Water inside pressure gauge and slow drip from underneath

Postby BenB » Sun Jan 15, 2017 5:24 pm

The other day, I noticed that water was dripping from the pressure gauge between our sealed heating system and the expansion vessel. It was dripping frequently (every few seconds) and there was quite a lot of water on the floor. After quickly mopping up I started looking into the underlying issue.

I noticed that the reading on the pressure gauge was at (or possibly exceeding) the 4 bar measure, so I quickly bled the nearest radiator to reduce the overall pressure down to 1.5 bar (heating was on, so water was hot).

It seems to me as though the dripping has stopped, or at least slowed, but it's hard to be certain. To be safe I've rigged up a cut up plastic bottle underneath the gauge to catch any drips, and now I'm trying to understand what happened and what (if anything) I need to do next.

Here's a picture of the set-up (which probably hasn't been touched for circa 30 years):

2017-01-14 13.02.54 (Large).jpg

As I understand it, the expansion vessel is supposed to accommodate the increase in overall system pressure when the water heats up, and as a result, the pressure should change very little between cold and hot (1/4 to 1/2 bar difference). Is this a valid assumption? It looks to me as though ours varies by maybe as much as 1 bar or more.

There's now water inside the pressure gauge, which wasn't there before. Is this going to clear by itself, or is it indicative of a problem?

My current working theory is that the expansion vessel may be failing and that could be part of the reason for the sudden high pressure.

As for the pressure gauge, I assume that shouldn't be dripping and probably just needs to be replaced? I can't be sure, but it looks like this (except mounted on the rear instead of underneath, and 4 bar upper limit):


The red line is set to ~1.5 bar. I don't know if that has any relevance.

Thanks in advance for any guidance you can provide!
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