Unvented Indirect Tundish Discharge - What Reason?

19 Sep 2011
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United Kingdom
Hello knowledgeable folks.

I have an issue that occurred about a year ago and has come up again.

I have a Santon Premier Indirect Unvented heating cylinder and when the heating system is running there appears to be water discharge from the tundish.

This is not a constant discharge, because I've never "caught it in the act" but I can feel wetness around the tundish and water accumulates in the tray I've put on the floor beneath it (I'm assuming it's gushing out the tundish and spilling over the edges which is why it's not all contained within the discharge pipe & bowl - as opposed to a slow drip). Probably about 100-200ml liquid each day when the heating is on.

I will of course be getting a professional in to look at this but last time someone came in to look at this issue they topped up the expansion vessel pressure and that seemed to work. Fast-forward about a year and the issue is recurring. Is there any way to know if it's the PRV or TPRV that's the source of the discharge?

The PRV is a 6 bar valve and the pressure gauge for the overall system pressure sits at 1 bar-ish resting and 2 bar when the system is running (which I believe is normal for this set up).

Also, just for my own knowledge and I know I'm probably being thick - I struggle with how increasing the expansion vessel pressure would help; surely higher expansion vessel pressure would lead to higher cylinder pressure and therefore discharge?

Appreciate any advice you guys can give, thanks!
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Air is compressible water is not.
On annual service EVs should have their air pressure checked, both CH and UV EVs.
And recharged accordingly.

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