Unvented Heatrae Sadia cylinder discharges water regularly from the tundish during heating.

Safety first: Components on unvented cylinders operate under high pressure and temperature. Work must comply with local regulations (e.g. G3 in the UK). If unsure, contact a qualified engineer.

Steps to investigate:

• 1. Observe discharge pattern: Occasional drips during heat-up can be normal. Continuous flow or heavy discharge is not.
• 2. Check pressure gauge: If fitted, note cold and hot pressures. Excessive rise suggests expansion vessel issues.
• 3. Test expansion vessel: Isolate and drain pressure from the cylinder side, then measure the vessel air charge with a tyre gauge. Recharge to the manufacturer’s specified pressure using a pump, or replace the vessel if the diaphragm has failed.
• 4. Inspect pressure reducing valve (PRV set): Ensure the inlet PRV is not blocked and is set to the correct pressure. Replace if faulty.
• 5. Check pressure relief valve: Briefly operate the manual test lever to flush debris from the seat. If the valve continues to pass water, replace it with the correct Heatrae Sadia safety valve assembly.