DIY How To

Sealed Central Heating System

A sealed system is fed directly from the mains using a flexible filling line. Non return valves (check valves) must be incorporated into the system, to prevent any contaminated water getting back into the mains. A pressure vessel is used to allow the expansion and contraction of the water, as it heats up and cools down. Safety relief valves must be built into the system to relieve excessive pressure and water in the event of overheating.

Sealed system

Advantages of a sealed system are no expansion tank in the loft so it's an ideal system for apartments. Due to the system being pressurised there is less chance of air in the system, which means less corrosion and because the system runs hotter, smaller radiators can be used.

  • Disadvantages are because the system is pressurised, more expensive valves and connections are needed to prevent leaks, radiators get very hot, so extra care is needed especially with children.

Sealed System with Filling Loop

Sealed system with filling loop 1. Boiler
2. Safety valve (see note)
3. Pressure gauge (see note)
4. Expansion vessel (see note)
5. Air release point
6. Hot water expansion vessel
7. Hot water safety valve
8. Unvented hot water cylinder
9. Pump
10. Pump
11. Filling loop with check valves
Note - Sometimes within boiler

 

Sealed System with Make-up Tank

Sealed system with make-up tank 1. Boiler
2. Safety valve (see note)
3. Pressure gauge (see note)
4. Expansion vessel (see note)
5. Air release point
6. Hot water expansion vessel
7. Hot water safety valve
8. Unvented hot water cylinder
9. Pump
10. Pump
11. Filling loop with check valves
12. Non-return valve
13. Make-up tank
Note - Sometimes within boiler
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