Please help with a Vaillant boiler? Turbomax combi 282e?

Hi, My Vaillant turbomax 282e c/h boiler is taking it's time lighting up after you've opened the hot tap. I have mistakenly replaced the flow switch thinking that it was the cause of the problem but still the same. I have now noticed that there is a second microswitch which is also activated by a drop in water pressure on the hot water feed located on a brass component behind the pump on the right hand side of the boiler. This unit must contain another diaphragm and some kind of bleed down jet to create a time delay before the boiler lights.
Can anyone tell me what this unit is called (in boiler-speak) so I can at least enquire about getting another or, better still, give me an indication as to how I can get into it without having to strip down the whole thing. Also, is it likely to be some crud in there causing the problem or, as I've heard mentioned here, is it more likely to be a split diaphragm?
Any help would be greatly appreciated,
Cheers, Martin.