Central Heating Pressure

[Bilbo Baggins]

I've recently had a mains pressure unvented hot water system fitted and I am absolutely delighted with it (fantastic shower pressure without any noisy pumps).

My question relates to the pressure vessel for the central heating system. The vessel has a pressure gauge and a water feed attached and my plumber recommended that I have it set at 1 bar pressure. When the system is idle the pressure is currently 1 bar and when it's in demand it's nearly 2 bar.

Is this correct or should I have it running at 1 bar ? I don't want to run it at too high a pressure and risk the rather aged pipework springing a leak.

KW

[BigWallop]

Heat causes things to expand and water is no exception. The rise in pressure is natural.

Just make sure that all the radiators are full of water and not air, but if it is a neaw system, then this will already have been done, so leave it alone until it doesn't do its job correctly.

In other words, If it ain't broke, then why try to fix it. :-))

[Andrew Gabriel]

That sounds correct. 1 bar when cold will ensure highest points in the system stay pressurised as long as they aren't more than

30' above the height of the pressure guage. Pressure always goes up when system heats up. For most systems, it mustn't get to 3 bar, or the pressure relief valve will operate (would indicate the expansion vessel is too small, or lost it's pressure).

[Christian McArdle]

That sounds like it is behaving precisely as designed. When filling or checking the system, ensure it is cold. If it rises above 2 bar, then you may have a problem, though. This would probably be an undersized or malfunctioning expansion vessel.

BTW, this is totally unrelated to the fact you have an unvented hot water cylinder. It is the pressurisation of the primary circuit which requires the pressure gauges and filling loops. You can have this system on a gravity fed hot water cylinder too. It sounds like it was converted at the same time as the cylinder was installed, though.

Christian.

[Ed Sirett]

Take a look below. The rise is rather on the large size and if there were a lot of rads and/or the old fashioned 'school' type then another expansion veseerl might be needed - Or maybe the existing unit is faulty or wrongly set up.

[Bilbo Baggins]

Thanks guys,

I realise that the unvented water system is not directly connected but I just wanted to show off ;-)

I had the system installed a few months ago and although the plumber fired up the heating to test it it wasn't run for any length of time and hasn't been used in earnest until now. After the first few days i had to bleed a lot of air out of the system. When I bled the air out I had to let some water into the pressure vessel to compensate. Now it seems to have settled down nicely and I am glad that it is running at the correct pressure (1 bar when cold and 1.5 (ish) when up and running)

Thanks again.

KW

[Andy Hall]

This is fairly normal.

Just one other thing..... Have you put in some inhibitor??

.andy

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