilers in good condition don’t lose or gain pressure under normal circumstances. After installation household components such as baseboard heaters, radiators or hot water under-floor heaters are filled with water that remains in the system indefinitely. If the pressure gauge on your boiler rises or falls unexpectedly, check for leaks. If you don’t find any, adjust the boiler’s manual water feeder valve.

Check the owner’s manual to determine your boiler’s water pressure settings. This should be somewhere between 1 and 1.5 bars.

Locate the automatic pressure-reducing/water feed valve. This is usually a gold coloured device with a bell-shaped cap located on the inlet side of the pressure chamber feed pipe. You will find a threaded adjustment screw secured with a lock-nut protruding from the top of the valve’s dome.

Insert the tip of a flat-head screwdriver into the slot on top of the threaded adjustment screw. Undo the locknut in an anticlockwise direction with an adjustable spanner.

Turn the adjustment screw clockwise to increase water pressure or anticlockwise to reduce pressure. Make small adjustments and monitor the water pressure gauge while doing so. Tighten the locknut when the gauge displays the recommended pressure.


If pressure starts bleeding off after adjustment, contact your boiler service technician and ask him to check the backflow preventer located on the pipe leading to the pressure reducing/water feed valve. If the backflow preventer is serviceable, the pressure reducing valve is faulty and must be replaced.

Things You'll Need

  • Flat head screwdriver
  • Adjustable spanner
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About the Author

After graduating from the University of the Witwatersrand and qualifying as an aircraft engineer, Ian Kelly joined a Kitchen remodeling company and qualified as a Certified Kitchen Designer (CKD). Kelly then established an organization specializing in home improvement, including repair and maintenance of household appliances, garden equipment and lawn mowers.