Open-Vented or Sealed Heating System
An open-vented system uses a feed-and-expansion tank in the loft to manage pressure; a sealed system uses an expansion vessel and is pressurised from the mains.
An open-vented system uses a feed-and-expansion tank in the loft to manage pressure; a sealed system uses an expansion vessel and is pressurised from the mains. The choice affects the whole heating circuit, not just the boiler.
The case for staying open-vented
Old or fragile pipework that has never seen sealed pressure, or a loft tank in good working order, can make sealing the system a risk not worth taking without other work.
The case for going sealed
A cleaner installation without loft tanks, more consistent pressure, and compatibility with modern system and combi boilers all favour sealing where the pipework can handle it.
Which wins when
Converting is usually done alongside a boiler change, since it requires pressure-testing the whole circuit. Doing it in isolation on old pipework carries more risk than reward.
What we check before converting
- Condition of existing joints and pipework under test pressure
- Whether the loft tank is being kept for another purpose
- Radiator valve and vent condition throughout the system
Who does the work
- Gas Safe registered engineers — registration 554328
- Worcester Bosch accredited installer
- John The Plumb Ltd, company registration 10026483
Discuss converting your heating system
Tell us about your current loft tanks and pipework age and we'll advise whether conversion makes sense for your house.
Questions we get asked
Is converting to sealed always worth it?
Not automatically — on old, fragile pipework a conversion can expose weak joints that gravity pressure never stressed.
Does a sealed system need annual attention?
Yes, checking system pressure and the expansion vessel charge should be part of any annual service.
Can I convert without changing the boiler?
Technically sometimes, but it's most sensibly done at the same time as a boiler change since both involve draining and pressure-testing the system anyway.