Expansion vessel pressure v boiler pressure

[trevorbayliss]

Are the two pressures the same when the boiler is working normally ? I thought the expansion vessel pressure must be at around 1 bar and the boiler pressure might be say at 1.5 bar.

I've just checked my EV and it is 1.4 Bar, the same as the boiler pressure.

I recharged the vessell a few weeks ago and set it at 0.95 bar. This was while the boiler had been drained down, so i did it correctly.

Just wondering if my loosing pressure problems are caused by the EV now? It is coming up to 16y/o in april.

 

[ScottishGasMan]

When you rechecked it was the boiler pressure at zero or did you still have water pressure in the boiler? Can only check EV accurately when system pressure has been dropped out

 

[trevorbayliss]

No the system was pressured normally at 1.4 bar.

So do i need to drain the boiler down to find the correct pressure of the EV ?

 

[Johntheo5]

Are the two pressures the same when the boiler is working normally ? I thought the expansion vessel pressure must be at around 1 bar and the boiler pressure might be say at 1.5 bar.

I've just checked my EV and it is 1.4 Bar, the same as the boiler pressure.

I recharged the vessell a few weeks ago and set it at 0.95 bar. This was while the boiler had been drained down, so i did it correctly.

Just wondering if my loosing pressure problems are caused by the EV now? It is coming up to 16y/o in april.

You should check or precharge the EV air end pressure, with no pressure at the water end to between 0.75br and 1.0 bar, I use 1.0bar, you shoukd then fill it by another 0.5bar, this gives you a water reserve so that you dont have to constantly top up the system, if you precharged the EV to 0.94bar and the filled it (cold) to 1.45bar then you will have a reserve of 2.1L, (assuming a 10L EV) , which you would have to loose/leak before the cold pressure will again fall to o.94, assuming system contents at 85L then the final pressure when system hot will be 2.05bar.

The EV pressure and boiler pressure will be the same except at different elevations, obviously in a system or combi boiler they will be the same.

 

[trevorbayliss]

Ok thanks. I am a little lost regarding filling the pressures.

I have decided to buy a new EV so will get the engineer to fit it next week as I also want a service doing.

I thought you do as you said - make sure all pressure is out of the boiler and then pump up the EV to about 1 bar. I just did it to 0.95 on my pressure gauge.

I then filled the boiler pressure back up to its normal ready state of about 1.5Bar.