Strong hot water to several bathrooms at once, from a boiler and cylinder working together.
A system boiler heats your radiators and a stored cylinder of hot water. Unlike a combi, it is not limited to producing hot water on demand, so two or three showers can run together without the flow collapsing. That is why system boilers are the usual choice for larger homes and busy households. Installing one, or replacing an existing one, is really about getting the boiler and cylinder right as a pair.
John The Plumb is Gas Safe registered (554328) and a Worcester Bosch accredited installer. We are G3 qualified and we fit Megaflo, Telford and Joule cylinders, so the boiler and an unvented cylinder can be installed together. A free in-home survey leads to a fixed price in writing, and a magnetic filter is fitted as standard.
A system boiler is worth considering if your home has two or more bathrooms, several people showering in the morning, or a large bath that a combi would take ages to fill. It also suits homes where you would like to keep the option of an immersion heater as backup hot water. Where demand is modest and space is tight, a combi can still be the better answer; our combi vs system comparison sets out the trade-off.
If you already have a system boiler and cylinder, the simplest route is often a like-for-like boiler swap that keeps the cylinder. We check the cylinder's age and condition at the survey. If it is tired, undersized or a vented cylinder you would like to upgrade, replacing it at the same time avoids a second disruption later. The pump, expansion vessel and controls built into a modern system boiler replace older separate components.
An unvented cylinder fed at mains pressure gives the strongest showers and frees the loft of tanks, but needs good mains pressure and flow and a safe discharge route. A vented cylinder fed from a loft tank remains simpler where the supply is weak. Cylinder size is chosen around how much hot water the household uses and how quickly it needs to recover. We test the supply before recommending either.
Many homes with a regular boiler and loft tanks move to a system boiler during a replacement. The feed and expansion tank can come out, the heating circuit is sealed and pressurised, and the cylinder may be changed to unvented. Older pipework and radiators need checking first, because a sealed system runs under pressure. Where that is a concern, we will say so before you commit.
The heating system is cleaned before the new boiler is connected and a magnetic filter is fitted. The boiler is commissioned, the cylinder controls and any zone valves are set up, and the hot water and heating are tested throughout. We explain the programmer and cylinder thermostat at handover and leave the registration paperwork with you.
A combi heats water on demand with no cylinder. A system boiler heats a stored cylinder, so several outlets can run at once. Our combi vs system comparison explains the differences in detail.
Not always. A cylinder in good condition can often stay. We check its age, size and condition during the survey.
Yes, if your mains pressure and flow are adequate. We are G3 qualified and fit Megaflo, Telford and Joule cylinders.
Free survey covering the boiler, cylinder and supply, with a fixed written quote.