Greenstar 30i Boiling loosing pressure (wierd)

You don't need to identify the cause of the problem ,that's what the engineer does. You just tell them the symptoms, as you have described here.

terryplumb said:

You don't need to identify the cause of the problem ,that's what the engineer does. You just tell them the symptoms, as you have described here.

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I understand what you are saying and thats what i did before, but without the boiler having an issue when the he arrives its obviously difficult to find an issue. I even have many video recordings of the boiler working perfectly as I was trying to get a video of the fault but it happens so rarely that I have never yet been able to catch it on video!
Just trying to establish if there is any more long term Problem Determination to try and trap this fault (calling engineers today, loooks like I have a 3 week wait anyway)

flibberflops said:

Worcester-Bosch Greenstar 30i

The Pressure gauge is dropping about 0.1 bar everytime the radiator burner/pump kicks in. If I put the heating on it goes down from 1 bar to zero in about 2-3 hours. (constantly dropping 0.1 bar everytime the burner kicks in until reaches zero).

If I pressurise the system to 2 bar and leave overnight without use, it is still two bar in the morning (so I am pretty confident its not the rads/pipes)

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This is indicative of a failed expansion vessel, as you have subsequently discovered. You may also need to attend to a dripping PRV.

flibberflops said:

I have also noticed that when the hot water is turned on, the pressure will drop 0.25 bar while the hot water is running before returning back to previous presure reading when the hot water is turned off.

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This is normal, and a function of the pressure drops around the boiler when the pump runs.

flibberflops said:

I have also noticed that the hot water still works even though the presure gauge is reading zero (I thought there was supposed to be a complete system cutoff when the presure drops too low?)

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So did I....get the gas fitter to check that there IS a pressure switch, and that it's working.

flibberflops said:

Cannot find a leak anywhere... including around the boiler area or external pressure relief pipe. I cannot easily monitor the condensation pipe due to the way that it has been plumbed in.

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Look again, if the expansion vessel has failed and the pressure has been reaching 3.5 bar then you've missed something.

PS that's a very weird spelling of weird. You don't see that very 'oftern'.

Just a quick update... The Boiler is now fixed.

It was the expansion vessel (and other parts needed replacing). The problem was caused by a massive amount of sludge... in fact when the old expansion vessel was taken out despite it being empty of water it was like lifting a Gold Bar!

I am slightly mistified how this has happened. The boiler is 10 years old but i have only lived here for 3. During that time I have replaced 7 of the 10 radiators and everytime I have replaced one the water comming out of the radiator looked pretty good + I have always added a bottle of inhibbiter to every new radiator install!

Still the engineer has advised I get a flush + add a filter to the CH return.