Pressure Gauge readings different on sealed system?

[Fitz]

At a relatives house at the weekend and they were complaining of non working rads on their sealed system.

It turned out that they had been overbled and the system not repressurised.

So I set about finding the filling loop (do any plumbers ACTUALLY remove these after installation?) which turned out to be next to the DHW storage tank on the second floor.

On filling the system the gauges on the boiler and next to the filling loop differed by .2 - .3 BAR which seems like quite a bit to me. Would that be considered a normal discrepency? Which is most likely to be accurate the one built into the boiler or the stand-alone unit plumbed in upstairs? There was no tolerence info in the boiler manual.

I guess it doesn't matter too much at the moment because even worst case with the observed error the true pressure wont be anywhere near the 3 BAR it needs to spew it's guts.

[adder1969]

With the higher pressure downstairs or up?

[Roger Mills (aka Set Square)]

If the higher pressure was downstairs, that is to be expected - due to the static head of water. A pressure of 1 bar is equivalent to a static head of about 10 metres - so if one gauge was measuring the pressure at a point 2 or

3 metres higher than the other one, that would be about right.

[John Rumm]

I have seen one where they did!

They are both probably right!

1 bar is roughly equal to the pressure exerted by a water column 10m high. So if your downstairs pressure guage was 2m below the upstairs one you would expect it to read 0.2 bar more. The dowstairs guage will read the sum of the static pressure intruduced into the system, and the pressure exerted due to gravity on the head of water above the guage. The upstairs one will read the same static pressure but obviosly has less head of water above it so the total is less.

For most two story properties a setting of 1 bar when cold on the ground floor will translate to adequate pressure on the top floor.

[Merryterry]

Itis a requirement, under the Water Regulations, that filling loops have to have the hoses removed and either end capped off. There must also be a double checkvalve on the 'live side'.

[Fitz]

I am kicking myself even now for not spotting such an obvious reason.