Vokera Excel 80SP - Noise and Pressure Problem

23 Jul 2006
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United Kingdom
We have a Vokera Excel 80SP and over the last 3-4 months, the boiler has started making noises mainly when the hot water tap is run. It sounds like a loud rattling/banging. It does it for about 5-10 seconds when the hot water is run for the first time for a while. After this, its fine for a while, even if the hot water tap is switched off and on in between.

Interestingly, the hot water pressure also drops to just above 0 bar whilst this noise occurs and then slowly rises again when the system isn't used for a while, back up to 1.5 bar over the course on about an hour.

The auto air vent also seems to be leaking - could this be contributing?

Any ideas on what this could be - the drop in pressure is worrying, it almost makes me think there is something wrong with the flow diverter but being new to combi boilers, I would like some advice before I call somebody out.

The noise and vibration seemed to have caused the supply value to the main heat exchange to become loose - another leak, so I want to resolve this before it happens again.

Thanks in advance and great forum! :)
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In a nutshell, boiler is overdue a service.

For starters, system pressure is FAR TOO LOW. Pressure guage is nothing to do with hot water at the tap. If you do not raise the pressure as of yesterday, you will soon be looking for a new boiler.

Good possibility that the auto air vent has failed due to lack of water. They also fail if the system water is dirty.
Could well be the auto air vent leaking pressure away. Suggest presurising to 1.5 and then check the auto air vent - if leaking replace. As mentioned crap in the system is number one cause of air vents leaking .
Fit a Magnaclean and you will be astonished at the amount of metallised crap clinging to the magnet. Could also be your Pressure unit.
Thanks for the advice. Just to confirm - the boiler pressure is at 1.5-2 bar when cold but drops when either the hot water or central heating is run to zero. I would expect this to work the other way round - any ideas what is causing this?
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Lack of air charge in the expansion vessel.

Just possibly could be a leak across the secondary heat exchanger.

As usual a competent boiler engineer should be able to sort it out quickly.


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