Mr. Maurice Buckley:

Normally there is no connection to the mains water coming in. In a traditional system, the mains water comes in and services the tap in the house and then goes to the storage tank and everything else is fed from this. As the petitioner rightly says, in recent years we have gone to the European system where we pressurise the system. Historically, there was a 40 litre expansion tank in the attic with an expansion pipe which was totally separate to the normal storage tank. People have been copying the European system, where the system is pressurised directly using a pressure vessel, pressure release valve and pressure gauge.

Rather than using a pump system or something like that, they use the mains pressure to fill and pressurise the system. I suppose there is nothing wrong with that; it is allowed, but it is temporary. There should be a temporary connection between the central heating system and the mains, with a double-check valve or protection on it when it is connected, along with a shut-off valve. In order for contamination to occur, the two systems would have to be connected, there would have to be a sudden depressurisation in the mains supply, and the double-check valve would have to fail. The problem is that people are leaving the two systems permanently connected, which is not supposed to happen, and, as the petitioner has stated, using a valve that may not be as robust as the type that is recommended.