Safety Protocol & Classification
Safety Classification: CALL-A-PRO
Homeowner DIY Checks Allowed: NO — Professional Technician Required
What This Symptom Means
A hydronic system is a sealed loop. Persistent pressure loss means fluid is escaping through a leak, a failed relief valve, or a water-logged expansion tank.
Likely Causes
- Failed expansion tank diaphragm (forces thermal expansion out the 30 psi relief valve).
- Weeping pressure-relief valve due to sediment or seat wear.
- Concealed piping leak in floors, walls, or underground slab loops.
- Leaking automatic air vent seals releasing small amounts of fluid continuously.
- Pin-hole leak in primary heat exchanger.
Homeowner Inspection Boundaries
Because this symptom directly involves sealed pressure vessels, gas combustion, high-voltage circuits, or boiler safety limit devices, homeowner DIY disassembly or internal testing is not permitted under Hydronic Authority safety guidelines. Homeowners should observe external indicators (such as display codes or pressure gauges) and contact a certified hydronic technician.
What NOT To Do
- Do not repeatedly open the manual fill valve to repressurize without fixing the leak (introduces oxygen and causes rapid corrosion).
- Do not manually pull or test the pressure relief valve lever (it will fail to reseat and drip continuously).
- Do not add cold makeup water to a hot, dry boiler.
When to Call a Professional
Call a pro if you must top up pressure more than once or twice a season, if water is visible near the relief discharge, or if cold pressure drops below 10 psi repeatedly.
Error Code Cross-Reference
If your boiler display is showing an error code or fault message associated with this symptom, look up the code in the Phillips Hydronics Error Code Library for exact manufacturer actions.
Related Equipment & Component Guides
Sources & Documentation
- hydronic-authority/boiler-losing-pressure.html —
- hydronic-authority/boiler-troubleshooting.html —