Boiler pressure loss

3 Feb 2019
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United Kingdom
Hi I have a 10yr old Alpha cd28c boiler that has given faultless service until last week.No hot water.Engineer diagnosed faulty diverter valve and motor.This was replaced and all was well for a day!Then the boiler would lose pressure over the 24hr period and would not start up until water was added via the loop.Engineer came again and diagnosed leaking Pressure Relief Valve.This was replaced and now boiler will lose all pressure when off within 3hrs.Also to note it looks as though water is still leaking out of PRV external pipe.Any guidance would be much appreciated as I will have to call engineer again and it,s all getting rather expensive.
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sounds like your engineer used the PRV to drain the boiler and the valve didnt reseat properly,replacing the valve should have sorted it, set the pressure at 1.5 Bar cold then put the heating on and check the pressure 20 mins later if it is up near 3 Bar then you have an expansion problem and that is why the PRV is operating, that is why it is there
Thanks Ian yes when boiler is running it is close to 3 bar.Does this mean expansion tank has an internal leak or that it needs repressurising? Regards Keith
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Thanks for all info guys,will get engineer(hopefully)to invedtigate tomorrow and will report back.
Well! Now here,s a thing boiler held pressure overnight,fired up this morning no bother.It has a running pressure of 2.2 bar does this sound about right?Also would I be right in assuming that because of this:A)there is no leak in the CH system B) the Epansion Vessel doesn,t leak.The only other factor since the PRV was fitted on Friday is that it didn,t freeze overnight,although this hasn,t been a problem in previous winters.So upshot is I,m holding off calling engineer unless it loses pressure again and if it doesn,t I,ll call him soon to top up inhibitor.
Engineer came this morning,drained boiler and checked EV pressure it was just under a 1 bar so all ok.Drained towel rail and put in 1 cartidge of inhibitor.Recharged system and fired up boiler,running at about 2 bar.Can,t see any leaks in boiler or from PRV so hopefully it will hold pressure overnight and fire up in the morning.Thanks for everyones input.One thing I did learn was to surf the 'net for replacement parts i.e Diverter valve £120, on 'net new internal spindle c/w all seals etc £20 new DV motor £80,on 'net £20 new PRV £30,on 'net £7:80.So a lesson learned all round.
Spoke too soon just checked and there,s water under boiler!!! It was leaking after engineer finished but he traced it to some "valve" that is only open on commisioning so he closed that and it stopped.Cant see now where its coming from as cover is back in place.Oh well have to call him back again!
if it is the AAV they are very common to leak, not just on your boiler but on ,most they tend to pass
There was a leak from this and the engineer turned it off,all was ok for a few hours,now its dripping with heating on.Is it a fix for a competent DIYer? as they,re pennies to buy
Update on this epic saga.AAV didn,t leak a molecule of water overnight but didn,t fire up this morning,recharged system and it fired up.Water leaked straight away,approx quarter cupful,and then stopped.I took front off and checked on top of AAV,water all over it.Dried it off and it,s now been running for 2 hours without leaking.Engineer coming this morning to fit new AAV.What next?

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