Baxi 105e fluctuating DHW temperatures

[Johninsale]

Hi, I have a problem with my baxi 105e producing DHW. When I first turn it on the water runs hot then after a short period of time it goes cold. If I leave it running it runs hot again. I have had an engineer look at it. He diagnosed a faulty diverter valve which he changed. When that didn't work he said that it was down to sludge in the system and as that wasn't covered by my boiler insurance there was nothing he could do. Could this be the cause? The central heating system works fine with no cold spots in the radiators. I have since added some Sentinel X400 into the system and left it running off and on for a few days with no improvement. Am I right in thinking that there are possibly two heat exchangers in this boiler? One for the central heating and one for the DHW. If so, I am thinking that the x400 in the central heating system will not solve the problem. Can anyone explain to me how to go about flushing the boiler? I would be grateful for any advice.
Thanks

 

[gazthepottertonengineer]

You would not be able to flush the boiler through! Your symptoms to me say that your plate heat exchanger is blocked up! When you run the hot water do the temperature lights go right upto 80 ?

 

[Johninsale]

Thanks for the prompt response,
When I run the hot water the temperature lights go steadily up until they reach 80 at which point the boiler switches off and the 80 light flashes for a while. the boiler then switches back on and the other lights steadily light up until it reaches 80 again at which point the boiler shuts down again.
If it is the plate heat exchanger that is blocked, can I flush it in situ or do I have to take it out?
Thanks again for your help.

 

[dcawkwell]

The plate heat exchange is blocked.
Remove it flush and shake through with brick acid.
Job sorted.

 

[Johninsale]

Thanks for the reply, I won't be able to do that for a week or so but I will give it a try and let you know how I go on.
Thanks again.

 

[Johninsale]

I just wanted to let the two guys who suggested that my problem was a blocked plate exchanger that they were right. I did as dcawkwell suggested and it worked a treat. Thanks again!!