Plumbing 5 min read8 June 2026
An unvented cylinder runs at mains pressure, so hot water arrives with the same force as cold. For larger homes with more than one bathroom, it is often the best answer.
How it works
Instead of being fed by a loft tank under gravity, the cylinder is fed directly from the mains and sealed, with an expansion vessel and safety devices handling the pressure changes as water heats. You gain loft space and lose the cold tank entirely.
Sizing it correctly
Size is driven by the number of bathrooms and simultaneous demand, not by house size alone. An undersized cylinder means running out mid-shower; an oversized one wastes standing heat. We calculate from real usage patterns.
Annual servicing is not optional
Unvented cylinders contain stored energy and must be serviced annually by a qualified engineer — expansion vessel charge, temperature and pressure relief valve, tundish and controls all get checked. Skipping it invalidates most warranties.
Need help with this?
We handle this work every week. See Plumbing Services in Glasgow or browse all our services.
Frequently asked questions
Do I need good mains pressure?
Yes — we measure flow and pressure at survey to confirm suitability.
Can I keep my existing boiler?
Often yes, if it is a system or regular boiler with adequate output.
Who can service an unvented cylinder?
Only an engineer holding the relevant unvented qualification, which our team does.
Related reading
Combi vs System Boiler: Which Suits Your Home
Bathroom Installation: Planning It Properly
Heating Works But No Hot Water: What's Wrong