To adjust pressure in a sealed hydronic hot water heating system, switch it off, let it cool and compare the gauge with the manufacturer’s specified cold-pressure range. This sealed heating circuit is different from normal household mains water pressure. Use only the designated filling valve to increase pressure. To reduce pressure, follow the manufacturer-approved radiator bleeding procedure, if permitted. These steps do not apply to pressure at taps or showers. If the controls are unclear, the system is hot or water is leaking or discharging, stop and contact a licensed professional.
Check the pressure when the system is cold
Pressure rises as the water heats and expands, so assess it only when the system is off and cold.
- Confirm it is a sealed hydronic circuit serving radiators or underfloor heating. Do not use these instructions for an open-vented system.
- Identify the pressure gauge and filling controls from the system manual.
- Check for dripping valves, wet pipework or water beneath the equipment. Do not keep topping up a visibly leaking system.
- Use the recommended system pressure stated in the manufacturer’s manual or marked on the appliance. There is no universal correct pressure.
- Do not operate an unfamiliar valve.
Increase heating system pressure
- Switch the heating off, let it cool and check for visible leaks.
- Identify the designated heating system filling valve or filling loop from the manual. Do not improvise a connection or alter a backflow-prevention device.
- Open the specified control slowly while watching the gauge.
- Stop at the manufacturer’s cold-pressure range, then fully close all filling controls.
Never leave a filling valve open or exceed the specified range.
Reduce heating system pressure
First confirm that the system is cold and every filling control is fully closed. If the manual permits you to bleed a radiator to reduce pressure, follow its procedure and release only a small amount while monitoring the gauge.
Pressurised water and metal components can cause scalds. Stop if the water is hot, sprays, cannot be controlled or the valve is unfamiliar. Do not drain the system or operate, adjust or cap a pressure-relief valve.
Close the bleed valve when the gauge reaches the specified cold range. After either adjustment, confirm all controls are closed, run the heating normally and recheck the gauge once the system has cooled again.
When to call a professional
Stop adjusting the system if:
- pressure repeatedly falls or rises
- a leak or relief-pipe discharge is visible
- pressure rises substantially during heating
- the gauge does not respond normally
- you cannot confidently identify the correct controls.
Do not remove equipment covers or attempt repairs to the boiler, expansion vessel, pump, sealed pipework or safety devices. These faults require assessment by a suitably licensed professional. Check which licensed trade can repair central heating in NSW for the affected component, then contact our licensed hot water repair team to inspect recurring pressure problems and determine the appropriate repair.