Heatline Vizo 24 - Sludged Heat Exchanger or?

22 Jan 2013
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United Kingdom
Hi All,

Posted on here once before and got a great answer first time round, so relying on you guys once again!

DHW is going hot and cold. When there is hot water demand, boiler fires up and gives boiling hot water, then after 20 secs the boiler flame cuts out with a click and then reignites about 15 seconds later. This process repeats itself resulting in the hot and cold water. Plate heat exchanger was sludged (removed through back of boiler by removing dhw outlet feed) and has been flushed clean but think I will clean with spirit of salt next.

Question is: is this a sludged heat exchanger issue causing the flame to go out each time as above? Or something else like a sensor? All help appreciated.

Thanks in advance as always.

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That is a description typical of the symptoms of a blocked plate hE.

Citric acid is in many ways better than HCl.

Thanks Tony. Bought a new HE, arrived (Alfa laval cb16 from euro boiler parts) apparently a better replacement than the original. Problem; when I attach it, get a high pressure spray ie: poor seal. All seals find when I put original HE back on. What's going wrong? New o rings? Seem to be working fine on original though. Ensured it was tightened too. Any ideas? Much appreciated.

Welcome to the problems boiler engineers encounter!

I have no idea why yours is leaking but you are dealing with seals out of sight in a restricted access area!

In front of the boiler I could tell you. On the internet I cannot apart from saying its going to be the DHW connection.

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Thanks Tony. Makes sense just to clean old one with citric acid and not worry about the seal issue. Final question (promise!), as this is in a tenant's house - is there a quick or efficient way of cleaning? Ie: I suppose I have to remove HE and leave in citric over night? Can I put citric in heating loop so there isn't 12 hours of heating and dhw 'downtime'?

Just looking for most efficient way to get them up and running ASAP.

Thanks again Tony.

I clean them manually in about 30 minutes!

I do warm up the DHW side with boiling water to speed up the acid action.

Agitating continuously is the key to rapid cleansing.


PS Its not totally unknown to find a new plate is faulty and leaking! It could also be distorted and not applying the correct pressure to the seals. Lining a steel rule against it might help to see that.
I have the exact pproblem described in this article regarding leaking seals on the small hot water plate heat exchanger. However the small heat exchanger appears to be clean. Is it the main heat exchanger in need of cleaning? I also have the intermittent hot/cold cycle with the shower. Any suggestions?

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