interesting to read your query. We have just had exactly the same problem and were charged £50 cash from a plumber on his way home who was here 15 minutes. on finding it was a thin rubber valve I was trying to locate price of part and came across your question! Hope you have not been ripped off too as I work out that rate is £150 per hour in your spare time!! At least next time we can say we know what the problem is and ask for a quote first!!
sara wilson
April 2008
the diaghramgs in the diverter valve burst quite frequently , thus getting no hot water . When you try to buy a new diaghragm you are told you need to buy the complete diverter valve ( about £100 ) TOSH !!!!
You can buy 5 diaghragms for £5 plus postage online from "boiler Spares "