Expansion Vessel Pressure

28 Nov 2013
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United Kingdom
Can anyone tell me what the pressure is supposed to be in the expansion vessel on my boiler please
Its a Worcester Bosch Greenstar,but not sure if its a 24i or 28i junior is there a difference in pressure
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With the boiler drained you should have a pressure of about 1 bar will be fine. With any water in the system it won't be possible to get an accurate pressure reading.
Same for both.

According to the MI it should be 3/4 bar, so between 3/4 and 1 bar would suffice. Tested at the shraeder valve on the EV with zero pressure in the CH system and a drain point/valve open.

Oops, DC beat me to it :p
The MI will state 0.75 bar, which is as above, if my maths conversion between imperial and metric are still up to scratch?
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Thanks .
the problem with my boiler is the pressure is down to 0 when the boiler is off but when turning the heating on it goes up to the correct pressure and down to 0 again when turned back off
Ive been told that it could be a miner leak but i cant find one so anywhere
Are you talking about system pressure or the pressure in the expansion vessel?

Sounds to me you are talking about system pressure, if you are losing pressure on the CH side there is a good chance you have a leak.
I would check all compression joints, the radiator valves are a good starting point, you may see a little residue staining.
Sorry people but what i know about boilers you could write on the back of a stamp.I would imagine that it is the system pressure looking at the gauge on the front of the boiler.We get hot water and all the rads are hot when the boiler is turned on.But when we turn the boiler off at night the gauge goes down to zero
Have you tried filling to 1 bar, bleed of rads, repeat until you maintain at 1 bar, with rads full. This is done cold. Then see how your system reacts, the pressure will rise when the heating is on, but once the system cools down again then it should settle back to 1 bar.
If you do then start to loose pressure a little more investigation will be required.

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