If your combi boiler or Vented hot cylinder did not keep it up your hot water demand think about it unvented hot water cylinder. The unvented hot water cylinder gave you 3 bar constant pressure. Gas Safe registered engineer will carry out any repairs as quickly and efficiently as possible at a reasonable price. Your boiler may be the single most important item in your home, particularly around winter, so when it comes to maintaining your boiler or boiler replacement, it's essential to make sure you get it right.