Vaillant Heat Exchanger NOT blocked?

[Christian and Beccy]

So, my Vaillant Turbomax Plus 837e displays the signs of having a blocked DHW Heat Exchanger (hot water temp cycling hot/cold).

I've removed it, expecting to see a gunked up mess, but frankly it wasn't as expected. I've run water through it in all directions, seems to flow and it's currently sitting outside filled with Hydrochloric Acid but I'm no longer inspired that it's the cause.

Beyond this, what could be next? I'll call someone out if this doesn't fix it, but would love an idea of what to expect...

 

[Agile]

There can be several causes of DHW going hot/cold apart from a blocked plate HE.

But the first thing that I would be asking for is an accurate measurement of the flow/return temperature in the boiler during DHW delivery.

Then I would dynamically measure the resistance of the temp sensors by measuring the voltage across them.

I would also ask what fault/status codes it shows.

But some possible causes are gas related and for that we cannot give you advice here.

Tony

 

[Christian and Beccy]

I should have had faith. Cleaned the Heat Exchanger thoroughly, reinstalled in, fired the boiler up and bingo! Seems to be fixed.

Better still, I've turned the DHW down by 8°c so far as the cleaner Heat Exchanger has resulted in much hotter water for the same boiler temperature setting. Might need turning down a little more yet, should make for a decent gas bill saving.

 

[Whitespirit66]

When you take out a blocked plate hex, you won't see a "gunked up mess". Two of the ports on the hex will look darker inside than the other two. These are the primaries where water circulates to/from the main hex. Filling it with tap water then holding the blocked plate hex upside down and tapping one of these primary ports on the palm of your hand will usually get some small rust flakes coming out. That's only the tip of the iceberg, as most debris will be stuck inside between the plates.

Undoubtably the acid you used dissolved a lot of the rust in the hex - hence it's increased performance. However, it's likely that your system water that runs through the boiler and rads is dirty, and will gradually block the hex again. A thorough system flush, correct inhibitor concentration and poss a magnetic filter on boiler's return pipe may be needed.

 

[Christian and Beccy]

Thanks Whitespirit66, I'm very likely to fit a Magnaclean, something I was advised to do a few years ago by a good friend of mine. I stupidly never got round to doing it, but I'll take this as the push.

During the renovation of my bungalow, I've lost count of how many times the heating system has been drained and refilled so the water tends to come out clean these days, but on the other hand, how long it's spent without any kind of filtration or inhibitor so I guess I should have expected this.

The heating system is now complete, well, except one more radiator I want to change, but once I get that done, it'll get left alone.