Testing For A Back Boiler Stove Leak - UNVENTED HEATING SYSTEM

Diagnostic: Testing for Leaks in a Back Boiler on an Unvented System

Unvented heating systems operate under pressure and do not incorporate a header tank, making the diagnosis of leaks more technical and requiring greater attention to safety and compliance. Leaks in an unvented system can pose safety risks and must be managed by appropriately qualified professionals.

How to Check for a Leaking Back Boiler on an Unvented System

1. System Pressurisation and Observation:

   • Ensure the heating system is completely cold before starting any checks.
   • Note the system pressure as displayed on the pressure gauge (typically located on or near the boiler or at the filling loop).
   • Top up the system to the manufacturer’s recommended cold-fill pressure if required (most domestic systems: 1–1.5 bar at cold).
   • Isolate the stove/back boiler circuit, if possible, using system valves.
   • Monitor the pressure: Leave the system unused for several hours, ideally overnight. Any unexplained pressure drop indicates water loss, which could be due to a leak in the back boiler, pipework, or other system components.

2. Visual Inspection:

   • Check for visible signs of water around the stove, joints, and adjacent pipework.
   • Inspect all accessible parts of the system, including beneath floorboards if possible, for evidence of weeping or corrosion.

3. Check for Activation of Safety Devices:

   • On an unvented system, a recurring need to re-pressurise or persistent pressure loss may cause the pressure relief valve (PRV) to discharge water, often via a pipe to the exterior of the property. A continuous trickle or damp patch beneath the PRV discharge point suggests ongoing water loss elsewhere in the system.

4. Confirm Leak Location:

   • If the pressure continues to drop but no leak is immediately visible, isolate zones within the system if possible to identify whether the issue lies within the back boiler circuit.
   • If the back boiler circuit is isolated and the pressure stabilises, the leak is likely in that section.

Important:

• Safety First: Unvented systems operate at higher pressures and incorporate safety-critical components (expansion vessel, PRV, temperature and pressure relief valves). Any suspected leak or signs of pressure fluctuations should be assessed by a qualified and certified heating engineer with unvented (G3) certification.
• Do Not Attempt Repairs: Repairs or intrusive testing on unvented systems should only be carried out by professionals due to the potential safety risks involved.

Integrating this approach provides homeowners with a clear, step-by-step process for identifying leaks on unvented systems, while reinforcing the importance of professional intervention to maintain both safety and system performance.