Boiler venting.....

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In a nutshell, we bought a house recently, big 3 storey Edwardian job. The previous owners had fitted an Atag boiler of good size, and technically it's still within guarentee but only via the manufacturer as sadly the fitter died just before they moved, so the installation is not covered any more

To cut to the chase, it has a 25 litre auxilary expansion bottle fitted, which states that it was pre-charged to 1.5 bar, but it still is not stable and the boiler vents water via the overpressure valve regularly and requires topping up a couple of times a week.
From written notes it seems that the previous owners just lived with this, probably because they were selling and didn't want the expense of calling in a engineer?

There are 14 rads of various sizes, the boiler seems quite hefty(could find out) and the expansion vessel is 25 litres plus the one in the boiler. I guess my question is..... should I raise the pre-charge to account for the 3 storeys, and the associated increase in head of water? The expansion bottle suggests it can operate up to 4 bar.

I guess a second expansion vessel wouldn't be a bad thing but if I can get away with just pumping up the current one a bit to get us through until spring next year????
 
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I would say that it is more likely the expansion vessels have lost their charge.
Drain down the system. Pump each expansion vessel to about 1.25 bar.

Put some washing up liquid water onto the tyre valve to make sure
the tyre valve isn't leaking. Refill up to 1 bar .

Sorted.
 
I personally would not want to pump the pressure up to much it puts a strain on all the boiler seals (3bar max) and if the expansion vessel isn't big enough capacity when the system starts to heat up, the cold system pressure should be 3/4 - 1bar and when system hot no more than 2 bar. if it goes any higher and the exp vessel is not faulty (pressing valve to release air if water comes out new vessel needed). Get an extra vessel fitted sooner rather than later. every time you re-pressurise you make sludge.
 

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