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Unvented Hot Water Storage System

Exam revision materials for Plumbing Level 2&3 and ACS Gas Safety test

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Unvented Cylinders

Service and Maintenance

Safety Checks

Expansion Valve Discharge

  1. Manually reset/seat expansion valve
  2. Check pressure downstream of pressure control valve
  3. Correctly size expansion vessel and relief valve
  4. Are boiler and cylinder thermostat cutting off at recommended temperature?
  5. Check charge of pressure in expansion vessel. Does pressure hold?
  6. Exchange expansion vessel
  7. Exchange expansion valve

TPRV Discharge

  1. Manually reset/seat TPRV
  2. Check its temperature is set between 90°C and 95°C
  3. Check energy cut-out device on cylinder
  4. Is motorised valve feeding cylonder operating correctly?
  5. Check operating cylinder thermostat setting/operation is correct
  6. Exchange temperature relief valve
< Go Back2014-04-19

Preliminary Checks

  1. all components are approved for the vessel and are functional
  2. all valves are in the correct operation position and all thermostats are properly wired
  3. evidence of recent discharge and ask the owner if they have noticed any
  4. Temperature Relief Valve is re-seals (can be not resettable and a replacement might be required)
  5. manually check that Expansion Relief Valve re-seals
  6. check for obstruction of the discharge pipe and termination point
  7. check D1 and D2 comply with the Building Regulations
  8. cylinder's Operating Thermostat setting is 60-65°C
  9. isolate gas, water and electrical supplies open at least one hot tap to release the pressure
    1. check, clean or replace the Line Strainer Filter
    2. check the Expansion Vessel pressure
    3. check the Expansion Vessel diaphragm
    4. reinstate the air gap in line with a manufacture instructions
  10. reinstate water, electricity and gas supply and run the system
    1. check that the relief valves are not discharging
    2. check incoming mains water pressure and flow rate upstream of the Pressure Reducing Valve
    3. check the pressure, flow and temperature (min 55°C) at the tap (furthest away) and compare against mains
  11. complete any maintenance records and Benchmark forms

Deteriorating Flow from Taps

  1. Check incoming mains pressure
  2. Check line strainer
  3. Check pressure control valve
  4. Check system for blockage
< Go Back2014-04-19