Faulty Alpha c28 boiler - Low pressure & No hot water

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15 Nov 2010
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Hi, Would appreciate some help Please

Have read many posts with a similar problem but nothing matches exactly.

Boiler is Alpha CB28

The pressure falls overnight leaving me with zero pressure in a morning so i top it up to the middle of the green band and the alternately flashing lights go out and the boiler springs into life.

The central heating works fine and the hot water works ok currently but last week the hot water would not work unless the boiler was firing so i ran baths and showered with the central heating on constant and the thermostat turned up high.

When the boiler cools the pressure drops and needs refilling.

I have checked the flow switch on the diverter valve and that is in good order. (The boiler came on when detached) Strangely since i replaced the flow switch the hot water has worked but the pressure still falls.

Put balloon over PRV and no water is collected although while checking the flow switch i turned the PRV and it worked fine. (water in the balloon)

There is no leak or at least no sign of a leak through the house and i am pretty sure one would have come to light by now if there was as i have been refilling the system for a week now.

When the hot water was intermittent i was thinking it was the diverter valve / diaphragm but now am swinging to the expansion vessel.

Any ideas ??????????????????? Thanks
 
1st check the pre charge in the exp vessel.The schraeder valve is located top rear of boiler.Make sure the system is fully depressurised b4 doilng this(drain via rad or dran cock)Test pressure and if not approx .8bar then pump it up to that pressure.Refill system and test run.
I would change the diaphragm in the div valve(access not great with pump in position)and see how you go.None of this work is gas related so is DIYable.Don't forget pcb's and water do not mix.
 
Hi Guys Please help me ! ! ! ! !
I have same problem , but when my pressure drops to zero i don't know how to get it back up again , so every morning when it happens i have to ring the repairs and have to wait 2-3 days .... *sob*sob*
PLEASE HELP
 

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