Worcester Heatslave 20/25 Expansion vessel initial pressure

[Avocet]

Hi, I'm just about to fit a new expansion vessel It's 12 litres in capacity. Highest point in the central heating system is the towel rail at 3.7m above the expansion vessel. The house has 19 radiators (if you count double radiators as two) or 14 if you don't!

The commissioning instructions that came with the boiler suggest 0.5 Bar. The new expansion vessel is filled to 0.9 Bar at present (not fitted yet). The Calculation of the height x density x gravity gives me 0.36 Bar.

Does anyone have any recommendations as to what I should go for, please?

 

[Terrywookfit]

Leave it at .9bar and see how you go
Your Primary water content of the boiler is about 70ltrs. Plus rads and pipework.

 

[Avocet]

Thanks for that. When you say "see how you get on", what sorts of things should I look for? If (say) the pressure relief valve blows when it's hot, should I reduce the pressure a bit?

 

[Burnerman]

With my Heatslave the vessel air pressure is recommended at 10 psi and the water pressure 1 bar.
When the system heats up, the pressure will rise a couple of psi - nowhere near relief valve lift off at 3 bar. When the system cools the pressure should return to 1 bar.
I've had issues with the water pipe connecting to the EV being blocked with corrosion, likewise with the pressure gauge.
John

 

[Avocet]

With my Heatslave the vessel air pressure is recommended at 10 psi and the water pressure 1 bar.
When the system heats up, the pressure will rise a couple of psi - nowhere near relief valve lift off at 3 bar. When the system cools the pressure should return to 1 bar.
I've had issues with the water pipe connecting to the EV being blocked with corrosion, likewise with the pressure gauge.
John

Ta. I've probably over-filled it a bit. Currently, (boiler running) the gauge is showing 2 Bar. However, I know there's a zero error on the gauge of 0.5 Bar because it reads 0.5 Bar when it's not screwed into anything! It has a movable red needle which has been set to 1.5 Bar ever since we've lived here, so I filled the system to that pressure. However, that's still 1 Bar, even accounting for the zero error, so maybe I should drop it a bit. I'll have a last bleed of the radiators later on and if I get no air out, I'll drop it to just over (an indicated) 1 Bar when cold.