How to Fix / Troubleshooting

Safety first: Allow the system to cool before checking pressure or opening vents.

Step 1 – Check expansion tank: With system pressure at zero, measure the expansion tank air charge. Recharge to the correct pressure if low, or replace if the bladder has failed.
Step 2 – Inspect air vents: Look at automatic air vents on or near the boiler for signs of staining or crust indicating slow leaks. Replace if leaking.
Step 3 – Plate heat exchanger test: If system pressure rises when domestic water is used, or drops when domestic side is pressurized, the plate heat exchanger may be leaking internally and should be replaced.
Step 4 – Leak detection: For concealed leaks, a heating professional may need to use leak detection dye or pressure testing to locate the problem.

Warning: Continually topping up the system introduces oxygen, accelerating corrosion. Address pressure loss promptly.

Boiler frequently loses pressure over days or weeks without visible leaks

Possible Causes