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Central Heating Boiler Pressure Low

This web page describes the symptoms and fixes for low central heating boiler pressure.


The central heater boiler pressure meter will be on the front of the boiler, see image below.


Central Heating Boiler Pressure Meter


The meter will have an indication of the expected (normal) pressure when cold; the indication in the image above is a red marker (line) on the pressure meter.


The expected pressure will be about 1.2 bar when cold and about 1.5 when hot. The pressure in the central heater boiler above is slightly low.


The boiler will turn itself off at about 0.5 bar.


Symptoms Of Low Central Heating Boiler Pressure

  • Banging noises.
  • Radiators upstairs not working.
  • Radiators furthest away from the boiler not working.
  • Boiler turns itself off.


Fixes For Low Central Heating Boiler Pressure

  • Bleed radiators
  • Look for leaks - usually from pipe joints – under boilers, near radiators.
  • Re-pressurise the central heating by using the 'filling loop'.
    • Usually a small tap or screw - the tap or screw allows more water into the central heating.
    • The filling loop fills the central heating system with water from the mains water.
    • Turn the tap or screw until the pressure is at about 1.2 bar then turn the tap or screw off.
    • The filling loop is not part of the boiler but will be somewhere near the boiler – the filling loop connects by pipes to the boiler.
    • See the image below – the filling loop is marked.

Central Heating Filling Loop


  • If no leaks, or re-pressurising the central heating does not work, the problem is probably the expansion vessel or pressure relief valve.
    • Call a central heating engineer.
    • A 'DIYer' cannot fix an expansion vessel or pressure relief valve problem.


Judge Electrical Limited
15 Mulberry Court, Huntington, York, YO32 9TU
Telephone 01904 764845 (Landline), 07919 033113 Mobile)
Email info@judgeelectrical.co.uk
VAT No. 852917405. Company Number 6359328