North London based · Greater London coverage
Unvented Cylinders London — Install, Service & Replacement
Tell us the cylinder model, symptoms or replacement plans. We will discuss the appropriate specialist scope, available attendance and what needs confirming before work.
Specialist cylinder work is scoped and quoted separately. Attendance does not include diagnosis or repair.
Discuss a Cylinder VisitDiscuss your cylinder enquiry
How an unvented cylinder actually works
Understanding the supply, expansion arrangement, safety controls and heat source helps define the right enquiry. These explanations are for choosing an assessment, not instructions to service a pressurised system yourself.
The cold-water supply
An unvented cylinder is supplied from the mains rather than a loft cistern for its stored hot water. Available performance depends on the incoming supply, controls, pipework and demand. It does not guarantee a particular pressure at every tap.
For a conversion, assess available flow and pressure under relevant conditions, simultaneous use and the selected manufacturer’s requirements. There is no single borough-wide pressure or universal survey threshold used on this page.
Expansion provision
Heated water needs provision for expansion. The arrangement depends on the cylinder: some use a separate expansion vessel, while some Megaflo models use an internal air space. Identify the exact model before applying maintenance instructions.
Discharge during heating needs assessment of the actual system. Do not assume that every drip means a vessel needs recharging, and do not operate safety valves or add pressure as a trial repair.
Safety controls and discharge
Unvented systems rely on appropriate temperature, pressure and discharge arrangements. The tundish provides a visible indication of discharge; it must not be blocked to stop a drip.
An installer must assess the discharge route against the product instructions and applicable Building Regulations. Existing pipework is not automatically suitable for a replacement, particularly where access or a shared building is involved.
The heating source and controls
Direct models normally heat electrically; indirect models receive heat from an external source. Backup and renewable arrangements vary. A working boiler or illuminated timer does not prove that the cylinder is receiving heat.
Report whether all hot outlets are cold, only one outlet is affected or flow itself has stopped. Internal electrical, thermostat and safety-control work requires appropriate competence; keep covers closed.
Vented vs unvented — the head-to-head
Whether conversion is worthwhile depends on the supply, property and hot-water demand. Compare these trade-offs before selecting a replacement.
| Aspect | Vented | Unvented |
|---|---|---|
| Supply arrangement | Normally supplied through a cold-water storage cistern | Mains-fed stored hot water |
| Outlet performance | Depends on available head, pipework and any pump | Depends on incoming supply, controls and simultaneous demand |
| Space and access | Consider cylinder and cistern locations | Consider cylinder, controls, servicing clearance and discharge route |
| Installation requirements | Check applicable requirements for the proposed work | Confirm competent installation and the building-control route |
| Maintenance | Follow equipment and system requirements | Follow the matching manufacturer’s service instructions |
| Freeze protection | Assess vulnerable cisterns and pipework | Mains and other exposed pipework may still require protection |
| Cost comparison | Quote the complete repair or replacement scope | Quote supply, access, controls, discharge and commissioning scope |
| Temperature management | Appropriate storage and outlet controls remain important | A sealed system does not remove temperature or scalding risks |
Sizing guide — capacity for your household
Capacity should follow the household’s demand and the heating arrangement. Use these questions to explain your requirements; a model recommendation needs a property-specific assessment.
| Household | Sizing question | Notes |
|---|---|---|
| Small household, one bathroom | Assess actual demand and recovery | Record shower flow and duration, bath use and the available heating periods rather than choosing by bedroom count alone. |
| Two bathrooms used together | Check simultaneous demand | A larger cylinder does not improve an inadequate incoming water supply. Assess storage and delivery together. |
| Family with successive showers | Model the busiest normal period | Explain who uses water and when. Compare how much is stored with how quickly the intended heat source can recover it. |
| Heat pump or renewable integration | Match the heat-source specification | Ask for the selected cylinder’s compatibility and recovery information; do not assume every indirect model is suitable. |
| Shared house or HMO | Survey peak use and service needs | Agree demand assumptions, access, user controls and any distribution requirements for the specific property. |
| Larger or commercial property | Specialist design and quotation | Storage, recovery, circulation and controls need a defined design brief. No standard residential capacity is promised. |
Comparing cylinder brands and product types
Compare the proposed model and support arrangements, not an unsupported brand ranking.
Megaflo
Identify the range and heat source
Use the full model label to distinguish direct, indirect and other variants. Ask how the selected model suits demand, available space, expansion provision and maintenance access. A brand name alone does not specify the installation.
Range Tribune
Compare the actual proposed model
Request the model’s dimensions, recovery information and installation requirements with the quotation. Compare the complete fitted scope and current warranty conditions rather than assuming all capacities or variants perform alike.
Mixergy
Include controls and connectivity in the decision
Discuss the intended heat source, user controls and support arrangements as well as capacity. Smart controls do not establish a guaranteed percentage saving for a particular household. Match any fault guidance to the controller and product generation.
Gledhill
Distinguish a cylinder from a thermal store
Confirm the product family. A BoilerMate thermal store is not simply an interchangeable unvented cylinder. A replacement proposal should explain the existing arrangement and how hot water and any connected heating will work afterwards.
Other manufacturer or boiler-matched options
Assess compatibility rather than a brand ranking
If a particular cylinder is proposed with an existing boiler or heat pump, ask which compatibility information supports the choice. Compare usable space, demand, heat-source requirements, controls and service support. Ask whether any manufacturer-specific authorisation is relevant to the proposed work.
Cylinder servicing — five points to agree
Follow the manufacturer’s maintenance instructions and agree the service scope with a competent specialist. These points help you understand the proposed visit; they are not a universal service checklist or a fixed-price offer.
Identify the product and service history
The service should follow the matching manufacturer’s instructions. Supply the label, installation record and previous findings so model-specific requirements can be checked.
Assess expansion and safety functions
A competent specialist checks the installed expansion arrangement and relevant safety controls. These are professional service tasks, not instructions for a homeowner to operate or adjust valves.
Inspect discharge and visible condition
Discuss any tundish discharge, corrosion, leaks or changes in performance. The inspection should consider the intended discharge route and accessible components, with further work identified separately.
Check the heating and control arrangement
Report differences between scheduled heat, boost and normal hot-water use. Electrical and heat-source checks must be undertaken by appropriately qualified personnel within the agreed scope.
Keep the service and completion record
Retain the findings, work completed and any further recommendation. Check the manufacturer’s actual warranty and maintenance conditions; this page does not promise universal warranty or insurance acceptance.
Illustrative cylinder planning situations
These examples explain decisions a survey may need to address. They are illustrative, not completed AK projects or customer testimonials.
Illustrative conversion: a home with a loft cistern
A household wants to replace its vented arrangement. The assessment needs incoming supply measurements, peak demand, cylinder location and a viable discharge route. A proposal should identify any pipework or electrical changes before a replacement is selected. This is a planning example, not an AK job record.
Illustrative flat: restricted access and shared services
A resident needs hot water restored but the cylinder cupboard and discharge route involve shared areas. The enquiry should identify the model, current fault and who can authorise access. Investigation, replacement and making good should be distinguished in the quote. No price or completion time is implied.
Illustrative replacement: a narrow cupboard
A smaller diameter alone does not prove that a cylinder will fit. Check height, connection positions, removal route and service clearance. The proposal should explain the selected model and any required alterations rather than relying on the nominal capacity of the old unit.
Confirm competence and completion documents
Before authorising specialist work, confirm the proposed installer’s competence, relevant registration where applicable, and the building-control route. Ask what commissioning and service records you will receive. Qualification, scheme membership, manufacturer approval and insurance are separate checks. Request the evidence relevant to the proposed work.
Source: Approved Document G for England. For model-specific instructions, use the Heatrae Sadia literature library or Mixergy support hub.
Unvented cylinder enquiries across London
AK is based in North London and covers Greater London. Share your postcode, model and access requirements so availability and the appropriate service scope can be discussed.
Frequently asked questions about unvented cylinders in London
How does an unvented cylinder differ from a vented cylinder?
Who should install an unvented cylinder?
How often should it be serviced?
What size cylinder should I choose?
Can I convert from vented to unvented?
Which brand is best?
What does a cylinder visit cost?
Can an unvented cylinder be fitted above ground floor?
How long will replacement take?
Who handles building-control paperwork?
Related plumbing services
Hot water cylinder replacement
Discuss replacement scope, access and the existing heat source.
Leak investigation
Investigate an uncertain water source before assuming the cylinder is responsible.
Boiler repair
An indirect cylinder may require coordinated assessment of its external heat source.
Plumbing repairs
For accessible plumbing faults and related fittings.
Book your unvented cylinder survey
Tell us the model, symptoms and access details. Engineer attendance is £60, with no VAT added; specialist assessment and work need an agreed scope and quote.
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