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I have a boiler central heating system in which the central heating and hot water feed off one tank in the roof . I have been advised by a plumber that I need to replace the boiler for a combi system, as the system I have is illegal. Can you confirm and a

Firstly, the type of cylinder you describe (known as a Primatic cylinder - where CH and hot water are separated by an air bubble) is NOT illegal. If correctly set up these can give very satisfactory service - but there can be complications if pumped systems are used.

There appear to be problems with the overall system, but it is difficult to do any "remote" diagnosis. The radiator problem may be "fixable" by bleeding air from the system or perhaps by cleaning and flushing radiators if these are blocked with sludge. However there may be other underlying causes which have resulted in the heating engineer suggesting replacement of the whole system (except radiators I assume).

If the system IS to be replaced then it is not "compulsory" to fit a combi boiler (where the hot water is heated on-demand directly from the mains supply).

While a combi may be convenient (no storage tanks needed), a conventional system with a boiler and storage cylinder can be used - especially if the hot water demand is likely to be high. This can be an open vented system (header tanks in loft) or a sealed system (hot water is stored in a cylinder at mains pressure, with no loft tanks).

You may wish to seek a second opinion from another installer on the best type of system - please ensure that if you do decide to replace the system then any gas work is carried out by a Gas-Safe registered installer.

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