Worcester Bosch 37 CDi Combi hot water problems

[U689798]

Hoping someone can help?
I have a 2 year old 37CDi boiler and everything was fine for first 20 months or so. Now however I have a big problem with it:
I have a dt20rf programmer installed with wireless thermostat and irrespective of the pre-heat hot water setting on the programmer, whenever I turn any hot water tap on it comes nice and hot for about 15-20 seconds and then goes cold again. I have checked the pressure and refilled it a couple of times back up to just under 1.5 on the gauge but no luck, only hot water for 20 seconds and then cold again. I leave the boiler for several minutes then go back and turn tap on and same thing happens all over again, hot water for 20 seconds and then cold. Heating seems fine when demand is on.
PLEASE HELP !!!!!ANY ADVICE VERY MUCH APPRECIATED .
THANKS IN ADVANCE

Just found out that when the heating is on, the hot water comes through perfectly fine all of the time with no drop in temp/pressure, but switch the heating off and within 20 seconds the hot water has gone cold again. Could it be the DHW sensor?

 

[St0rmer66]

If you turn the preheat off do you get no hot water at all?

If so then along with what you've already said it sounds like the dhw flow turbine. If it's only 20 months old then you should be under warranty so ring Worcester.

 

[U689798]

Thanks for taking the time to reply to my problem.
The Pre-heat being on or off makes absolutely no difference to the problem. The only way I can get hot water for more than 20 seconds is to have the heating on. You say it might be the DHW Turbine? Where is the Turbine? I did not install the boiler but am an Aircraft Engineer so have some Mechanical background and if it is the DHW sensor I know where this is and can easily obtain a replacement and do the job myself. The boiler started to play up when it was 20 months old and when it first started doing this , it would only be intermittent, ie it would work fine for 2 or 3 weeks and then it would play up for a few days before working fine again. It is only now that it is always like this.
The boiler is now just over 2 years old and even though I got Worcester's 5 year guarantee I stupidly did not get the first service done and I assumed they would not honour the warranty after this?
Thank you again for taking the time to reply so quickly.
Regards

 

[U689798]

Thanks for taking the time to reply to my problem.
The Pre-heat being on or off makes absolutely no difference to the problem. The only way I can get hot water for more than 20 seconds is to have the heating on. You say it might be the DHW Turbine? Where is the Turbine? I did not install the boiler but am an Aircraft Engineer so have some Mechanical background and if it is the DHW sensor I know where this is and can easily obtain a replacement and do the job myself. The boiler started to play up when it was 20 months old and when it first started doing this , it would only be intermittent, ie it would work fine for 2 or 3 weeks and then it would play up for a few days before working fine again. It is only now that it is always like this.
The boiler is now just over 2 years old and even though I got Worcester's 5 year guarantee I stupidly did not get the first service done and I assumed they would not honour the warranty after this?
Thank you again for taking the time to reply so quickly.
Regards

 

[jeff the gasman]

Just re read your post!