Ive had the boiler for about ten years now and its been reliable apart from the main (large) diaphragm in the two way valve, this is in the service kit and I have to replace it about three times a year because it simply rots and splits causing the central heating and the hot water systems to flow into each other. The system is filled with Tower XXX inhibitor and was mixed to the correct ratio. The entire system was flushed and cleaned about four years ago. The boiler lives in a cupboard in an upstairs bedroom and is protected from damp and cold etc. The central heating and the hot water are never run at maximum heat, I keep them at about 75% (an old habit from a past occupation) in the winter. The Central heating being isolated in summer. There is no sign of debris in the water when I drain it and the gauze filters are also free of debris. Although we live in a hard water area, there are no signs of this inside the boiler. I only ever fit geniune Vokera spares. The gas side of the boiler is serviced by a registered gas engineer and this is up to date.

Shane, September 2007

The diaphram you refer to moves the fulcrum arm when there is hot water demand, doesnt it?. If this is the one, it has incoming cold water from the supply main on both sides. Next time you replace it clean all traces of adhered rubber from the nylon pin pusher plate and from the brass insides that it comes into contact with. You will find it lasts for very much longer, maybe a couple of years or more, depending on useage. They last no time at all if the old stuck on diaphragm bits are not cleaned away.

If the cold inlet and circulating hot water became connected then the pressure in the system (front panel pressure guage) would go right up to your cold water supply pressure, if over 3 bar this would lift the overpressure valve. It would be very unhealthy for your boiler.

c, September 2007