Bosch W275 water heater, diaphragm leaking?

Just had the diaphragm rubber replaced in my W275 boiler this weekend as it had perished. I watched the plumber so can help a bit. There are several different types of diaphragm (apparently) so get the exact boiler model number (on the data plate) and check. The problem might be the diaphragm rubber itself - although that looked pretty much enclosed - but might actually be the 'valve' at the bottom - there is a pin running through this that is pushed by the internal diaphragm and actuates the external microswitch - this 'valve' has obviously got to be watertight, might it be that that is leaking? If it is the diaphragm rubber/housing then you'll probably have water running down the outside of the body of the main control assembly? The diaphragm rubber is in the circular section approx 2.5" diameter about 3" up from the microswitch. To remove, switch gas and water off, remove batteries, drain water. Pull off water temp knob then unscrew and remove the circular surround. Boiler cover then lifts forward and up to remove. The water inlet pipe is secured by an inverted 'U' shaped pin pushed through the housing - remove this and the inlet pipe pulls free. Gas pipe is secured with an obvious nut - undo with a wrench. There are then three (four?) screws holding the diaphragm valve assembly on - didn't see exactly where they are but you should be able to work it out. The bottom section of the control assembly then comes free. Another four (five?) screws to separate the two halves of the diaphragm housing, this comes apart and diaghragm rubber can be replaced. *** YOU'VE GOT TO DISCONNECT AND RECONNECT THE GAS - ENSURE YOU KNOW WHAT YOU'RE DOING! *** Look on the Bosch/Worcester website and there is an install manual for the W275 with an annotated diagram.

S
July 2011