Unvented cylinder repairs, servicing & replacement
LDM Group provides fault finding, servicing, repair and replacement support for unvented hot-water cylinders across Surrey, Hampshire and Berkshire. We can investigate pressure problems, tundish discharge, valves, controls, expansion issues and hot-water faults before deciding whether repair or replacement is the right route.
Unvented cylinder problems we can investigate
Unvented systems use mains pressure and dedicated safety controls. A fault can come from the cylinder itself, the inlet-control group, expansion arrangement, thermostats, immersion heaters, valves, controls or the heat source, so proper diagnosis matters.
Tundish dripping or running
Repeated or continuous discharge through the tundish can point to pressure, expansion or safety-valve issues and should be investigated rather than blocked or capped.
Low hot-water pressure
Poor flow may involve the incoming mains supply, strainers, pressure-reducing components, valves or restrictions elsewhere in the system.
Expansion problems
Loss of expansion capacity can lead to pressure rise and discharge. The correct repair depends on the cylinder design and expansion arrangement.
No hot water
The issue may be with the immersion heater, thermostat, controls, boiler or another part of the heating circuit rather than the cylinder vessel itself.
Valve and control faults
Inlet-control groups, motorised valves and temperature or pressure controls can all affect how an unvented system operates.
Cylinder replacement
Replacement may be appropriate where the vessel has failed, parts are obsolete, the cylinder is poorly sized or the existing installation is no longer suitable.
Unvented cylinders need the safety controls treated properly
Unlike a conventional open-vented cylinder, an unvented cylinder stores hot water under mains pressure. The pressure and temperature safety devices, expansion arrangement, tundish and discharge pipework form part of the safety system and should not be altered casually.
Servicing requirements vary by manufacturer and installation, but periodic checks can help identify discharge, pressure and safety-component problems before they become larger faults.
Important: never cap, isolate or obstruct a tundish or safety discharge pipe to stop a leak. Work on unvented safety controls must only be carried out within the required competent scope.
Choosing a replacement unvented cylinder
A replacement should be selected around the property, not just the size of the old cylinder. Hot-water demand, available mains flow and pressure, heat source, recovery time, access and discharge requirements all need to be considered.
Capacity
The cylinder should suit the number of occupants, bathrooms and normal hot-water use.
Mains supply
Unvented performance depends heavily on the available incoming mains flow and pressure.
Heat source
Boiler, immersion and heat-pump systems have different coil, control and recovery requirements.
Discharge route
The safety discharge arrangement must be suitable for the cylinder and property, particularly where access or pipe routes are restricted.
Access and removal
Cupboards, lofts and plant spaces can affect cylinder dimensions, removal and installation planning.
Controls and valves
Existing controls and associated components should be assessed rather than automatically assumed suitable for the replacement.
Unvented cylinder work across Surrey, Hampshire and Berkshire
We cover Farnborough, Frimley, Camberley, Aldershot, Fleet, Farnham, Sandhurst, Bracknell and surrounding areas. Availability depends on the job, location and scope required.
Other hot-water and plumbing services
Unvented cylinder FAQs
Why is water dripping through my tundish?
Continuous or repeated discharge can be caused by expansion, pressure-control or safety-valve issues. The discharge should be investigated and the tundish or outlet must not be capped.
Do unvented cylinders need servicing?
Manufacturers commonly specify periodic checks of safety and control components. The exact servicing requirements depend on the cylinder and installation.
Can an unvented cylinder cause low hot-water pressure?
It can be part of the problem, but incoming mains pressure and flow, valves, strainers and pipe restrictions can produce similar symptoms. Diagnosis should consider the whole supply.
Does a leaking unvented cylinder always need replacing?
No. A leaking valve or fitting may be repairable. If the cylinder vessel itself has failed, replacement is normally required.
Can an unvented cylinder work with a heat pump?
Yes, but the cylinder must be suitable for the heat-pump system and the coil, controls and recovery requirements need to be considered. See our heat-pump cylinder page for more detail.
Need plumbing, heating, gas or renewables help?
Tell us what you need help with and we’ll get back to you after reviewing the details. For urgent plumbing or heating problems, calling is usually the fastest option.
Send an enquiry
Use the form below and include as much detail as possible.
Need help with an unvented cylinder?
Send the cylinder make and model if visible, a description of the fault and photos of the cylinder, tundish, controls and nearby pipework where safe to do so. That can help us understand the system before attendance.