Evo He Ideal Boiler Hot And Cold DHW

[suityou91]

Here is what I have tried :

Clean secondary heat exchanger (twice)
Replace overheat thermistor.
Replace PCB.
Bleed pump.

Still the DHW oscillating between hot and cold. No errors on the panel.

What else could I have missed?

A new boiler will be an option in the new year but I just need to try and nurse this one through another winter.

 

[terryplumb]

How did you clean the plate HEX ,and establish that you were successful ?

 

[suityou91]

I cleaned it with spirit of salts. I gauged I was successful when it got all the crud out, and when I refitted it the boiler worked flawlessly for a glorious 24 hours. So I removed the HEX and checked and cleaned it again. Worked fine for a week then same problem. The second time of taking it off there was nothing to clean hence why I tried replacing the overheat thermistor.

 

[terryplumb]

If cleaning the plate hex cured the problem ,and it blocked up again a short while later ,you probably haven't been totally successful. Rather than waste money changing parts without knowing they are faulty is false economy. If you were to change anything it would be the plate hex.

 

[suityou91]

If removing the HEX plate reveals that it is not blocked, and yet the problem persists, wouldn't it indicate the problem is elsewhere? If I took the HEX plate off and it was full of crap again I wouldn't have started the thread.

 

[terryplumb]

Why do you think it worked fine for a week after cleaning the plate hex twice ,if the other components you mentioned were faulty ?
You can't see the internal water ways ,and it doesnt need to be totally blocked ,if the flow on the primary side is restricted enough then the symptoms you describe is the result.

 

[suityou91]

Understand and thank you. Can I take from this that it cannot be for any other reason these symptoms are occurring, and focus my attention solely on the HEX?