Baxi Combi Instant 105e DHW problem

[baxpoti]

From your original post

The boiler operates as it should apart from the preheat function.

Is this the case or not?
If so, have you changed the PCB at any time.

 

[Belfast]

Fro reading the forums it seems that Tony has had a lot to do with these awful boilers. My problem is very common. These boilers work a treat on Central heating but try getting any consistent DHW from it!!
The boiler operates as it should apart from the preheat function.
Turn hot tap on - get warmish water out (Pre heat turned 3/4 on).
Turn hot tap off - boiler shuts off straightaway (no flashing green tap neon). I thought it should always go into preheat mode once a demand for hot water has been called?
I have changed both CH and DHW diaphrams, microswitch loom, and both temperature sensors. system pressure is fairly steady at about 1.5 bar. All the pins seem to be operating ok on the diverter and I am getting 230V to the diverter motor.
One other thing I have read that with zero system pressure, the expansion vessel should be charged to 1 bar? When I tried pumping it up after I changed CH diaphram I could not get any air pressure into it untill after I had repressurised the primary loop.
I am now left with thinking I may need a new expansion vessel or even the heat exchanger could be silted up? Finally could someone advise me that I am ok (legally) to work on the water side? I have not touched anything to do with the gas side. Many thanks - Dave.

Could you please let me know if you managed to resolve your DHW problem my boiler is the same I can't even get enough hot water to run the shower. I too got a bloke out he charged me £50 told me the system needed a new heat exchanger he could not fix the problem himself for at least 2 weeks as the boiler would have to come off the all. I got the exchanger and put it in myself but the problem remains the same. How did you get your boiler fixed?