Vizo 24 Boiler - Losing/Gaining Pressure - Some tests done

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We have a Heatline Vizo 24 condensing combination boiler which is about 3 years old.

For the last few weeks the pressure has been dropping slowly (when not being used) from an initial pressure of 1.5 bars, to around 0.8 bars - resulting in the boiler not coming on. When it is on, the pressure increases to over 3 bars over a 15-30 minute period, and therefore cuts out.

We also tried testing the pressure in the expansion vessel with some difficulties, but this was done about a week ago and the pressure was reset to 1.5 bars (the manufacturers recommended amount).

We have isolated the radiators by turning off the two flow/return valves on the boiler. That has resulted in the pressure still dropping (by around 0.2 bars) over a 12 hour period. (The boiler wasn't on at all during this time).

We have checked the plastic condensing pipe on the boiler for water by placing the end of the pipe into a saucer, and leaving the boiler off for several hours. During this time nothing came from the pipe.

The copper overflow pipe (the one outside) has been checked by attaching a plastic bag to it for a few days. The result has been a very small amount of water coming from it - but it is difficult to tell, as it may just be a little condensation.

Does anyone have any other ideas on what may be causing this, or any other tests we can do to try and narrow down the cause of the issue ?

Thanks in advance for any assistance you are able to provide.

Daniel
 
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you havent checked the expansion vessel properly you need to follow ALL the steps, you MUST have a drain point open when re-pressurising
 
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you havent checked the expansion vessel properly you need to follow ALL the steps, you MUST have a drain point open when re-pressurising

Thanks for your reply.

Do you have details on the steps we need to follow ? - We have just been testing logically.

We did let the pressure on the boiler go down to zero (via a radiator valve).

Thanks
Daniel
 
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but you must leave that radiator valve open to drain the vessel while you re-pressurise it, read the wiki there are instructions there how to do it properly
 
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Thank you very much for your reply.

I've read through the page http://www.diynot.com/wiki/plumbing:faq:faq7 and the big thing we seem to have missed is the fact we need to leave the radiator valve open when doing this.

If after following this to the letter the problem still exists, is the next likely cause a faulty pressure relief valve ?
 
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no a faulty pressure releif valve just drips all the time the only two causes for the symptoms you have are a faulty/depleted expansion vessel or a blockage in the communication hose /pipe somewhere
 
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We have checked the communication hose and it seems to be fine (from what we can tell).

We have also replaced the expansion vessel with an external one, and again after the system is on for less than 10 minutes, the pressure goes from 1.5 bar to 3 bar.

Any other ideas ? :(

Thanks
Daniel
 
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We have also replaced the expansion vessel with an external one, and again after the system is on for less than 10 minutes, the pressure goes from 1.5 bar to 3 bar.

What we have found out is the following.....

What does the flexible hose that goes to the expansion vessel actually go to ? - It would appear that although the hose isn't blocked, water isn't flowing into the expansion vessel.

Any help would really be appreciated.

Thanks
Daniel

Read more: http://www.diynot.com/forums/plumbi...ressure-some-tests-done.383295/#ixzz2lSkNz84T
 
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Thank you once again for your help - It turns out the hose was in fact blocked. We have now unblocked it. (It was blocked at the far end away from the vessel).

For future reference does anyone know the name of this hose and the part number incase it turns out it needs to be replaced ?

Thanks in advance,

Daniel
 
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