Plumbing/central Heating Gauge Query

[Old_Geezer]

Unsure which forum this goes in so trying DIY.

Passing my airing cupboard I heard a gurgling, which usually means I should look at the pressure gauge above the pressured container, which is above the hot water tank, to ensure it's high enough.

Removed the stuff in front of the gauge to check it, and was immediately confused. It has two hands ! (Unsure why I didn't remember that but it's presumably not confused before.)

The black hand is at the top of the part of the dial coloured green, the red is at the bottom of the green area. I've no idea how to interpret that. Is the black hand telling me it is at max acceptable pressure, or is the red hand telling me it's at min acceptable pressure ? What is each for ? And why are they where they are ?

I'm taking it as indicating all is well for now, but I'd like to know what it all means.

Cheers.

[Garaman]

Are they not temperature and pressure?

[Old_Geezer]

Interesting thought, but the gauge only says "bar". I note the black hand has dropped now, to mid green area, so I guess that's the one to check; but the red one has me foxed. It's not even as if I can set it anywhere.

[Garaman]

It does seem then as if the red one is just set to Max, either at the factory, or else so that you can do it yourself with a screwdriver or similar tool.

[EDDIE51]

'bar' is a measure of pressure . 1 bar = 14lb/sq inch
(if I have remembered my 'O'level Physics!)

[Buenchico]

Quote:
"Sometimes the gauge dial has both a red and a black needle.

The red one is just an indicator of where the level should be, the thin black needle is the actual pressure,
so the correct pressure can be set by matching the black to the red needle"

Source:
http://www.ggasheat.co.uk/common-boiler-problems.html

[Garaman]

I should imagine that they use a movable red hand as a marker as opposed to marking the dial itself so that the gauges can be used in boilers with different maximums.

[Old_Geezer]

Well this is going to sound rather silly, but no less confusing.

I've just gone and had a really good look and feel of the gauge, looking for any screwdriver slot, or knob for adjusting: and I was about to give up having found nothing when I discovered that the plastic "glass" at the front will pull off. (Without anything escaping :-) )

The red hand isn't a hand at all but is painted on the glass ! Along with a green triangle that matches the one on the back behind the real black hand. Ok so it can be ignored. But I don't know why it, a red hand, is painted there at the low end of the green bit; nor why I didn't get concerned in past years about it.

Anyway the gurgling sound can be ignored.

[EDDIE51]

Can you turn the 'glass' round so the painted on redline points to where you want it to , so as to indicate the maximum pressure you want?

[Old_Geezer]

I could, but then the green "triangle" on the glass wouldn't line up with the green "triangle" on the back. I'd have thought the red "hand" was superfluous, the green range is obvious anyway.

[DocHH]

I suspect you are referring to a condenscing boiler located in your airing cupboard, if that is correct I think the red arrow is indicating the minimum required "pressure" ( in Bars) and the black arrow indicating the "actual" pressure. The green area probably is the acceptable range of pressures. In which case if the black arrow is above the red arrow it is telling you to ignore the gurgling.

[Old_Geezer]

The boiler is downstairs; this gauge is above the red "expansion vessel" in the airing cupboard. But aside from that I think you are correct. I think I was puzzled today because of the coincidence of both "hands" being either end of the green section. Or indeed why there is a red hand at the bottom when it doesn't really add to the green section indication. I've stopped being concerned for now anyway. Thanks.