Air trapped in water side of expansion vessel.

[SYS49152]

I had a new 18L EV for my heating system fitted today. It came with a 1.5 bar pre-charge and that's how it was fitted. I forgot to suggest to the plumber that it be reduced to about 1 bar before fitting. The EV is mounted with the water feed at the top and nitrogen at the bottom.
I am seeing the pressure vary between 1 bar (cold) and 2 bar (hot). My EV is the highest point in my heating (only just) and when the system is hot, the pipework leading to the top of EV is cold. To me this would suggest that there is air trapped at this high point from the work earlier today?

Is this likely to be the case and if so how can I bleed it? I will attach some photos to better explain the situation. The blue area is where it is cold. The pipework below the blue area is hot.

 

[cross thread]

You could slacken a connection,I would advise that the iron socket is replaced with a brass one

 

[SYS49152]

Thanks, that's what I was thinking but was just wondering if there was something else that I might be overlooking.

Which iron socket are you referring to?

 

[cross thread]

Looks like one adapting to the gauge,

 

[SYS49152]

Just had to go take another look and I think you're right. I never noticed that before and it's been installed for over 20 years.

 

[Jajodu]

Why is there what appears to be a drayton TRV on the feed to the cylinder?

 

[SYS49152]

It is attached to the thin coiled wire which itself is attached to a sensor on the side of the cylinder. I think it's to do with overheating protection <shrug>.

 

[Jajodu]

I can see the cutout in the cylinder insulation where a normal stat would be? You do have a cylinder stat?

I reckon that is your stat, never seen a rad TRV used like that.

 

[SYS49152]

"which itself is attached to a sensor on the side of the cylinder"

The black thing which is just visible in the insulation cutout.

 

[Johntheo5]

That control is known as a tapstat.

 

[Jajodu]

What's its purpose?

 

[ianmcd]

What's its purpose?

It controls the temperature of the HW in the cylinder, very old time design now, I would recommend a proper upgrade

 

[Jajodu]

I thought it had to as it was controlling the heating coils. Time for the OP to upgrade I reckon.

 

[Johntheo5]

I had very good experiences with these many many years ago where the (ships) DHW and various other requirements were heated with steam coils, we used to set the set point temperature 5C above the required temperature as these had ~ 10C hysteresis so the control valve would be open 50% at the required temperature and 100% open at the SP-10C, it just meant that the final temp would end up a little above the required temp with no demand, the advantage of on/off control with a cylinder stat and motorized valve is that the valve goes full open at say SP-8C and remains fully open until the SP temp is reached leading to faster recovery times.