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Guide

Unvented Hot Water Cylinders in Petersfield: Servicing, Repairs and Replacement

An unvented cylinder stores hot water at mains pressure, so it has safety parts that need looking after. Here is how to tell if you have one, what to ask when booking a service or repair, and what to weigh up if it needs replacing.

If your hot water comes from a cylinder fed at mains pressure with no cold water tank in the loft, it is probably unvented. Book a service with an engineer who works on unvented cylinders, ask what the service checks and what you will get in writing, and do not adjust or take apart its safety valves yourself. For a fault or a replacement, get a written quote that names the cylinder and what is included.

Petersfield.co Editorial17 October 2026

Is your cylinder unvented?

An unvented cylinder is fed straight from the mains, so it usually gives strong hot water pressure and there is no cold water storage tank in the loft feeding it. A vented cylinder is fed from a tank above it. The label on the cylinder normally says which it is; take a photo of it before you ring anyone.

Why it needs looking after

Because an unvented cylinder holds hot water under pressure, it has safety parts such as valves and an expansion vessel. Building regulations guidance on hot water safety is in Approved Document G. Check the manufacturer's manual and guarantee for its servicing terms, and leave the safety valves to a qualified engineer. This guide does not cover do-it-yourself work.

Have this ready before you call

  • A photo of the cylinder's data label: make, model and size.
  • The date of the last service and any paperwork.
  • What you have noticed: no hot water, water dripping from a pipe near the cylinder, noises, or pressure changes.
  • Whether the cylinder is heated by a boiler, an immersion heater or a heat pump.

Questions to ask when booking

  • Do you work on unvented cylinders, and on my make?
  • What does a service check, and what will I get in writing afterwards?
  • If you find a fault, will you quote before doing the repair?
  • Do you cover my address, and is there a call-out charge?

If it needs replacing

Ask for a written quote that names the new cylinder, its size, what is removed, any changes to pipework or controls, the guarantee and what servicing that guarantee requires. If your boiler is also old, our boiler replacement guide covers what to weigh up. For heat pump systems, see booking a heat pump service.

Comparing engineers

Our heating engineer checklist has more questions, and the plumbers and heating category lists local firms.

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Frequently asked questions

How do I know if my hot water cylinder is unvented?
An unvented cylinder is fed directly from the mains and there is usually no cold water tank in the loft feeding it. The label on the cylinder normally says which type it is.
Does an unvented cylinder need servicing?
Check the manufacturer's manual and guarantee, which may set servicing terms. Book an engineer who works on unvented cylinders and ask what the service checks.
Water is dripping from a pipe near my cylinder. What should I do?
Note what you can see, do not adjust the safety valves yourself, and call an engineer who works on unvented cylinders to look at it.
What should a cylinder replacement quote include?
The new cylinder's make, model and size, what is removed, any pipework or control changes, the guarantee and its servicing terms.